diff options
author | Adrian Hunter <adrian.hunter@intel.com> | 2023-01-31 16:16:23 +0300 |
---|---|---|
committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2023-02-02 03:51:51 +0300 |
commit | a1ab12856f27f37465daf640dce8df044ecbc64b (patch) | |
tree | 671cb1c5ac288b552433709823129106aa9835d8 /tools/perf | |
parent | 60fbb3e49abe8421b677d5eee32fe7fb27b05e3b (diff) | |
download | linux-a1ab12856f27f37465daf640dce8df044ecbc64b.tar.xz |
perf symbols: Allow for static executables with .plt
A statically linked executable can have a .plt due to IFUNCs, in which
case .symtab is used not .dynsym. Check the section header link to see
if that is the case, and then use symtab instead.
Example:
Before:
$ cat tstifunc.c
#include <stdio.h>
void thing1(void)
{
printf("thing1\n");
}
void thing2(void)
{
printf("thing2\n");
}
typedef void (*thing_fn_t)(void);
thing_fn_t thing_ifunc(void)
{
int x;
if (x & 1)
return thing2;
return thing1;
}
void thing(void) __attribute__ ((ifunc ("thing_ifunc")));
int main()
{
thing();
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 -static -Wall -Wextra -Wno-uninitialized -o tstifuncstatic tstifunc.c
$ readelf -SW tstifuncstatic | grep 'Name\|plt\|dyn'
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 4] .rela.plt RELA 00000000004002e8 0002e8 000258 18 AI 29 20 8
[ 6] .plt PROGBITS 0000000000401020 001020 000190 00 AX 0 0 16
[20] .got.plt PROGBITS 00000000004c5000 0c4000 0000e0 08 WA 0 0 8
$ perf record -e intel_pt//u --filter 'filter main @ ./tstifuncstatic' ./tstifuncstatic
thing1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.008 MB perf.data ]
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
15786.690189535: tr strt 0 [unknown] => 4017cd main+0x0
15786.690189535: tr end call 4017d5 main+0x8 => 401170 [unknown]
15786.690197660: tr strt 0 [unknown] => 4017da main+0xd
15786.690197660: tr end return 4017e0 main+0x13 => 401c1a __libc_start_call_main+0x6a
After:
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
15786.690189535: tr strt 0 [unknown] => 4017cd main+0x0
15786.690189535: tr end call 4017d5 main+0x8 => 401170 thing_ifunc@plt+0x0
15786.690197660: tr strt 0 [unknown] => 4017da main+0xd
15786.690197660: tr end return 4017e0 main+0x13 => 401c1a __libc_start_call_main+0x6a
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/20230131131625.6964-8-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf')
-rw-r--r-- | tools/perf/util/symbol-elf.c | 30 | ||||
-rw-r--r-- | tools/perf/util/symsrc.h | 1 |
2 files changed, 21 insertions, 10 deletions
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c index 8f7802097c72..9e265a726418 100644 --- a/tools/perf/util/symbol-elf.c +++ b/tools/perf/util/symbol-elf.c @@ -483,7 +483,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) GElf_Shdr shdr_rel_plt, shdr_dynsym; Elf_Data *syms, *symstrs; Elf_Scn *scn_plt_rel, *scn_symstrs, *scn_dynsym; - size_t dynsym_idx; GElf_Ehdr ehdr; char sympltname[1024]; Elf *elf; @@ -530,13 +529,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) lazy_plt = true; } - scn_dynsym = ss->dynsym; - shdr_dynsym = ss->dynshdr; - dynsym_idx = ss->dynsym_idx; - - if (scn_dynsym == NULL) - return 0; - scn_plt_rel = elf_section_by_name(elf, &ehdr, &shdr_rel_plt, ".rela.plt", NULL); if (scn_plt_rel == NULL) { @@ -550,8 +542,25 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) shdr_rel_plt.sh_type != SHT_REL) return 0; - if (shdr_rel_plt.sh_link != dynsym_idx) + if (!shdr_rel_plt.sh_link) + return 0; + + if (shdr_rel_plt.sh_link == ss->dynsym_idx) { + scn_dynsym = ss->dynsym; + shdr_dynsym = ss->dynshdr; + } else if (shdr_rel_plt.sh_link == ss->symtab_idx) { + /* + * A static executable can have a .plt due to IFUNCs, in which + * case .symtab is used not .dynsym. + */ + scn_dynsym = ss->symtab; + shdr_dynsym = ss->symshdr; + } else { goto out_elf_end; + } + + if (!scn_dynsym) + return 0; /* * Fetch the relocation section to find the idxes to the GOT @@ -1077,8 +1086,9 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name, ss->is_64_bit = (gelf_getclass(elf) == ELFCLASS64); + ss->symtab_idx = 0; ss->symtab = elf_section_by_name(elf, &ehdr, &ss->symshdr, ".symtab", - NULL); + &ss->symtab_idx); if (ss->symshdr.sh_type != SHT_SYMTAB) ss->symtab = NULL; diff --git a/tools/perf/util/symsrc.h b/tools/perf/util/symsrc.h index 2665b4bde751..edf82028c9e6 100644 --- a/tools/perf/util/symsrc.h +++ b/tools/perf/util/symsrc.h @@ -26,6 +26,7 @@ struct symsrc { GElf_Shdr opdshdr; Elf_Scn *symtab; + size_t symtab_idx; GElf_Shdr symshdr; Elf_Scn *dynsym; |