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linuxdebug/tools/lib/bpf/usdt.c

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// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libelf.h>
#include <gelf.h>
#include <unistd.h>
#include <linux/ptrace.h>
#include <linux/kernel.h>
/* s8 will be marked as poison while it's a reg of riscv */
#if defined(__riscv)
#define rv_s8 s8
#endif
#include "bpf.h"
#include "libbpf.h"
#include "libbpf_common.h"
#include "libbpf_internal.h"
#include "hashmap.h"
/* libbpf's USDT support consists of BPF-side state/code and user-space
* state/code working together in concert. BPF-side parts are defined in
* usdt.bpf.h header library. User-space state is encapsulated by struct
* usdt_manager and all the supporting code centered around usdt_manager.
*
* usdt.bpf.h defines two BPF maps that usdt_manager expects: USDT spec map
* and IP-to-spec-ID map, which is auxiliary map necessary for kernels that
* don't support BPF cookie (see below). These two maps are implicitly
* embedded into user's end BPF object file when user's code included
* usdt.bpf.h. This means that libbpf doesn't do anything special to create
* these USDT support maps. They are created by normal libbpf logic of
* instantiating BPF maps when opening and loading BPF object.
*
* As such, libbpf is basically unaware of the need to do anything
* USDT-related until the very first call to bpf_program__attach_usdt(), which
* can be called by user explicitly or happen automatically during skeleton
* attach (or, equivalently, through generic bpf_program__attach() call). At
* this point, libbpf will instantiate and initialize struct usdt_manager and
* store it in bpf_object. USDT manager is per-BPF object construct, as each
* independent BPF object might or might not have USDT programs, and thus all
* the expected USDT-related state. There is no coordination between two
* bpf_object in parts of USDT attachment, they are oblivious of each other's
* existence and libbpf is just oblivious, dealing with bpf_object-specific
* USDT state.
*
* Quick crash course on USDTs.
*
* From user-space application's point of view, USDT is essentially just
* a slightly special function call that normally has zero overhead, unless it
* is being traced by some external entity (e.g, BPF-based tool). Here's how
* a typical application can trigger USDT probe:
*
* #include <sys/sdt.h> // provided by systemtap-sdt-devel package
* // folly also provide similar functionality in folly/tracing/StaticTracepoint.h
*
* STAP_PROBE3(my_usdt_provider, my_usdt_probe_name, 123, x, &y);
*
* USDT is identified by it's <provider-name>:<probe-name> pair of names. Each
* individual USDT has a fixed number of arguments (3 in the above example)
* and specifies values of each argument as if it was a function call.
*
* USDT call is actually not a function call, but is instead replaced by
* a single NOP instruction (thus zero overhead, effectively). But in addition
* to that, those USDT macros generate special SHT_NOTE ELF records in
* .note.stapsdt ELF section. Here's an example USDT definition as emitted by
* `readelf -n <binary>`:
*
* stapsdt 0x00000089 NT_STAPSDT (SystemTap probe descriptors)
* Provider: test
* Name: usdt12
* Location: 0x0000000000549df3, Base: 0x00000000008effa4, Semaphore: 0x0000000000a4606e
* Arguments: -4@-1204(%rbp) -4@%edi -8@-1216(%rbp) -8@%r8 -4@$5 -8@%r9 8@%rdx 8@%r10 -4@$-9 -2@%cx -2@%ax -1@%sil
*
* In this case we have USDT test:usdt12 with 12 arguments.
*
* Location and base are offsets used to calculate absolute IP address of that
* NOP instruction that kernel can replace with an interrupt instruction to
* trigger instrumentation code (BPF program for all that we care about).
*
* Semaphore above is and optional feature. It records an address of a 2-byte
* refcount variable (normally in '.probes' ELF section) used for signaling if
* there is anything that is attached to USDT. This is useful for user
* applications if, for example, they need to prepare some arguments that are
* passed only to USDTs and preparation is expensive. By checking if USDT is
* "activated", an application can avoid paying those costs unnecessarily.
* Recent enough kernel has built-in support for automatically managing this
* refcount, which libbpf expects and relies on. If USDT is defined without
* associated semaphore, this value will be zero. See selftests for semaphore
* examples.
*
* Arguments is the most interesting part. This USDT specification string is
* providing information about all the USDT arguments and their locations. The
* part before @ sign defined byte size of the argument (1, 2, 4, or 8) and
* whether the argument is signed or unsigned (negative size means signed).
* The part after @ sign is assembly-like definition of argument location
* (see [0] for more details). Technically, assembler can provide some pretty
* advanced definitions, but libbpf is currently supporting three most common
* cases:
* 1) immediate constant, see 5th and 9th args above (-4@$5 and -4@-9);
* 2) register value, e.g., 8@%rdx, which means "unsigned 8-byte integer
* whose value is in register %rdx";
* 3) memory dereference addressed by register, e.g., -4@-1204(%rbp), which
* specifies signed 32-bit integer stored at offset -1204 bytes from
* memory address stored in %rbp.
*
* [0] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
*
* During attachment, libbpf parses all the relevant USDT specifications and
* prepares `struct usdt_spec` (USDT spec), which is then provided to BPF-side
* code through spec map. This allows BPF applications to quickly fetch the
* actual value at runtime using a simple BPF-side code.
*
* With basics out of the way, let's go over less immediately obvious aspects
* of supporting USDTs.
*
* First, there is no special USDT BPF program type. It is actually just
* a uprobe BPF program (which for kernel, at least currently, is just a kprobe
* program, so BPF_PROG_TYPE_KPROBE program type). With the only difference
* that uprobe is usually attached at the function entry, while USDT will
* normally will be somewhere inside the function. But it should always be
* pointing to NOP instruction, which makes such uprobes the fastest uprobe
* kind.
*
* Second, it's important to realize that such STAP_PROBEn(provider, name, ...)
* macro invocations can end up being inlined many-many times, depending on
* specifics of each individual user application. So single conceptual USDT
* (identified by provider:name pair of identifiers) is, generally speaking,
* multiple uprobe locations (USDT call sites) in different places in user
* application. Further, again due to inlining, each USDT call site might end
* up having the same argument #N be located in a different place. In one call
* site it could be a constant, in another will end up in a register, and in
* yet another could be some other register or even somewhere on the stack.
*
* As such, "attaching to USDT" means (in general case) attaching the same
* uprobe BPF program to multiple target locations in user application, each
* potentially having a completely different USDT spec associated with it.
* To wire all this up together libbpf allocates a unique integer spec ID for
* each unique USDT spec. Spec IDs are allocated as sequential small integers
* so that they can be used as keys in array BPF map (for performance reasons).
* Spec ID allocation and accounting is big part of what usdt_manager is
* about. This state has to be maintained per-BPF object and coordinate
* between different USDT attachments within the same BPF object.
*
* Spec ID is the key in spec BPF map, value is the actual USDT spec layed out
* as struct usdt_spec. Each invocation of BPF program at runtime needs to
* know its associated spec ID. It gets it either through BPF cookie, which
* libbpf sets to spec ID during attach time, or, if kernel is too old to
* support BPF cookie, through IP-to-spec-ID map that libbpf maintains in such
* case. The latter means that some modes of operation can't be supported
* without BPF cookie. Such mode is attaching to shared library "generically",
* without specifying target process. In such case, it's impossible to
* calculate absolute IP addresses for IP-to-spec-ID map, and thus such mode
* is not supported without BPF cookie support.
*
* Note that libbpf is using BPF cookie functionality for its own internal
* needs, so user itself can't rely on BPF cookie feature. To that end, libbpf
* provides conceptually equivalent USDT cookie support. It's still u64
* user-provided value that can be associated with USDT attachment. Note that
* this will be the same value for all USDT call sites within the same single
* *logical* USDT attachment. This makes sense because to user attaching to
* USDT is a single BPF program triggered for singular USDT probe. The fact
* that this is done at multiple actual locations is a mostly hidden
* implementation details. This USDT cookie value can be fetched with
* bpf_usdt_cookie(ctx) API provided by usdt.bpf.h
*
* Lastly, while single USDT can have tons of USDT call sites, it doesn't
* necessarily have that many different USDT specs. It very well might be
* that 1000 USDT call sites only need 5 different USDT specs, because all the
* arguments are typically contained in a small set of registers or stack
* locations. As such, it's wasteful to allocate as many USDT spec IDs as
* there are USDT call sites. So libbpf tries to be frugal and performs
* on-the-fly deduplication during a single USDT attachment to only allocate
* the minimal required amount of unique USDT specs (and thus spec IDs). This
* is trivially achieved by using USDT spec string (Arguments string from USDT
* note) as a lookup key in a hashmap. USDT spec string uniquely defines
* everything about how to fetch USDT arguments, so two USDT call sites
* sharing USDT spec string can safely share the same USDT spec and spec ID.
* Note, this spec string deduplication is happening only during the same USDT
* attachment, so each USDT spec shares the same USDT cookie value. This is
* not generally true for other USDT attachments within the same BPF object,
* as even if USDT spec string is the same, USDT cookie value can be
* different. It was deemed excessive to try to deduplicate across independent
* USDT attachments by taking into account USDT spec string *and* USDT cookie
* value, which would complicated spec ID accounting significantly for little
* gain.
*/
#define USDT_BASE_SEC ".stapsdt.base"
#define USDT_SEMA_SEC ".probes"
#define USDT_NOTE_SEC ".note.stapsdt"
#define USDT_NOTE_TYPE 3
#define USDT_NOTE_NAME "stapsdt"
/* should match exactly enum __bpf_usdt_arg_type from usdt.bpf.h */
enum usdt_arg_type {
USDT_ARG_CONST,
USDT_ARG_REG,
USDT_ARG_REG_DEREF,
};
/* should match exactly struct __bpf_usdt_arg_spec from usdt.bpf.h */
struct usdt_arg_spec {
__u64 val_off;
enum usdt_arg_type arg_type;
short reg_off;
bool arg_signed;
char arg_bitshift;
};
/* should match BPF_USDT_MAX_ARG_CNT in usdt.bpf.h */
#define USDT_MAX_ARG_CNT 12
/* should match struct __bpf_usdt_spec from usdt.bpf.h */
struct usdt_spec {
struct usdt_arg_spec args[USDT_MAX_ARG_CNT];
__u64 usdt_cookie;
short arg_cnt;
};
struct usdt_note {
const char *provider;
const char *name;
/* USDT args specification string, e.g.:
* "-4@%esi -4@-24(%rbp) -4@%ecx 2@%ax 8@%rdx"
*/
const char *args;
long loc_addr;
long base_addr;
long sema_addr;
};
struct usdt_target {
long abs_ip;
long rel_ip;
long sema_off;
struct usdt_spec spec;
const char *spec_str;
};
struct usdt_manager {
struct bpf_map *specs_map;
struct bpf_map *ip_to_spec_id_map;
int *free_spec_ids;
size_t free_spec_cnt;
size_t next_free_spec_id;
bool has_bpf_cookie;
bool has_sema_refcnt;
};
struct usdt_manager *usdt_manager_new(struct bpf_object *obj)
{
static const char *ref_ctr_sysfs_path = "/sys/bus/event_source/devices/uprobe/format/ref_ctr_offset";
struct usdt_manager *man;
struct bpf_map *specs_map, *ip_to_spec_id_map;
specs_map = bpf_object__find_map_by_name(obj, "__bpf_usdt_specs");
ip_to_spec_id_map = bpf_object__find_map_by_name(obj, "__bpf_usdt_ip_to_spec_id");
if (!specs_map || !ip_to_spec_id_map) {
pr_warn("usdt: failed to find USDT support BPF maps, did you forget to include bpf/usdt.bpf.h?\n");
return ERR_PTR(-ESRCH);
}
man = calloc(1, sizeof(*man));
if (!man)
return ERR_PTR(-ENOMEM);
man->specs_map = specs_map;
man->ip_to_spec_id_map = ip_to_spec_id_map;
/* Detect if BPF cookie is supported for kprobes.
* We don't need IP-to-ID mapping if we can use BPF cookies.
* Added in: 7adfc6c9b315 ("bpf: Add bpf_get_attach_cookie() BPF helper to access bpf_cookie value")
*/
man->has_bpf_cookie = kernel_supports(obj, FEAT_BPF_COOKIE);
/* Detect kernel support for automatic refcounting of USDT semaphore.
* If this is not supported, USDTs with semaphores will not be supported.
* Added in: a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
*/
man->has_sema_refcnt = faccessat(AT_FDCWD, ref_ctr_sysfs_path, F_OK, AT_EACCESS) == 0;
return man;
}
void usdt_manager_free(struct usdt_manager *man)
{
if (IS_ERR_OR_NULL(man))
return;
free(man->free_spec_ids);
free(man);
}
static int sanity_check_usdt_elf(Elf *elf, const char *path)
{
GElf_Ehdr ehdr;
int endianness;
if (elf_kind(elf) != ELF_K_ELF) {
pr_warn("usdt: unrecognized ELF kind %d for '%s'\n", elf_kind(elf), path);
return -EBADF;
}
switch (gelf_getclass(elf)) {
case ELFCLASS64:
if (sizeof(void *) != 8) {
pr_warn("usdt: attaching to 64-bit ELF binary '%s' is not supported\n", path);
return -EBADF;
}
break;
case ELFCLASS32:
if (sizeof(void *) != 4) {
pr_warn("usdt: attaching to 32-bit ELF binary '%s' is not supported\n", path);
return -EBADF;
}
break;
default:
pr_warn("usdt: unsupported ELF class for '%s'\n", path);
return -EBADF;
}
if (!gelf_getehdr(elf, &ehdr))
return -EINVAL;
if (ehdr.e_type != ET_EXEC && ehdr.e_type != ET_DYN) {
pr_warn("usdt: unsupported type of ELF binary '%s' (%d), only ET_EXEC and ET_DYN are supported\n",
path, ehdr.e_type);
return -EBADF;
}
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
endianness = ELFDATA2LSB;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
endianness = ELFDATA2MSB;
#else
# error "Unrecognized __BYTE_ORDER__"
#endif
if (endianness != ehdr.e_ident[EI_DATA]) {
pr_warn("usdt: ELF endianness mismatch for '%s'\n", path);
return -EBADF;
}
return 0;
}
static int find_elf_sec_by_name(Elf *elf, const char *sec_name, GElf_Shdr *shdr, Elf_Scn **scn)
{
Elf_Scn *sec = NULL;
size_t shstrndx;
if (elf_getshdrstrndx(elf, &shstrndx))
return -EINVAL;
/* check if ELF is corrupted and avoid calling elf_strptr if yes */
if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL))
return -EINVAL;
while ((sec = elf_nextscn(elf, sec)) != NULL) {
char *name;
if (!gelf_getshdr(sec, shdr))
return -EINVAL;
name = elf_strptr(elf, shstrndx, shdr->sh_name);
if (name && strcmp(sec_name, name) == 0) {
*scn = sec;
return 0;
}
}
return -ENOENT;
}
struct elf_seg {
long start;
long end;
long offset;
bool is_exec;
};
static int cmp_elf_segs(const void *_a, const void *_b)
{
const struct elf_seg *a = _a;
const struct elf_seg *b = _b;
return a->start < b->start ? -1 : 1;
}
static int parse_elf_segs(Elf *elf, const char *path, struct elf_seg **segs, size_t *seg_cnt)
{
GElf_Phdr phdr;
size_t n;
int i, err;
struct elf_seg *seg;
void *tmp;
*seg_cnt = 0;
if (elf_getphdrnum(elf, &n)) {
err = -errno;
return err;
}
for (i = 0; i < n; i++) {
if (!gelf_getphdr(elf, i, &phdr)) {
err = -errno;
return err;
}
pr_debug("usdt: discovered PHDR #%d in '%s': vaddr 0x%lx memsz 0x%lx offset 0x%lx type 0x%lx flags 0x%lx\n",
i, path, (long)phdr.p_vaddr, (long)phdr.p_memsz, (long)phdr.p_offset,
(long)phdr.p_type, (long)phdr.p_flags);
if (phdr.p_type != PT_LOAD)
continue;
tmp = libbpf_reallocarray(*segs, *seg_cnt + 1, sizeof(**segs));
if (!tmp)
return -ENOMEM;
*segs = tmp;
seg = *segs + *seg_cnt;
(*seg_cnt)++;
seg->start = phdr.p_vaddr;
seg->end = phdr.p_vaddr + phdr.p_memsz;
seg->offset = phdr.p_offset;
seg->is_exec = phdr.p_flags & PF_X;
}
if (*seg_cnt == 0) {
pr_warn("usdt: failed to find PT_LOAD program headers in '%s'\n", path);
return -ESRCH;
}
qsort(*segs, *seg_cnt, sizeof(**segs), cmp_elf_segs);
return 0;
}
static int parse_vma_segs(int pid, const char *lib_path, struct elf_seg **segs, size_t *seg_cnt)
{
char path[PATH_MAX], line[PATH_MAX], mode[16];
size_t seg_start, seg_end, seg_off;
struct elf_seg *seg;
int tmp_pid, i, err;
FILE *f;
*seg_cnt = 0;
/* Handle containerized binaries only accessible from
* /proc/<pid>/root/<path>. They will be reported as just /<path> in
* /proc/<pid>/maps.
*/
if (sscanf(lib_path, "/proc/%d/root%s", &tmp_pid, path) == 2 && pid == tmp_pid)
goto proceed;
if (!realpath(lib_path, path)) {
pr_warn("usdt: failed to get absolute path of '%s' (err %d), using path as is...\n",
lib_path, -errno);
libbpf_strlcpy(path, lib_path, sizeof(path));
}
proceed:
sprintf(line, "/proc/%d/maps", pid);
f = fopen(line, "r");
if (!f) {
err = -errno;
pr_warn("usdt: failed to open '%s' to get base addr of '%s': %d\n",
line, lib_path, err);
return err;
}
/* We need to handle lines with no path at the end:
*
* 7f5c6f5d1000-7f5c6f5d3000 rw-p 001c7000 08:04 21238613 /usr/lib64/libc-2.17.so
* 7f5c6f5d3000-7f5c6f5d8000 rw-p 00000000 00:00 0
* 7f5c6f5d8000-7f5c6f5d9000 r-xp 00000000 103:01 362990598 /data/users/andriin/linux/tools/bpf/usdt/libhello_usdt.so
*/
while (fscanf(f, "%zx-%zx %s %zx %*s %*d%[^\n]\n",
&seg_start, &seg_end, mode, &seg_off, line) == 5) {
void *tmp;
/* to handle no path case (see above) we need to capture line
* without skipping any whitespaces. So we need to strip
* leading whitespaces manually here
*/
i = 0;
while (isblank(line[i]))
i++;
if (strcmp(line + i, path) != 0)
continue;
pr_debug("usdt: discovered segment for lib '%s': addrs %zx-%zx mode %s offset %zx\n",
path, seg_start, seg_end, mode, seg_off);
/* ignore non-executable sections for shared libs */
if (mode[2] != 'x')
continue;
tmp = libbpf_reallocarray(*segs, *seg_cnt + 1, sizeof(**segs));
if (!tmp) {
err = -ENOMEM;
goto err_out;
}
*segs = tmp;
seg = *segs + *seg_cnt;
*seg_cnt += 1;
seg->start = seg_start;
seg->end = seg_end;
seg->offset = seg_off;
seg->is_exec = true;
}
if (*seg_cnt == 0) {
pr_warn("usdt: failed to find '%s' (resolved to '%s') within PID %d memory mappings\n",
lib_path, path, pid);
err = -ESRCH;
goto err_out;
}
qsort(*segs, *seg_cnt, sizeof(**segs), cmp_elf_segs);
err = 0;
err_out:
fclose(f);
return err;
}
static struct elf_seg *find_elf_seg(struct elf_seg *segs, size_t seg_cnt, long virtaddr)
{
struct elf_seg *seg;
int i;
/* for ELF binaries (both executables and shared libraries), we are
* given virtual address (absolute for executables, relative for
* libraries) which should match address range of [seg_start, seg_end)
*/
for (i = 0, seg = segs; i < seg_cnt; i++, seg++) {
if (seg->start <= virtaddr && virtaddr < seg->end)
return seg;
}
return NULL;
}
static struct elf_seg *find_vma_seg(struct elf_seg *segs, size_t seg_cnt, long offset)
{
struct elf_seg *seg;
int i;
/* for VMA segments from /proc/<pid>/maps file, provided "address" is
* actually a file offset, so should be fall within logical
* offset-based range of [offset_start, offset_end)
*/
for (i = 0, seg = segs; i < seg_cnt; i++, seg++) {
if (seg->offset <= offset && offset < seg->offset + (seg->end - seg->start))
return seg;
}
return NULL;
}
static int parse_usdt_note(Elf *elf, const char *path, GElf_Nhdr *nhdr,
const char *data, size_t name_off, size_t desc_off,
struct usdt_note *usdt_note);
static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note, __u64 usdt_cookie);
static int collect_usdt_targets(struct usdt_manager *man, Elf *elf, const char *path, pid_t pid,
const char *usdt_provider, const char *usdt_name, __u64 usdt_cookie,
struct usdt_target **out_targets, size_t *out_target_cnt)
{
size_t off, name_off, desc_off, seg_cnt = 0, vma_seg_cnt = 0, target_cnt = 0;
struct elf_seg *segs = NULL, *vma_segs = NULL;
struct usdt_target *targets = NULL, *target;
long base_addr = 0;
Elf_Scn *notes_scn, *base_scn;
GElf_Shdr base_shdr, notes_shdr;
GElf_Ehdr ehdr;
GElf_Nhdr nhdr;
Elf_Data *data;
int err;
*out_targets = NULL;
*out_target_cnt = 0;
err = find_elf_sec_by_name(elf, USDT_NOTE_SEC, &notes_shdr, &notes_scn);
if (err) {
pr_warn("usdt: no USDT notes section (%s) found in '%s'\n", USDT_NOTE_SEC, path);
return err;
}
if (notes_shdr.sh_type != SHT_NOTE || !gelf_getehdr(elf, &ehdr)) {
pr_warn("usdt: invalid USDT notes section (%s) in '%s'\n", USDT_NOTE_SEC, path);
return -EINVAL;
}
err = parse_elf_segs(elf, path, &segs, &seg_cnt);
if (err) {
pr_warn("usdt: failed to process ELF program segments for '%s': %d\n", path, err);
goto err_out;
}
/* .stapsdt.base ELF section is optional, but is used for prelink
* offset compensation (see a big comment further below)
*/
if (find_elf_sec_by_name(elf, USDT_BASE_SEC, &base_shdr, &base_scn) == 0)
base_addr = base_shdr.sh_addr;
data = elf_getdata(notes_scn, 0);
off = 0;
while ((off = gelf_getnote(data, off, &nhdr, &name_off, &desc_off)) > 0) {
long usdt_abs_ip, usdt_rel_ip, usdt_sema_off = 0;
struct usdt_note note;
struct elf_seg *seg = NULL;
void *tmp;
err = parse_usdt_note(elf, path, &nhdr, data->d_buf, name_off, desc_off, &note);
if (err)
goto err_out;
if (strcmp(note.provider, usdt_provider) != 0 || strcmp(note.name, usdt_name) != 0)
continue;
/* We need to compensate "prelink effect". See [0] for details,
* relevant parts quoted here:
*
* Each SDT probe also expands into a non-allocated ELF note. You can
* find this by looking at SHT_NOTE sections and decoding the format;
* see below for details. Because the note is non-allocated, it means
* there is no runtime cost, and also preserved in both stripped files
* and .debug files.
*
* However, this means that prelink won't adjust the note's contents
* for address offsets. Instead, this is done via the .stapsdt.base
* section. This is a special section that is added to the text. We
* will only ever have one of these sections in a final link and it
* will only ever be one byte long. Nothing about this section itself
* matters, we just use it as a marker to detect prelink address
* adjustments.
*
* Each probe note records the link-time address of the .stapsdt.base
* section alongside the probe PC address. The decoder compares the
* base address stored in the note with the .stapsdt.base section's
* sh_addr. Initially these are the same, but the section header will
* be adjusted by prelink. So the decoder applies the difference to
* the probe PC address to get the correct prelinked PC address; the
* same adjustment is applied to the semaphore address, if any.
*
* [0] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
*/
usdt_abs_ip = note.loc_addr;
if (base_addr)
usdt_abs_ip += base_addr - note.base_addr;
/* When attaching uprobes (which is what USDTs basically are)
* kernel expects file offset to be specified, not a relative
* virtual address, so we need to translate virtual address to
* file offset, for both ET_EXEC and ET_DYN binaries.
*/
seg = find_elf_seg(segs, seg_cnt, usdt_abs_ip);
if (!seg) {
err = -ESRCH;
pr_warn("usdt: failed to find ELF program segment for '%s:%s' in '%s' at IP 0x%lx\n",
usdt_provider, usdt_name, path, usdt_abs_ip);
goto err_out;
}
if (!seg->is_exec) {
err = -ESRCH;
pr_warn("usdt: matched ELF binary '%s' segment [0x%lx, 0x%lx) for '%s:%s' at IP 0x%lx is not executable\n",
path, seg->start, seg->end, usdt_provider, usdt_name,
usdt_abs_ip);
goto err_out;
}
/* translate from virtual address to file offset */
usdt_rel_ip = usdt_abs_ip - seg->start + seg->offset;
if (ehdr.e_type == ET_DYN && !man->has_bpf_cookie) {
/* If we don't have BPF cookie support but need to
* attach to a shared library, we'll need to know and
* record absolute addresses of attach points due to
* the need to lookup USDT spec by absolute IP of
* triggered uprobe. Doing this resolution is only
* possible when we have a specific PID of the process
* that's using specified shared library. BPF cookie
* removes the absolute address limitation as we don't
* need to do this lookup (we just use BPF cookie as
* an index of USDT spec), so for newer kernels with
* BPF cookie support libbpf supports USDT attachment
* to shared libraries with no PID filter.
*/
if (pid < 0) {
pr_warn("usdt: attaching to shared libraries without specific PID is not supported on current kernel\n");
err = -ENOTSUP;
goto err_out;
}
/* vma_segs are lazily initialized only if necessary */
if (vma_seg_cnt == 0) {
err = parse_vma_segs(pid, path, &vma_segs, &vma_seg_cnt);
if (err) {
pr_warn("usdt: failed to get memory segments in PID %d for shared library '%s': %d\n",
pid, path, err);
goto err_out;
}
}
seg = find_vma_seg(vma_segs, vma_seg_cnt, usdt_rel_ip);
if (!seg) {
err = -ESRCH;
pr_warn("usdt: failed to find shared lib memory segment for '%s:%s' in '%s' at relative IP 0x%lx\n",
usdt_provider, usdt_name, path, usdt_rel_ip);
goto err_out;
}
usdt_abs_ip = seg->start - seg->offset + usdt_rel_ip;
}
pr_debug("usdt: probe for '%s:%s' in %s '%s': addr 0x%lx base 0x%lx (resolved abs_ip 0x%lx rel_ip 0x%lx) args '%s' in segment [0x%lx, 0x%lx) at offset 0x%lx\n",
usdt_provider, usdt_name, ehdr.e_type == ET_EXEC ? "exec" : "lib ", path,
note.loc_addr, note.base_addr, usdt_abs_ip, usdt_rel_ip, note.args,
seg ? seg->start : 0, seg ? seg->end : 0, seg ? seg->offset : 0);
/* Adjust semaphore address to be a file offset */
if (note.sema_addr) {
if (!man->has_sema_refcnt) {
pr_warn("usdt: kernel doesn't support USDT semaphore refcounting for '%s:%s' in '%s'\n",
usdt_provider, usdt_name, path);
err = -ENOTSUP;
goto err_out;
}
seg = find_elf_seg(segs, seg_cnt, note.sema_addr);
if (!seg) {
err = -ESRCH;
pr_warn("usdt: failed to find ELF loadable segment with semaphore of '%s:%s' in '%s' at 0x%lx\n",
usdt_provider, usdt_name, path, note.sema_addr);
goto err_out;
}
if (seg->is_exec) {
err = -ESRCH;
pr_warn("usdt: matched ELF binary '%s' segment [0x%lx, 0x%lx] for semaphore of '%s:%s' at 0x%lx is executable\n",
path, seg->start, seg->end, usdt_provider, usdt_name,
note.sema_addr);
goto err_out;
}
usdt_sema_off = note.sema_addr - seg->start + seg->offset;
pr_debug("usdt: sema for '%s:%s' in %s '%s': addr 0x%lx base 0x%lx (resolved 0x%lx) in segment [0x%lx, 0x%lx] at offset 0x%lx\n",
usdt_provider, usdt_name, ehdr.e_type == ET_EXEC ? "exec" : "lib ",
path, note.sema_addr, note.base_addr, usdt_sema_off,
seg->start, seg->end, seg->offset);
}
/* Record adjusted addresses and offsets and parse USDT spec */
tmp = libbpf_reallocarray(targets, target_cnt + 1, sizeof(*targets));
if (!tmp) {
err = -ENOMEM;
goto err_out;
}
targets = tmp;
target = &targets[target_cnt];
memset(target, 0, sizeof(*target));
target->abs_ip = usdt_abs_ip;
target->rel_ip = usdt_rel_ip;
target->sema_off = usdt_sema_off;
/* notes.args references strings from Elf itself, so they can
* be referenced safely until elf_end() call
*/
target->spec_str = note.args;
err = parse_usdt_spec(&target->spec, &note, usdt_cookie);
if (err)
goto err_out;
target_cnt++;
}
*out_targets = targets;
*out_target_cnt = target_cnt;
err = target_cnt;
err_out:
free(segs);
free(vma_segs);
if (err < 0)
free(targets);
return err;
}
struct bpf_link_usdt {
struct bpf_link link;
struct usdt_manager *usdt_man;
size_t spec_cnt;
int *spec_ids;
size_t uprobe_cnt;
struct {
long abs_ip;
struct bpf_link *link;
} *uprobes;
};
static int bpf_link_usdt_detach(struct bpf_link *link)
{
struct bpf_link_usdt *usdt_link = container_of(link, struct bpf_link_usdt, link);
struct usdt_manager *man = usdt_link->usdt_man;
int i;
for (i = 0; i < usdt_link->uprobe_cnt; i++) {
/* detach underlying uprobe link */
bpf_link__destroy(usdt_link->uprobes[i].link);
/* there is no need to update specs map because it will be
* unconditionally overwritten on subsequent USDT attaches,
* but if BPF cookies are not used we need to remove entry
* from ip_to_spec_id map, otherwise we'll run into false
* conflicting IP errors
*/
if (!man->has_bpf_cookie) {
/* not much we can do about errors here */
(void)bpf_map_delete_elem(bpf_map__fd(man->ip_to_spec_id_map),
&usdt_link->uprobes[i].abs_ip);
}
}
/* try to return the list of previously used spec IDs to usdt_manager
* for future reuse for subsequent USDT attaches
*/
if (!man->free_spec_ids) {
/* if there were no free spec IDs yet, just transfer our IDs */
man->free_spec_ids = usdt_link->spec_ids;
man->free_spec_cnt = usdt_link->spec_cnt;
usdt_link->spec_ids = NULL;
} else {
/* otherwise concat IDs */
size_t new_cnt = man->free_spec_cnt + usdt_link->spec_cnt;
int *new_free_ids;
new_free_ids = libbpf_reallocarray(man->free_spec_ids, new_cnt,
sizeof(*new_free_ids));
/* If we couldn't resize free_spec_ids, we'll just leak
* a bunch of free IDs; this is very unlikely to happen and if
* system is so exhausted on memory, it's the least of user's
* concerns, probably.
* So just do our best here to return those IDs to usdt_manager.
* Another edge case when we can legitimately get NULL is when
* new_cnt is zero, which can happen in some edge cases, so we
* need to be careful about that.
*/
if (new_free_ids || new_cnt == 0) {
memcpy(new_free_ids + man->free_spec_cnt, usdt_link->spec_ids,
usdt_link->spec_cnt * sizeof(*usdt_link->spec_ids));
man->free_spec_ids = new_free_ids;
man->free_spec_cnt = new_cnt;
}
}
return 0;
}
static void bpf_link_usdt_dealloc(struct bpf_link *link)
{
struct bpf_link_usdt *usdt_link = container_of(link, struct bpf_link_usdt, link);
free(usdt_link->spec_ids);
free(usdt_link->uprobes);
free(usdt_link);
}
static size_t specs_hash_fn(const void *key, void *ctx)
{
const char *s = key;
return str_hash(s);
}
static bool specs_equal_fn(const void *key1, const void *key2, void *ctx)
{
const char *s1 = key1;
const char *s2 = key2;
return strcmp(s1, s2) == 0;
}
static int allocate_spec_id(struct usdt_manager *man, struct hashmap *specs_hash,
struct bpf_link_usdt *link, struct usdt_target *target,
int *spec_id, bool *is_new)
{
void *tmp;
int err;
/* check if we already allocated spec ID for this spec string */
if (hashmap__find(specs_hash, target->spec_str, &tmp)) {
*spec_id = (long)tmp;
*is_new = false;
return 0;
}
/* otherwise it's a new ID that needs to be set up in specs map and
* returned back to usdt_manager when USDT link is detached
*/
tmp = libbpf_reallocarray(link->spec_ids, link->spec_cnt + 1, sizeof(*link->spec_ids));
if (!tmp)
return -ENOMEM;
link->spec_ids = tmp;
/* get next free spec ID, giving preference to free list, if not empty */
if (man->free_spec_cnt) {
*spec_id = man->free_spec_ids[man->free_spec_cnt - 1];
/* cache spec ID for current spec string for future lookups */
err = hashmap__add(specs_hash, target->spec_str, (void *)(long)*spec_id);
if (err)
return err;
man->free_spec_cnt--;
} else {
/* don't allocate spec ID bigger than what fits in specs map */
if (man->next_free_spec_id >= bpf_map__max_entries(man->specs_map))
return -E2BIG;
*spec_id = man->next_free_spec_id;
/* cache spec ID for current spec string for future lookups */
err = hashmap__add(specs_hash, target->spec_str, (void *)(long)*spec_id);
if (err)
return err;
man->next_free_spec_id++;
}
/* remember new spec ID in the link for later return back to free list on detach */
link->spec_ids[link->spec_cnt] = *spec_id;
link->spec_cnt++;
*is_new = true;
return 0;
}
struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct bpf_program *prog,
pid_t pid, const char *path,
const char *usdt_provider, const char *usdt_name,
__u64 usdt_cookie)
{
int i, fd, err, spec_map_fd, ip_map_fd;
LIBBPF_OPTS(bpf_uprobe_opts, opts);
struct hashmap *specs_hash = NULL;
struct bpf_link_usdt *link = NULL;
struct usdt_target *targets = NULL;
size_t target_cnt;
Elf *elf;
spec_map_fd = bpf_map__fd(man->specs_map);
ip_map_fd = bpf_map__fd(man->ip_to_spec_id_map);
/* TODO: perform path resolution similar to uprobe's */
fd = open(path, O_RDONLY);
if (fd < 0) {
err = -errno;
pr_warn("usdt: failed to open ELF binary '%s': %d\n", path, err);
return libbpf_err_ptr(err);
}
elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
if (!elf) {
err = -EBADF;
pr_warn("usdt: failed to parse ELF binary '%s': %s\n", path, elf_errmsg(-1));
goto err_out;
}
err = sanity_check_usdt_elf(elf, path);
if (err)
goto err_out;
/* normalize PID filter */
if (pid < 0)
pid = -1;
else if (pid == 0)
pid = getpid();
/* discover USDT in given binary, optionally limiting
* activations to a given PID, if pid > 0
*/
err = collect_usdt_targets(man, elf, path, pid, usdt_provider, usdt_name,
usdt_cookie, &targets, &target_cnt);
if (err <= 0) {
err = (err == 0) ? -ENOENT : err;
goto err_out;
}
specs_hash = hashmap__new(specs_hash_fn, specs_equal_fn, NULL);
if (IS_ERR(specs_hash)) {
err = PTR_ERR(specs_hash);
goto err_out;
}
link = calloc(1, sizeof(*link));
if (!link) {
err = -ENOMEM;
goto err_out;
}
link->usdt_man = man;
link->link.detach = &bpf_link_usdt_detach;
link->link.dealloc = &bpf_link_usdt_dealloc;
link->uprobes = calloc(target_cnt, sizeof(*link->uprobes));
if (!link->uprobes) {
err = -ENOMEM;
goto err_out;
}
for (i = 0; i < target_cnt; i++) {
struct usdt_target *target = &targets[i];
struct bpf_link *uprobe_link;
bool is_new;
int spec_id;
/* Spec ID can be either reused or newly allocated. If it is
* newly allocated, we'll need to fill out spec map, otherwise
* entire spec should be valid and can be just used by a new
* uprobe. We reuse spec when USDT arg spec is identical. We
* also never share specs between two different USDT
* attachments ("links"), so all the reused specs already
* share USDT cookie value implicitly.
*/
err = allocate_spec_id(man, specs_hash, link, target, &spec_id, &is_new);
if (err)
goto err_out;
if (is_new && bpf_map_update_elem(spec_map_fd, &spec_id, &target->spec, BPF_ANY)) {
err = -errno;
pr_warn("usdt: failed to set USDT spec #%d for '%s:%s' in '%s': %d\n",
spec_id, usdt_provider, usdt_name, path, err);
goto err_out;
}
if (!man->has_bpf_cookie &&
bpf_map_update_elem(ip_map_fd, &target->abs_ip, &spec_id, BPF_NOEXIST)) {
err = -errno;
if (err == -EEXIST) {
pr_warn("usdt: IP collision detected for spec #%d for '%s:%s' in '%s'\n",
spec_id, usdt_provider, usdt_name, path);
} else {
pr_warn("usdt: failed to map IP 0x%lx to spec #%d for '%s:%s' in '%s': %d\n",
target->abs_ip, spec_id, usdt_provider, usdt_name,
path, err);
}
goto err_out;
}
opts.ref_ctr_offset = target->sema_off;
opts.bpf_cookie = man->has_bpf_cookie ? spec_id : 0;
uprobe_link = bpf_program__attach_uprobe_opts(prog, pid, path,
target->rel_ip, &opts);
err = libbpf_get_error(uprobe_link);
if (err) {
pr_warn("usdt: failed to attach uprobe #%d for '%s:%s' in '%s': %d\n",
i, usdt_provider, usdt_name, path, err);
goto err_out;
}
link->uprobes[i].link = uprobe_link;
link->uprobes[i].abs_ip = target->abs_ip;
link->uprobe_cnt++;
}
free(targets);
hashmap__free(specs_hash);
elf_end(elf);
close(fd);
return &link->link;
err_out:
if (link)
bpf_link__destroy(&link->link);
free(targets);
hashmap__free(specs_hash);
if (elf)
elf_end(elf);
close(fd);
return libbpf_err_ptr(err);
}
/* Parse out USDT ELF note from '.note.stapsdt' section.
* Logic inspired by perf's code.
*/
static int parse_usdt_note(Elf *elf, const char *path, GElf_Nhdr *nhdr,
const char *data, size_t name_off, size_t desc_off,
struct usdt_note *note)
{
const char *provider, *name, *args;
long addrs[3];
size_t len;
/* sanity check USDT note name and type first */
if (strncmp(data + name_off, USDT_NOTE_NAME, nhdr->n_namesz) != 0)
return -EINVAL;
if (nhdr->n_type != USDT_NOTE_TYPE)
return -EINVAL;
/* sanity check USDT note contents ("description" in ELF terminology) */
len = nhdr->n_descsz;
data = data + desc_off;
/* +3 is the very minimum required to store three empty strings */
if (len < sizeof(addrs) + 3)
return -EINVAL;
/* get location, base, and semaphore addrs */
memcpy(&addrs, data, sizeof(addrs));
/* parse string fields: provider, name, args */
provider = data + sizeof(addrs);
name = (const char *)memchr(provider, '\0', data + len - provider);
if (!name) /* non-zero-terminated provider */
return -EINVAL;
name++;
if (name >= data + len || *name == '\0') /* missing or empty name */
return -EINVAL;
args = memchr(name, '\0', data + len - name);
if (!args) /* non-zero-terminated name */
return -EINVAL;
++args;
if (args >= data + len) /* missing arguments spec */
return -EINVAL;
note->provider = provider;
note->name = name;
if (*args == '\0' || *args == ':')
note->args = "";
else
note->args = args;
note->loc_addr = addrs[0];
note->base_addr = addrs[1];
note->sema_addr = addrs[2];
return 0;
}
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg);
static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note, __u64 usdt_cookie)
{
const char *s;
int len;
spec->usdt_cookie = usdt_cookie;
spec->arg_cnt = 0;
s = note->args;
while (s[0]) {
if (spec->arg_cnt >= USDT_MAX_ARG_CNT) {
pr_warn("usdt: too many USDT arguments (> %d) for '%s:%s' with args spec '%s'\n",
USDT_MAX_ARG_CNT, note->provider, note->name, note->args);
return -E2BIG;
}
len = parse_usdt_arg(s, spec->arg_cnt, &spec->args[spec->arg_cnt]);
if (len < 0)
return len;
s += len;
spec->arg_cnt++;
}
return 0;
}
/* Architecture-specific logic for parsing USDT argument location specs */
#if defined(__x86_64__) || defined(__i386__)
static int calc_pt_regs_off(const char *reg_name)
{
static struct {
const char *names[4];
size_t pt_regs_off;
} reg_map[] = {
#ifdef __x86_64__
#define reg_off(reg64, reg32) offsetof(struct pt_regs, reg64)
#else
#define reg_off(reg64, reg32) offsetof(struct pt_regs, reg32)
#endif
{ {"rip", "eip", "", ""}, reg_off(rip, eip) },
{ {"rax", "eax", "ax", "al"}, reg_off(rax, eax) },
{ {"rbx", "ebx", "bx", "bl"}, reg_off(rbx, ebx) },
{ {"rcx", "ecx", "cx", "cl"}, reg_off(rcx, ecx) },
{ {"rdx", "edx", "dx", "dl"}, reg_off(rdx, edx) },
{ {"rsi", "esi", "si", "sil"}, reg_off(rsi, esi) },
{ {"rdi", "edi", "di", "dil"}, reg_off(rdi, edi) },
{ {"rbp", "ebp", "bp", "bpl"}, reg_off(rbp, ebp) },
{ {"rsp", "esp", "sp", "spl"}, reg_off(rsp, esp) },
#undef reg_off
#ifdef __x86_64__
{ {"r8", "r8d", "r8w", "r8b"}, offsetof(struct pt_regs, r8) },
{ {"r9", "r9d", "r9w", "r9b"}, offsetof(struct pt_regs, r9) },
{ {"r10", "r10d", "r10w", "r10b"}, offsetof(struct pt_regs, r10) },
{ {"r11", "r11d", "r11w", "r11b"}, offsetof(struct pt_regs, r11) },
{ {"r12", "r12d", "r12w", "r12b"}, offsetof(struct pt_regs, r12) },
{ {"r13", "r13d", "r13w", "r13b"}, offsetof(struct pt_regs, r13) },
{ {"r14", "r14d", "r14w", "r14b"}, offsetof(struct pt_regs, r14) },
{ {"r15", "r15d", "r15w", "r15b"}, offsetof(struct pt_regs, r15) },
#endif
};
int i, j;
for (i = 0; i < ARRAY_SIZE(reg_map); i++) {
for (j = 0; j < ARRAY_SIZE(reg_map[i].names); j++) {
if (strcmp(reg_name, reg_map[i].names[j]) == 0)
return reg_map[i].pt_regs_off;
}
}
pr_warn("usdt: unrecognized register '%s'\n", reg_name);
return -ENOENT;
}
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{
char *reg_name = NULL;
int arg_sz, len, reg_off;
long off;
if (sscanf(arg_str, " %d @ %ld ( %%%m[^)] ) %n", &arg_sz, &off, &reg_name, &len) == 3) {
/* Memory dereference case, e.g., -4@-20(%rbp) */
arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off;
reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ %%%ms %n", &arg_sz, &reg_name, &len) == 2) {
/* Register read case, e.g., -4@%eax */
arg->arg_type = USDT_ARG_REG;
arg->val_off = 0;
reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ $%ld %n", &arg_sz, &off, &len) == 2) {
/* Constant value case, e.g., 4@$71 */
arg->arg_type = USDT_ARG_CONST;
arg->val_off = off;
arg->reg_off = 0;
} else {
pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
return -EINVAL;
}
arg->arg_signed = arg_sz < 0;
if (arg_sz < 0)
arg_sz = -arg_sz;
switch (arg_sz) {
case 1: case 2: case 4: case 8:
arg->arg_bitshift = 64 - arg_sz * 8;
break;
default:
pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
arg_num, arg_str, arg_sz);
return -EINVAL;
}
return len;
}
#elif defined(__s390x__)
/* Do not support __s390__ for now, since user_pt_regs is broken with -m31. */
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{
unsigned int reg;
int arg_sz, len;
long off;
if (sscanf(arg_str, " %d @ %ld ( %%r%u ) %n", &arg_sz, &off, &reg, &len) == 3) {
/* Memory dereference case, e.g., -2@-28(%r15) */
arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off;
if (reg > 15) {
pr_warn("usdt: unrecognized register '%%r%u'\n", reg);
return -EINVAL;
}
arg->reg_off = offsetof(user_pt_regs, gprs[reg]);
} else if (sscanf(arg_str, " %d @ %%r%u %n", &arg_sz, &reg, &len) == 2) {
/* Register read case, e.g., -8@%r0 */
arg->arg_type = USDT_ARG_REG;
arg->val_off = 0;
if (reg > 15) {
pr_warn("usdt: unrecognized register '%%r%u'\n", reg);
return -EINVAL;
}
arg->reg_off = offsetof(user_pt_regs, gprs[reg]);
} else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
/* Constant value case, e.g., 4@71 */
arg->arg_type = USDT_ARG_CONST;
arg->val_off = off;
arg->reg_off = 0;
} else {
pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
return -EINVAL;
}
arg->arg_signed = arg_sz < 0;
if (arg_sz < 0)
arg_sz = -arg_sz;
switch (arg_sz) {
case 1: case 2: case 4: case 8:
arg->arg_bitshift = 64 - arg_sz * 8;
break;
default:
pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
arg_num, arg_str, arg_sz);
return -EINVAL;
}
return len;
}
#elif defined(__aarch64__)
static int calc_pt_regs_off(const char *reg_name)
{
int reg_num;
if (sscanf(reg_name, "x%d", &reg_num) == 1) {
if (reg_num >= 0 && reg_num < 31)
return offsetof(struct user_pt_regs, regs[reg_num]);
} else if (strcmp(reg_name, "sp") == 0) {
return offsetof(struct user_pt_regs, sp);
}
pr_warn("usdt: unrecognized register '%s'\n", reg_name);
return -ENOENT;
}
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{
char reg_name[16];
int arg_sz, len, reg_off;
long off;
if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], %ld ] %n", &arg_sz, reg_name, &off, &len) == 3) {
/* Memory dereference case, e.g., -4@[sp, 96] */
arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off;
reg_off = calc_pt_regs_off(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) {
/* Memory dereference case, e.g., -4@[sp] */
arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = 0;
reg_off = calc_pt_regs_off(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
/* Constant value case, e.g., 4@5 */
arg->arg_type = USDT_ARG_CONST;
arg->val_off = off;
arg->reg_off = 0;
} else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
/* Register read case, e.g., -8@x4 */
arg->arg_type = USDT_ARG_REG;
arg->val_off = 0;
reg_off = calc_pt_regs_off(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else {
pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
return -EINVAL;
}
arg->arg_signed = arg_sz < 0;
if (arg_sz < 0)
arg_sz = -arg_sz;
switch (arg_sz) {
case 1: case 2: case 4: case 8:
arg->arg_bitshift = 64 - arg_sz * 8;
break;
default:
pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
arg_num, arg_str, arg_sz);
return -EINVAL;
}
return len;
}
#elif defined(__riscv)
static int calc_pt_regs_off(const char *reg_name)
{
static struct {
const char *name;
size_t pt_regs_off;
} reg_map[] = {
{ "ra", offsetof(struct user_regs_struct, ra) },
{ "sp", offsetof(struct user_regs_struct, sp) },
{ "gp", offsetof(struct user_regs_struct, gp) },
{ "tp", offsetof(struct user_regs_struct, tp) },
{ "a0", offsetof(struct user_regs_struct, a0) },
{ "a1", offsetof(struct user_regs_struct, a1) },
{ "a2", offsetof(struct user_regs_struct, a2) },
{ "a3", offsetof(struct user_regs_struct, a3) },
{ "a4", offsetof(struct user_regs_struct, a4) },
{ "a5", offsetof(struct user_regs_struct, a5) },
{ "a6", offsetof(struct user_regs_struct, a6) },
{ "a7", offsetof(struct user_regs_struct, a7) },
{ "s0", offsetof(struct user_regs_struct, s0) },
{ "s1", offsetof(struct user_regs_struct, s1) },
{ "s2", offsetof(struct user_regs_struct, s2) },
{ "s3", offsetof(struct user_regs_struct, s3) },
{ "s4", offsetof(struct user_regs_struct, s4) },
{ "s5", offsetof(struct user_regs_struct, s5) },
{ "s6", offsetof(struct user_regs_struct, s6) },
{ "s7", offsetof(struct user_regs_struct, s7) },
{ "s8", offsetof(struct user_regs_struct, rv_s8) },
{ "s9", offsetof(struct user_regs_struct, s9) },
{ "s10", offsetof(struct user_regs_struct, s10) },
{ "s11", offsetof(struct user_regs_struct, s11) },
{ "t0", offsetof(struct user_regs_struct, t0) },
{ "t1", offsetof(struct user_regs_struct, t1) },
{ "t2", offsetof(struct user_regs_struct, t2) },
{ "t3", offsetof(struct user_regs_struct, t3) },
{ "t4", offsetof(struct user_regs_struct, t4) },
{ "t5", offsetof(struct user_regs_struct, t5) },
{ "t6", offsetof(struct user_regs_struct, t6) },
};
int i;
for (i = 0; i < ARRAY_SIZE(reg_map); i++) {
if (strcmp(reg_name, reg_map[i].name) == 0)
return reg_map[i].pt_regs_off;
}
pr_warn("usdt: unrecognized register '%s'\n", reg_name);
return -ENOENT;
}
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{
char *reg_name = NULL;
int arg_sz, len, reg_off;
long off;
if (sscanf(arg_str, " %d @ %ld ( %m[a-z0-9] ) %n", &arg_sz, &off, &reg_name, &len) == 3) {
/* Memory dereference case, e.g., -8@-88(s0) */
arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off;
reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
/* Constant value case, e.g., 4@5 */
arg->arg_type = USDT_ARG_CONST;
arg->val_off = off;
arg->reg_off = 0;
} else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, &reg_name, &len) == 2) {
/* Register read case, e.g., -8@a1 */
arg->arg_type = USDT_ARG_REG;
arg->val_off = 0;
reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else {
pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
return -EINVAL;
}
arg->arg_signed = arg_sz < 0;
if (arg_sz < 0)
arg_sz = -arg_sz;
switch (arg_sz) {
case 1: case 2: case 4: case 8:
arg->arg_bitshift = 64 - arg_sz * 8;
break;
default:
pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
arg_num, arg_str, arg_sz);
return -EINVAL;
}
return len;
}
#else
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{
pr_warn("usdt: libbpf doesn't support USDTs on current architecture\n");
return -ENOTSUP;
}
#endif
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