Messages in this thread Patch in this message | | | Date | Thu, 2 Feb 2023 16:41:17 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86 |
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Em Tue, Jan 31, 2023 at 03:16:24PM +0200, Adrian Hunter escreveu: > For x86, .plt.got is used, for example, when the address is taken of a > dynamically linked function. Start adding support by synthesizing a > symbol for each entry. A subsequent patch will attempt to get a better > name for the symbol. > > Example: > > Before: > > $ cat tstpltlib.c > void fn1(void) {} > void fn2(void) {} > void fn3(void) {} > void fn4(void) {} > $ cat tstpltgot.c > void fn1(void); > void fn2(void); > void fn3(void); > void fn4(void); > > void callfn(void (*fn)(void)) > { > fn(); > } > > int main() > { > fn4(); > fn1(); > callfn(fn3); > fn2(); > fn3(); > return 0; > } > $ 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. > $ gcc -Wall -Wextra -shared -o libtstpltlib.so tstpltlib.c > $ gcc -Wall -Wextra -o tstpltgot tstpltgot.c -L . -ltstpltlib -Wl,-rpath="$(pwd)" > $ readelf -SW tstpltgot | grep 'Name\|plt\|dyn' > [Nr] Name Type Address Off Size ES Flg Lk Inf Al > [ 6] .dynsym DYNSYM 00000000000003d8 0003d8 0000f0 18 A 7 1 8 > [ 7] .dynstr STRTAB 00000000000004c8 0004c8 0000c6 00 A 0 0 1 > [10] .rela.dyn RELA 00000000000005d8 0005d8 0000d8 18 A 6 0 8 > [11] .rela.plt RELA 00000000000006b0 0006b0 000048 18 AI 6 24 8 > [13] .plt PROGBITS 0000000000001020 001020 000040 10 AX 0 0 16 > [14] .plt.got PROGBITS 0000000000001060 001060 000020 10 AX 0 0 16 > [15] .plt.sec PROGBITS 0000000000001080 001080 000030 10 AX 0 0 16 > [23] .dynamic DYNAMIC 0000000000003d90 002d90 000210 10 WA 7 0 8 > $ perf record -e intel_pt//u --filter 'filter main @ ./tstpltgot , filter callfn @ ./tstpltgot' ./tstpltgot > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.011 MB perf.data ] > $ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso > 28393.810326915: tr strt 0 [unknown] => 562350baa1b2 main+0x0 > 28393.810326915: tr end call 562350baa1ba main+0x8 => 562350baa090 fn4@plt+0x0 > 28393.810326917: tr strt 0 [unknown] => 562350baa1bf main+0xd > 28393.810326917: tr end call 562350baa1bf main+0xd => 562350baa080 fn1@plt+0x0 > 28393.810326917: tr strt 0 [unknown] => 562350baa1c4 main+0x12 > 28393.810326917: call 562350baa1ce main+0x1c => 562350baa199 callfn+0x0 > 28393.810326917: tr end call 562350baa1ad callfn+0x14 => 7f607d36110f fn3+0x0 > 28393.810326922: tr strt 0 [unknown] => 562350baa1af callfn+0x16 > 28393.810326922: return 562350baa1b1 callfn+0x18 => 562350baa1d3 main+0x21 > 28393.810326922: tr end call 562350baa1d3 main+0x21 => 562350baa0a0 fn2@plt+0x0 > 28393.810326924: tr strt 0 [unknown] => 562350baa1d8 main+0x26 > 28393.810326924: tr end call 562350baa1d8 main+0x26 => 562350baa060 [unknown] <- call to fn3 via .plt.got > 28393.810326925: tr strt 0 [unknown] => 562350baa1dd main+0x2b > 28393.810326925: tr end return 562350baa1e3 main+0x31 => 7f607d029d90 __libc_start_call_main+0x80 > > After: > > $ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso > 28393.810326915: tr strt 0 [unknown] => 562350baa1b2 main+0x0 > 28393.810326915: tr end call 562350baa1ba main+0x8 => 562350baa090 fn4@plt+0x0 > 28393.810326917: tr strt 0 [unknown] => 562350baa1bf main+0xd > 28393.810326917: tr end call 562350baa1bf main+0xd => 562350baa080 fn1@plt+0x0 > 28393.810326917: tr strt 0 [unknown] => 562350baa1c4 main+0x12 > 28393.810326917: call 562350baa1ce main+0x1c => 562350baa199 callfn+0x0 > 28393.810326917: tr end call 562350baa1ad callfn+0x14 => 7f607d36110f fn3+0x0 > 28393.810326922: tr strt 0 [unknown] => 562350baa1af callfn+0x16 > 28393.810326922: return 562350baa1b1 callfn+0x18 => 562350baa1d3 main+0x21 > 28393.810326922: tr end call 562350baa1d3 main+0x21 => 562350baa0a0 fn2@plt+0x0 > 28393.810326924: tr strt 0 [unknown] => 562350baa1d8 main+0x26 > 28393.810326924: tr end call 562350baa1d8 main+0x26 => 562350baa060 offset_0x1060@plt+0x0 > 28393.810326925: tr strt 0 [unknown] => 562350baa1dd main+0x2b > 28393.810326925: tr end return 562350baa1e3 main+0x31 => 7f607d029d90 __libc_start_call_main+0x80 > > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> > --- > tools/perf/util/symbol-elf.c | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c > index 9e265a726418..254116d40e59 100644 > --- a/tools/perf/util/symbol-elf.c > +++ b/tools/perf/util/symbol-elf.c > @@ -466,6 +466,30 @@ static bool machine_is_x86(GElf_Half e_machine) > return e_machine == EM_386 || e_machine == EM_X86_64; > } > > +static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf, > + GElf_Ehdr *ehdr, > + char *buf, size_t buf_sz) > +{ > + struct symbol *sym; > + GElf_Shdr shdr; > + Elf_Scn *scn; > + size_t i; > + > + scn = elf_section_by_name(elf, ehdr, &shdr, ".plt.got", NULL); > + if (!scn || !shdr.sh_entsize) > + return 0; > + > + for (i = 0; i < shdr.sh_size; i += shdr.sh_entsize) { > + 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);
Had to apply the patch below with the following committer note:
Committer notes:
Fix build on 32-bit a arches where shdr.sh_offset is a uint32_t and on 64-bit whete it is uint64_t, so cast use PRIx64 and cast it to the 64-bit type, as done elsewhere in this same file.
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c index b149cfea73d0f422..41882ae8452e5091 100644 --- a/tools/perf/util/symbol-elf.c +++ b/tools/perf/util/symbol-elf.c @@ -631,7 +631,7 @@ static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf, for (i = 0; i < shdr.sh_size; i += shdr.sh_entsize) { if (!get_plt_got_name(&shdr, i, &di, buf, buf_sz)) - snprintf(buf, buf_sz, "offset_%#zx@plt", shdr.sh_offset + i); + 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) goto out; > + if (!sym) > + return -1; > + symbols__insert(&dso->symbols, sym); > + } > + > + return 0; > +} > + > /* > * We need to check if we have a .dynsym, so that we can handle the > * .plt, synthesizing its symbols, that aren't on the symtabs (be it > @@ -514,6 +538,11 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) > goto out_elf_end; > symbols__insert(&dso->symbols, plt_sym); > > + /* Only x86 has .plt.got */ > + if (machine_is_x86(ehdr.e_machine) && > + dso__synthesize_plt_got_symbols(dso, elf, &ehdr, sympltname, sizeof(sympltname))) > + goto out_elf_end; > + > /* Only x86 has .plt.sec */ > if (machine_is_x86(ehdr.e_machine) && > elf_section_by_name(elf, &ehdr, &plt_sec_shdr, ".plt.sec", NULL)) { > -- > 2.34.1 >
--
- Arnaldo
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