Messages in this thread | | | Date | Tue, 31 Jan 2023 12:17:56 +0200 | Subject | Re: [PATCH 9/9] perf symbols: Get symbols for .plt.got for x86-64 | From | Adrian Hunter <> |
| |
On 31/01/23 01:26, Namhyung Kim wrote: > On Fri, Jan 27, 2023 at 07:02:22PM +0200, Adrian Hunter wrote: >> 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) >> >> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> >> --- >> tools/perf/util/symbol-elf.c | 158 ++++++++++++++++++++++++++++++++++- >> 1 file changed, 154 insertions(+), 4 deletions(-) >> >> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c >> index 254116d40e59..4fc8e7fc10f4 100644 >> --- a/tools/perf/util/symbol-elf.c >> +++ b/tools/perf/util/symbol-elf.c >> @@ -466,28 +466,178 @@ 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) >> +{ >> + void *p = di->plt_got_data->d_buf + i; >> + u32 disp = get_x86_64_plt_disp(p); >> + struct rela_dyn vi, *vr; >> + const char *sym_name; >> + char *demangled; >> + GElf_Sym sym; >> + >> + if (!di->sorted || !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); > > What about EM_386? Now I'm seeing segfaults on 32 bit test programs > with .plt.got section.
Thanks for looking at this.
Looks like a late change in get_plt_got_name() did not get tested for 32-bit. It should be checking di->sorted first. EM_386 is not supported by this logic.
I will send a V2
> > Thanks, > Namhyung > > >> + >> for (i = 0; i < shdr.sh_size; i += shdr.sh_entsize) { >> - snprintf(buf, buf_sz, "offset_%#zx@plt", shdr.sh_offset + i); >> + if (!get_plt_got_name(&shdr, i, &di, buf, buf_sz)) >> + snprintf(buf, buf_sz, "offset_%#zx@plt", 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; >> } >> >> /* >> -- >> 2.34.1 >> >>
| |