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perf symbols: Get symbols for .plt.got for x86-64

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For x86_64, determine a symbol for .plt.got entries. That requires
computing the target offset and finding that in .rela.dyn, which in
turn means .rela.dyn needs to be sorted by offset.

Example:

  In this example, the GNU C Library is using .plt.got for malloc and
  free.

  Before:

    $ gcc --version
    gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0
    Copyright (C) 2021 Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.  There is NO
    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    $ perf record -e intel_pt//u uname
    Linux
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.027 MB perf.data ]
    $ perf script --itrace=be --ns -F-event,+addr,-period,-comm,-tid,-cpu > /tmp/cmp1.txt

  After:

    $ perf script --itrace=be --ns -F-event,+addr,-period,-comm,-tid,-cpu > /tmp/cmp2.txt
    $ diff /tmp/cmp1.txt /tmp/cmp2.txt | head -12
    15509,15510c15509,15510
    < 27046.755390907:      7f0b2943e3ab _nl_normalize_codeset+0x5b (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b29428380 offset_0x28380@plt+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    < 27046.755390907:      7f0b29428384 offset_0x28380@plt+0x4 (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b294a5120 malloc+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    ---
    > 27046.755390907:      7f0b2943e3ab _nl_normalize_codeset+0x5b (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b29428380 malloc@plt+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    > 27046.755390907:      7f0b29428384 malloc@plt+0x4 (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b294a5120 malloc+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    15821,15822c15821,15822
    < 27046.755394865:      7f0b2943850c _nl_load_locale_from_archive+0x5bc (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b29428370 offset_0x28370@plt+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    < 27046.755394865:      7f0b29428374 offset_0x28370@plt+0x4 (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b294a5460 cfree@GLIBC_2.2.5+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    ---
    > 27046.755394865:      7f0b2943850c _nl_load_locale_from_archive+0x5bc (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b29428370 free@plt+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)
    > 27046.755394865:      7f0b29428374 free@plt+0x4 (/usr/lib/x86_64-linux-gnu/libc.so.6) =>     7f0b294a5460 cfree@GLIBC_2.2.5+0x0 (/usr/lib/x86_64-linux-gnu/libc.so.6)

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230131131625.6964-10-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Adrian Hunter 2023-01-31 15:16:25 +02:00 committed by Arnaldo Carvalho de Melo
parent 51a188ad8c
commit ce4c8e7966
1 changed files with 157 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

161
tools/perf/util/symbol-elf.c
View File

@ -466,28 +466,181 @@ static bool machine_is_x86(GElf_Half e_machine)
return e_machine == EM_386 || e_machine == EM_X86_64;
}
struct rela_dyn {
GElf_Addr offset;
u32 sym_idx;
};
struct rela_dyn_info {
struct dso *dso;
Elf_Data *plt_got_data;
u32 nr_entries;
struct rela_dyn *sorted;
Elf_Data *dynsym_data;
Elf_Data *dynstr_data;
Elf_Data *rela_dyn_data;
};
static void exit_rela_dyn(struct rela_dyn_info *di)
{
free(di->sorted);
}
static int cmp_offset(const void *a, const void *b)
{
const struct rela_dyn *va = a;
const struct rela_dyn *vb = b;
return va->offset < vb->offset ? -1 : (va->offset > vb->offset ? 1 : 0);
}
static int sort_rela_dyn(struct rela_dyn_info *di)
{
u32 i, n;
di->sorted = calloc(di->nr_entries, sizeof(di->sorted[0]));
if (!di->sorted)
return -1;
/* Get data for sorting: the offset and symbol index */
for (i = 0, n = 0; i < di->nr_entries; i++) {
GElf_Rela rela;
u32 sym_idx;
gelf_getrela(di->rela_dyn_data, i, &rela);
sym_idx = GELF_R_SYM(rela.r_info);
if (sym_idx) {
di->sorted[n].sym_idx = sym_idx;
di->sorted[n].offset = rela.r_offset;
n += 1;
}
}
/* Sort by offset */
di->nr_entries = n;
qsort(di->sorted, n, sizeof(di->sorted[0]), cmp_offset);
return 0;
}
static void get_rela_dyn_info(Elf *elf, GElf_Ehdr *ehdr, struct rela_dyn_info *di, Elf_Scn *scn)
{
GElf_Shdr rela_dyn_shdr;
GElf_Shdr shdr;
di->plt_got_data = elf_getdata(scn, NULL);
scn = elf_section_by_name(elf, ehdr, &rela_dyn_shdr, ".rela.dyn", NULL);
if (!scn || !rela_dyn_shdr.sh_link || !rela_dyn_shdr.sh_entsize)
return;
di->nr_entries = rela_dyn_shdr.sh_size / rela_dyn_shdr.sh_entsize;
di->rela_dyn_data = elf_getdata(scn, NULL);
scn = elf_getscn(elf, rela_dyn_shdr.sh_link);
if (!scn || !gelf_getshdr(scn, &shdr) || !shdr.sh_link)
return;
di->dynsym_data = elf_getdata(scn, NULL);
di->dynstr_data = elf_getdata(elf_getscn(elf, shdr.sh_link), NULL);
if (!di->plt_got_data || !di->dynstr_data || !di->dynsym_data || !di->rela_dyn_data)
return;
/* Sort into offset order */
sort_rela_dyn(di);
}
/* Get instruction displacement from a plt entry for x86_64 */
static u32 get_x86_64_plt_disp(const u8 *p)
{
u8 endbr64[] = {0xf3, 0x0f, 0x1e, 0xfa};
int n = 0;
/* Skip endbr64 */
if (!memcmp(p, endbr64, sizeof(endbr64)))
n += sizeof(endbr64);
/* Skip bnd prefix */
if (p[n] == 0xf2)
n += 1;
/* jmp with 4-byte displacement */
if (p[n] == 0xff && p[n + 1] == 0x25) {
n += 2;
/* Also add offset from start of entry to end of instruction */
return n + 4 + le32toh(*(const u32 *)(p + n));
}
return 0;
}
static bool get_plt_got_name(GElf_Shdr *shdr, size_t i,
struct rela_dyn_info *di,
char *buf, size_t buf_sz)
{
struct rela_dyn vi, *vr;
const char *sym_name;
char *demangled;
GElf_Sym sym;
u32 disp;
if (!di->sorted)
return false;
disp = get_x86_64_plt_disp(di->plt_got_data->d_buf + i);
if (!disp)
return false;
/* Compute target offset of the .plt.got entry */
vi.offset = shdr->sh_offset + di->plt_got_data->d_off + i + disp;
/* Find that offset in .rela.dyn (sorted by offset) */
vr = bsearch(&vi, di->sorted, di->nr_entries, sizeof(di->sorted[0]), cmp_offset);
if (!vr)
return false;
/* Get the associated symbol */
gelf_getsym(di->dynsym_data, vr->sym_idx, &sym);
sym_name = elf_sym__name(&sym, di->dynstr_data);
demangled = demangle_sym(di->dso, 0, sym_name);
if (demangled != NULL)
sym_name = demangled;
snprintf(buf, buf_sz, "%s@plt", sym_name);
free(demangled);
return *sym_name;
}
static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
GElf_Ehdr *ehdr,
char *buf, size_t buf_sz)
{
struct rela_dyn_info di = { .dso = dso };
struct symbol *sym;
GElf_Shdr shdr;
Elf_Scn *scn;
int err = -1;
size_t i;
scn = elf_section_by_name(elf, ehdr, &shdr, ".plt.got", NULL);
if (!scn || !shdr.sh_entsize)
return 0;
if (ehdr->e_machine == EM_X86_64)
get_rela_dyn_info(elf, ehdr, &di, scn);
for (i = 0; i < shdr.sh_size; i += shdr.sh_entsize) {
snprintf(buf, buf_sz, "offset_%#" PRIx64 "@plt", (u64)shdr.sh_offset + i);
if (!get_plt_got_name(&shdr, i, &di, buf, buf_sz))
snprintf(buf, buf_sz, "offset_%#" PRIx64 "@plt", (u64)shdr.sh_offset + i);
sym = symbol__new(shdr.sh_offset + i, shdr.sh_entsize, STB_GLOBAL, STT_FUNC, buf);
if (!sym)
return -1;
goto out;
symbols__insert(&dso->symbols, sym);
}
return 0;
err = 0;
out:
exit_rela_dyn(&di);
return err;
}
/*