* [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86
@ 2023-01-31 13:16 Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 1/9] perf symbols: Correct plt entry sizes " Adrian Hunter
` (9 more replies)
0 siblings, 10 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
Hi
This is version 2 of the second of 2 patchsets to improve
dso__synthesize_plt_symbols().
This patchset focuses on getting rid of unknown symbols that show up in
Intel PT traces.
x86 has 2 more plt's, namely .plt.sec and .plt.got, so support is added for
synthesizing symbols for them. Special handing is needed for IFUNC symbols,
and it is also possible to have a .plt for static executables, so support is
added for that.
Changes in V2:
perf symbols: Add support for x86 .plt.sec
Amend commit message and example about -z plt
perf symbols: Get symbols for .plt.got for x86-64
Fix get_plt_got_name() not to segfault with EM_386
Adrian Hunter (9):
perf symbols: Correct plt entry sizes for x86
perf symbols: Add support for x86 .plt.sec
perf symbols: Sort plt relocations for x86
perf symbols: Record whether a symbol is an alias for an IFUNC symbol
perf symbols: Add support for IFUNC symbols for x86_64
perf symbols: Allow for .plt without header
perf symbols: Allow for static executables with .plt
perf symbols: Start adding support for .plt.got for x86
perf symbols: Get symbols for .plt.got for x86-64
tools/perf/util/symbol-elf.c | 365 ++++++++++++++++++++++++++++++++++++++++---
tools/perf/util/symbol.c | 4 +
tools/perf/util/symbol.h | 2 +
tools/perf/util/symsrc.h | 1 +
4 files changed, 350 insertions(+), 22 deletions(-)
Regards
Adrian
^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH V2 1/9] perf symbols: Correct plt entry sizes for x86
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 2/9] perf symbols: Add support for x86 .plt.sec Adrian Hunter
` (8 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
In 32-bit executables the .plt entry size can be set to 4 when it is really
16. In fact the only sizes used for x86 (32 or 64 bit) are 8 or 16, so
check for those and, if not, use the alignment to choose which it is.
Example on Ubuntu 22.04 gcc 11.3:
Before:
$ cat tstpltlib.c
void fn1(void) {}
void fn2(void) {}
void fn3(void) {}
void fn4(void) {}
$ cat tstplt.c
void fn1(void);
void fn2(void);
void fn3(void);
void fn4(void);
int main()
{
fn4();
fn1();
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 -m32 -Wall -Wextra -shared -o libtstpltlib32.so tstpltlib.c
$ gcc -m32 -Wall -Wextra -o tstplt32 tstplt.c -L . -ltstpltlib32 -Wl,-rpath=$(pwd)
$ perf record -e intel_pt//u --filter 'filter main @ ./tstplt32' ./tstplt32
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.011 MB perf.data ]
$ readelf -SW tstplt32 | grep 'plt\|Name'
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[10] .rel.plt REL 0000041c 00041c 000028 08 AI 5 22 4
[12] .plt PROGBITS 00001030 001030 000060 04 AX 0 0 16 <- ES is 0x04, should be 0x10
[13] .plt.got PROGBITS 00001090 001090 000008 08 AX 0 0 8
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
17894.383903029: tr strt 0 [unknown] => 565b81cd main+0x0
17894.383903029: tr end call 565b81d4 main+0x7 => 565b80d0 __x86.get_pc_thunk.bx+0x0
17894.383903031: tr strt 0 [unknown] => 565b81d9 main+0xc
17894.383903031: tr end call 565b81df main+0x12 => 565b8070 [unknown]
17894.383903032: tr strt 0 [unknown] => 565b81e4 main+0x17
17894.383903032: tr end call 565b81e4 main+0x17 => 565b8050 [unknown]
17894.383903033: tr strt 0 [unknown] => 565b81e9 main+0x1c
17894.383903033: tr end call 565b81e9 main+0x1c => 565b8080 [unknown]
17894.383903033: tr strt 0 [unknown] => 565b81ee main+0x21
17894.383903033: tr end call 565b81ee main+0x21 => 565b8060 [unknown]
17894.383903237: tr strt 0 [unknown] => 565b81f3 main+0x26
17894.383903237: tr end return 565b81fc main+0x2f => f7c21519 [unknown]
After:
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
17894.383903029: tr strt 0 [unknown] => 565b81cd main+0x0
17894.383903029: tr end call 565b81d4 main+0x7 => 565b80d0 __x86.get_pc_thunk.bx+0x0
17894.383903031: tr strt 0 [unknown] => 565b81d9 main+0xc
17894.383903031: tr end call 565b81df main+0x12 => 565b8070 fn4@plt+0x0
17894.383903032: tr strt 0 [unknown] => 565b81e4 main+0x17
17894.383903032: tr end call 565b81e4 main+0x17 => 565b8050 fn1@plt+0x0
17894.383903033: tr strt 0 [unknown] => 565b81e9 main+0x1c
17894.383903033: tr end call 565b81e9 main+0x1c => 565b8080 fn2@plt+0x0
17894.383903033: tr strt 0 [unknown] => 565b81ee main+0x21
17894.383903033: tr end call 565b81ee main+0x21 => 565b8060 fn3@plt+0x0
17894.383903237: tr strt 0 [unknown] => 565b81f3 main+0x26
17894.383903237: tr end return 565b81fc main+0x2f => f7c21519 [unknown]
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index aa62735aea7b..9328c162d68f 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -360,14 +360,23 @@ static bool get_plt_sizes(struct dso *dso, GElf_Ehdr *ehdr, GElf_Shdr *shdr_plt,
*plt_header_size = 128;
*plt_entry_size = 32;
return true;
+ case EM_386:
+ case EM_X86_64:
+ *plt_entry_size = shdr_plt->sh_entsize;
+ /* Size is 8 or 16, if not, assume alignment indicates size */
+ if (*plt_entry_size != 8 && *plt_entry_size != 16)
+ *plt_entry_size = shdr_plt->sh_addralign == 8 ? 8 : 16;
+ *plt_header_size = *plt_entry_size;
+ break;
default: /* FIXME: s390/alpha/mips/parisc/poperpc/sh/xtensa need to be checked */
*plt_header_size = shdr_plt->sh_entsize;
*plt_entry_size = shdr_plt->sh_entsize;
- if (*plt_entry_size)
- return true;
- pr_debug("Missing PLT entry size for %s\n", dso->long_name);
- return false;
+ break;
}
+ if (*plt_entry_size)
+ return true;
+ pr_debug("Missing PLT entry size for %s\n", dso->long_name);
+ return false;
}
/*
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 2/9] perf symbols: Add support for x86 .plt.sec
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 1/9] perf symbols: Correct plt entry sizes " Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 3/9] perf symbols: Sort plt relocations for x86 Adrian Hunter
` (7 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
The section .plt.sec was originally added for MPX and was first called
.plt.bnd. While MPX has been deprecated, .plt.sec is now also used for IBT.
On x86_64, IBT may be enabled by default, but can be switched off
using gcc option -fcf-protection=none, or switched on by -z ibt or
-z ibtplt. On 32-bit, option -z ibt or -z ibtplt will enable IBT.
With .plt.sec, calls are made into .plt.sec instead of .plt, so it
makes more sense to put the symbols there instead of .plt. A notable
difference is that .plt.sec does not have a header entry.
For x86, when synthesizing symbols for plt, use offset and entry size of
.plt.sec instead of .plt when there is a .plt.sec section.
Example on Ubuntu 22.04 gcc 11.3:
Before:
$ cat tstpltlib.c
void fn1(void) {}
void fn2(void) {}
void fn3(void) {}
void fn4(void) {}
$ cat tstplt.c
void fn1(void);
void fn2(void);
void fn3(void);
void fn4(void);
int main()
{
fn4();
fn1();
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 -z ibt -o tstplt tstplt.c -L . -ltstpltlib -Wl,-rpath=$(pwd)
$ readelf -SW tstplt | grep 'plt\|Name'
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[11] .rela.plt RELA 0000000000000698 000698 000060 18 AI 6 24 8
[13] .plt PROGBITS 0000000000001020 001020 000050 10 AX 0 0 16
[14] .plt.got PROGBITS 0000000000001070 001070 000010 10 AX 0 0 16
[15] .plt.sec PROGBITS 0000000000001080 001080 000040 10 AX 0 0 16
$ perf record -e intel_pt//u --filter 'filter main @ ./tstplt' ./tstplt
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.015 MB perf.data ]
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
38970.522546686: tr strt 0 [unknown] => 55fc222a81a9 main+0x0
38970.522546686: tr end call 55fc222a81b1 main+0x8 => 55fc222a80a0 [unknown]
38970.522546687: tr strt 0 [unknown] => 55fc222a81b6 main+0xd
38970.522546687: tr end call 55fc222a81b6 main+0xd => 55fc222a8080 [unknown]
38970.522546688: tr strt 0 [unknown] => 55fc222a81bb main+0x12
38970.522546688: tr end call 55fc222a81bb main+0x12 => 55fc222a80b0 [unknown]
38970.522546688: tr strt 0 [unknown] => 55fc222a81c0 main+0x17
38970.522546688: tr end call 55fc222a81c0 main+0x17 => 55fc222a8090 [unknown]
38970.522546689: tr strt 0 [unknown] => 55fc222a81c5 main+0x1c
38970.522546894: tr end return 55fc222a81cb main+0x22 => 7f3a4dc29d90 __libc_start_call_main+0x80
After:
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
38970.522546686: tr strt 0 [unknown] => 55fc222a81a9 main+0x0
38970.522546686: tr end call 55fc222a81b1 main+0x8 => 55fc222a80a0 fn4@plt+0x0
38970.522546687: tr strt 0 [unknown] => 55fc222a81b6 main+0xd
38970.522546687: tr end call 55fc222a81b6 main+0xd => 55fc222a8080 fn1@plt+0x0
38970.522546688: tr strt 0 [unknown] => 55fc222a81bb main+0x12
38970.522546688: tr end call 55fc222a81bb main+0x12 => 55fc222a80b0 fn2@plt+0x0
38970.522546688: tr strt 0 [unknown] => 55fc222a81c0 main+0x17
38970.522546688: tr end call 55fc222a81c0 main+0x17 => 55fc222a8090 fn3@plt+0x0
38970.522546689: tr strt 0 [unknown] => 55fc222a81c5 main+0x1c
38970.522546894: tr end return 55fc222a81cb main+0x22 => 7f3a4dc29d90 __libc_start_call_main+0x80
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 30 +++++++++++++++++++++++-------
1 file changed, 23 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 9328c162d68f..bb1b5cb3ff12 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -379,6 +379,11 @@ static bool get_plt_sizes(struct dso *dso, GElf_Ehdr *ehdr, GElf_Shdr *shdr_plt,
return false;
}
+static bool machine_is_x86(GElf_Half e_machine)
+{
+ return e_machine == EM_386 || e_machine == EM_X86_64;
+}
+
/*
* 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
@@ -391,8 +396,8 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
uint32_t nr_rel_entries, idx;
GElf_Sym sym;
u64 plt_offset, plt_header_size, plt_entry_size;
- GElf_Shdr shdr_plt;
- struct symbol *f;
+ GElf_Shdr shdr_plt, plt_sec_shdr;
+ struct symbol *f, *plt_sym;
GElf_Shdr shdr_rel_plt, shdr_dynsym;
Elf_Data *syms, *symstrs;
Elf_Scn *scn_plt_rel, *scn_symstrs, *scn_dynsym;
@@ -422,10 +427,23 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
return 0;
/* Add a symbol for .plt header */
- f = symbol__new(shdr_plt.sh_offset, plt_header_size, STB_GLOBAL, STT_FUNC, ".plt");
- if (!f)
+ plt_sym = symbol__new(shdr_plt.sh_offset, plt_header_size, STB_GLOBAL, STT_FUNC, ".plt");
+ if (!plt_sym)
goto out_elf_end;
- symbols__insert(&dso->symbols, f);
+ symbols__insert(&dso->symbols, plt_sym);
+
+ /* Only x86 has .plt.sec */
+ if (machine_is_x86(ehdr.e_machine) &&
+ elf_section_by_name(elf, &ehdr, &plt_sec_shdr, ".plt.sec", NULL)) {
+ if (!get_plt_sizes(dso, &ehdr, &plt_sec_shdr, &plt_header_size, &plt_entry_size))
+ return 0;
+ /* Extend .plt symbol to entire .plt */
+ plt_sym->end = plt_sym->start + shdr_plt.sh_size;
+ /* Use .plt.sec offset */
+ plt_offset = plt_sec_shdr.sh_offset;
+ } else {
+ plt_offset = shdr_plt.sh_offset + plt_header_size;
+ }
scn_dynsym = ss->dynsym;
shdr_dynsym = ss->dynshdr;
@@ -474,8 +492,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
goto out_elf_end;
nr_rel_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;
- plt_offset = shdr_plt.sh_offset;
- plt_offset += plt_header_size;
ri.is_rela = shdr_rel_plt.sh_type == SHT_RELA;
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 3/9] perf symbols: Sort plt relocations for x86
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 1/9] perf symbols: Correct plt entry sizes " Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 2/9] perf symbols: Add support for x86 .plt.sec Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 4/9] perf symbols: Record whether a symbol is an alias for an IFUNC symbol Adrian Hunter
` (6 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
For x86, with the addition of IFUNCs, relocation information becomes
disordered with respect to plt. Correct that by sorting the relocations by
offset.
Example:
Before:
$ cat tstpltlib.c
void fn1(void) {}
void fn2(void) {}
void fn3(void) {}
void fn4(void) {}
$ cat tstpltifunc.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")));
void fn1(void);
void fn2(void);
void fn3(void);
void fn4(void);
int main()
{
fn4();
fn1();
thing();
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 -Wno-uninitialized -o tstpltifunc tstpltifunc.c -L . -ltstpltlib -Wl,-rpath="$(pwd)"
$ readelf -rW tstpltifunc | grep -A99 plt
Relocation section '.rela.plt' at offset 0x738 contains 8 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000003f98 0000000300000007 R_X86_64_JUMP_SLOT 0000000000000000 puts@GLIBC_2.2.5 + 0
0000000000003fa8 0000000400000007 R_X86_64_JUMP_SLOT 0000000000000000 __stack_chk_fail@GLIBC_2.4 + 0
0000000000003fb0 0000000500000007 R_X86_64_JUMP_SLOT 0000000000000000 fn1 + 0
0000000000003fb8 0000000600000007 R_X86_64_JUMP_SLOT 0000000000000000 fn3 + 0
0000000000003fc0 0000000800000007 R_X86_64_JUMP_SLOT 0000000000000000 fn4 + 0
0000000000003fc8 0000000900000007 R_X86_64_JUMP_SLOT 0000000000000000 fn2 + 0
0000000000003fd0 0000000b00000007 R_X86_64_JUMP_SLOT 0000000000000000 getrandom@GLIBC_2.25 + 0
0000000000003fa0 0000000000000025 R_X86_64_IRELATIVE 125d
$ perf record -e intel_pt//u --filter 'filter main @ ./tstpltifunc' ./tstpltifunc
thing2
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.029 MB perf.data ]
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
20417.302513948: tr strt 0 [unknown] => 5629a74892be main+0x0
20417.302513948: tr end call 5629a74892c6 main+0x8 => 5629a7489110 fn2@plt+0x0
20417.302513949: tr strt 0 [unknown] => 5629a74892cb main+0xd
20417.302513949: tr end call 5629a74892cb main+0xd => 5629a74890f0 fn3@plt+0x0
20417.302513950: tr strt 0 [unknown] => 5629a74892d0 main+0x12
20417.302513950: tr end call 5629a74892d0 main+0x12 => 5629a74890d0 __stack_chk_fail@plt+0x0
20417.302528114: tr strt 0 [unknown] => 5629a74892d5 main+0x17
20417.302528114: tr end call 5629a74892d5 main+0x17 => 5629a7489120 getrandom@plt+0x0
20417.302528115: tr strt 0 [unknown] => 5629a74892da main+0x1c
20417.302528115: tr end call 5629a74892da main+0x1c => 5629a7489100 fn4@plt+0x0
20417.302528115: tr strt 0 [unknown] => 5629a74892df main+0x21
20417.302528115: tr end return 5629a74892e5 main+0x27 => 7ff14da29d90 __libc_start_call_main+0x80
After:
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
20417.302513948: tr strt 0 [unknown] => 5629a74892be main+0x0
20417.302513948: tr end call 5629a74892c6 main+0x8 => 5629a7489110 fn4@plt+0x0
20417.302513949: tr strt 0 [unknown] => 5629a74892cb main+0xd
20417.302513949: tr end call 5629a74892cb main+0xd => 5629a74890f0 fn1@plt+0x0
20417.302513950: tr strt 0 [unknown] => 5629a74892d0 main+0x12
20417.302513950: tr end call 5629a74892d0 main+0x12 => 5629a74890d0 offset_0x10d0@plt+0x0
20417.302528114: tr strt 0 [unknown] => 5629a74892d5 main+0x17
20417.302528114: tr end call 5629a74892d5 main+0x17 => 5629a7489120 fn2@plt+0x0
20417.302528115: tr strt 0 [unknown] => 5629a74892da main+0x1c
20417.302528115: tr end call 5629a74892da main+0x1c => 5629a7489100 fn3@plt+0x0
20417.302528115: tr strt 0 [unknown] => 5629a74892df main+0x21
20417.302528115: tr end return 5629a74892e5 main+0x27 => 7ff14da29d90 __libc_start_call_main+0x80
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 60 ++++++++++++++++++++++++++++++++++--
1 file changed, 57 insertions(+), 3 deletions(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index bb1b5cb3ff12..07cfcf8f40e3 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -324,6 +324,8 @@ static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
}
struct rel_info {
+ u32 nr_entries;
+ u32 *sorted;
bool is_rela;
Elf_Data *reldata;
GElf_Rela rela;
@@ -332,6 +334,7 @@ struct rel_info {
static u32 get_rel_symidx(struct rel_info *ri, u32 idx)
{
+ idx = ri->sorted ? ri->sorted[idx] : idx;
if (ri->is_rela) {
gelf_getrela(ri->reldata, idx, &ri->rela);
return GELF_R_SYM(ri->rela.r_info);
@@ -340,6 +343,49 @@ static u32 get_rel_symidx(struct rel_info *ri, u32 idx)
return GELF_R_SYM(ri->rel.r_info);
}
+static u64 get_rel_offset(struct rel_info *ri, u32 x)
+{
+ if (ri->is_rela) {
+ GElf_Rela rela;
+
+ gelf_getrela(ri->reldata, x, &rela);
+ return rela.r_offset;
+ } else {
+ GElf_Rel rel;
+
+ gelf_getrel(ri->reldata, x, &rel);
+ return rel.r_offset;
+ }
+}
+
+static int rel_cmp(const void *a, const void *b, void *r)
+{
+ struct rel_info *ri = r;
+ u64 a_offset = get_rel_offset(ri, *(const u32 *)a);
+ u64 b_offset = get_rel_offset(ri, *(const u32 *)b);
+
+ return a_offset < b_offset ? -1 : (a_offset > b_offset ? 1 : 0);
+}
+
+static int sort_rel(struct rel_info *ri)
+{
+ size_t sz = sizeof(ri->sorted[0]);
+ u32 i;
+
+ ri->sorted = calloc(ri->nr_entries, sz);
+ if (!ri->sorted)
+ return -1;
+ for (i = 0; i < ri->nr_entries; i++)
+ ri->sorted[i] = i;
+ qsort_r(ri->sorted, ri->nr_entries, sz, rel_cmp, ri);
+ return 0;
+}
+
+static void exit_rel(struct rel_info *ri)
+{
+ free(ri->sorted);
+}
+
static bool get_plt_sizes(struct dso *dso, GElf_Ehdr *ehdr, GElf_Shdr *shdr_plt,
u64 *plt_header_size, u64 *plt_entry_size)
{
@@ -393,7 +439,7 @@ static bool machine_is_x86(GElf_Half e_machine)
*/
int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
{
- uint32_t nr_rel_entries, idx;
+ uint32_t idx;
GElf_Sym sym;
u64 plt_offset, plt_header_size, plt_entry_size;
GElf_Shdr shdr_plt, plt_sec_shdr;
@@ -491,11 +537,18 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
if (symstrs->d_size == 0)
goto out_elf_end;
- nr_rel_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;
+ ri.nr_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;
ri.is_rela = shdr_rel_plt.sh_type == SHT_RELA;
- for (idx = 0; idx < nr_rel_entries; idx++) {
+ /*
+ * x86 doesn't insert IFUNC relocations in .plt order, so sort to get
+ * back in order.
+ */
+ if (machine_is_x86(ehdr.e_machine) && sort_rel(&ri))
+ goto out_elf_end;
+
+ for (idx = 0; idx < ri.nr_entries; idx++) {
const char *elf_name = NULL;
char *demangled = NULL;
@@ -523,6 +576,7 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
err = 0;
out_elf_end:
+ exit_rel(&ri);
if (err == 0)
return nr;
pr_debug("%s: problems reading %s PLT info.\n",
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 4/9] perf symbols: Record whether a symbol is an alias for an IFUNC symbol
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (2 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 3/9] perf symbols: Sort plt relocations for x86 Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 5/9] perf symbols: Add support for IFUNC symbols for x86_64 Adrian Hunter
` (5 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
To assist with synthesizing plt symbols for IFUNCs, record whether a
symbol is an alias of an IFUNC symbol.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol.c | 4 ++++
tools/perf/util/symbol.h | 2 ++
2 files changed, 6 insertions(+)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index a024f06f75d8..d05727fcb30d 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -201,10 +201,14 @@ void symbols__fixup_duplicate(struct rb_root_cached *symbols)
continue;
if (choose_best_symbol(curr, next) == SYMBOL_A) {
+ if (next->type == STT_GNU_IFUNC)
+ curr->ifunc_alias = true;
rb_erase_cached(&next->rb_node, symbols);
symbol__delete(next);
goto again;
} else {
+ if (curr->type == STT_GNU_IFUNC)
+ next->ifunc_alias = true;
nd = rb_next(&curr->rb_node);
rb_erase_cached(&curr->rb_node, symbols);
symbol__delete(curr);
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 2fdeb22bd02f..7558735543c2 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -64,6 +64,8 @@ struct symbol {
u8 inlined:1;
/** Has symbol__annotate2 been performed. */
u8 annotate2:1;
+ /** Symbol is an alias of an STT_GNU_IFUNC */
+ u8 ifunc_alias:1;
/** Architecture specific. Unused except on PPC where it holds st_other. */
u8 arch_sym;
/** The name of length namelen associated with the symbol. */
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 5/9] perf symbols: Add support for IFUNC symbols for x86_64
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (3 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 4/9] perf symbols: Record whether a symbol is an alias for an IFUNC symbol Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 6/9] perf symbols: Allow for .plt without header Adrian Hunter
` (4 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
For x86_64, the GNU linker is putting IFUNC information in the relocation
addend, so use it to try to find a symbol for plt entries that refer to
IFUNCs.
Example:
Before:
$ cat tstpltlib.c
void fn1(void) {}
void fn2(void) {}
void fn3(void) {}
void fn4(void) {}
$ cat tstpltifunc.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")));
void fn1(void);
void fn2(void);
void fn3(void);
void fn4(void);
int main()
{
fn4();
fn1();
thing();
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 -Wno-uninitialized -o tstpltifunc tstpltifunc.c -L . -ltstpltlib -Wl,-rpath="$(pwd)"
$ readelf -rW tstpltifunc | grep -A99 plt
Relocation section '.rela.plt' at offset 0x738 contains 8 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000003f98 0000000300000007 R_X86_64_JUMP_SLOT 0000000000000000 puts@GLIBC_2.2.5 + 0
0000000000003fa8 0000000400000007 R_X86_64_JUMP_SLOT 0000000000000000 __stack_chk_fail@GLIBC_2.4 + 0
0000000000003fb0 0000000500000007 R_X86_64_JUMP_SLOT 0000000000000000 fn1 + 0
0000000000003fb8 0000000600000007 R_X86_64_JUMP_SLOT 0000000000000000 fn3 + 0
0000000000003fc0 0000000800000007 R_X86_64_JUMP_SLOT 0000000000000000 fn4 + 0
0000000000003fc8 0000000900000007 R_X86_64_JUMP_SLOT 0000000000000000 fn2 + 0
0000000000003fd0 0000000b00000007 R_X86_64_JUMP_SLOT 0000000000000000 getrandom@GLIBC_2.25 + 0
0000000000003fa0 0000000000000025 R_X86_64_IRELATIVE 125d
$ perf record -e intel_pt//u --filter 'filter main @ ./tstpltifunc' ./tstpltifunc
thing2
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.016 MB perf.data ]
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
21860.073683659: tr strt 0 [unknown] => 561e212c42be main+0x0
21860.073683659: tr end call 561e212c42c6 main+0x8 => 561e212c4110 fn4@plt+0x0
21860.073683661: tr strt 0 [unknown] => 561e212c42cb main+0xd
21860.073683661: tr end call 561e212c42cb main+0xd => 561e212c40f0 fn1@plt+0x0
21860.073683661: tr strt 0 [unknown] => 561e212c42d0 main+0x12
21860.073683661: tr end call 561e212c42d0 main+0x12 => 561e212c40d0 offset_0x10d0@plt+0x0
21860.073698451: tr strt 0 [unknown] => 561e212c42d5 main+0x17
21860.073698451: tr end call 561e212c42d5 main+0x17 => 561e212c4120 fn2@plt+0x0
21860.073698451: tr strt 0 [unknown] => 561e212c42da main+0x1c
21860.073698451: tr end call 561e212c42da main+0x1c => 561e212c4100 fn3@plt+0x0
21860.073698452: tr strt 0 [unknown] => 561e212c42df main+0x21
21860.073698452: tr end return 561e212c42e5 main+0x27 => 7fb51cc29d90 __libc_start_call_main+0x80
After:
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
21860.073683659: tr strt 0 [unknown] => 561e212c42be main+0x0
21860.073683659: tr end call 561e212c42c6 main+0x8 => 561e212c4110 fn4@plt+0x0
21860.073683661: tr strt 0 [unknown] => 561e212c42cb main+0xd
21860.073683661: tr end call 561e212c42cb main+0xd => 561e212c40f0 fn1@plt+0x0
21860.073683661: tr strt 0 [unknown] => 561e212c42d0 main+0x12
21860.073683661: tr end call 561e212c42d0 main+0x12 => 561e212c40d0 thing_ifunc@plt+0x0
21860.073698451: tr strt 0 [unknown] => 561e212c42d5 main+0x17
21860.073698451: tr end call 561e212c42d5 main+0x17 => 561e212c4120 fn2@plt+0x0
21860.073698451: tr strt 0 [unknown] => 561e212c42da main+0x1c
21860.073698451: tr end call 561e212c42da main+0x1c => 561e212c4100 fn3@plt+0x0
21860.073698452: tr strt 0 [unknown] => 561e212c42df main+0x21
21860.073698452: tr end return 561e212c42e5 main+0x27 => 7fb51cc29d90 __libc_start_call_main+0x80
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 38 +++++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 07cfcf8f40e3..a002fc0bea03 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -381,6 +381,42 @@ static int sort_rel(struct rel_info *ri)
return 0;
}
+/*
+ * For x86_64, the GNU linker is putting IFUNC information in the relocation
+ * addend.
+ */
+static bool addend_may_be_ifunc(GElf_Ehdr *ehdr, struct rel_info *ri)
+{
+ return ehdr->e_machine == EM_X86_64 && ri->is_rela &&
+ GELF_R_TYPE(ri->rela.r_info) == R_X86_64_IRELATIVE;
+}
+
+static bool get_ifunc_name(Elf *elf, struct dso *dso, GElf_Ehdr *ehdr,
+ struct rel_info *ri, char *buf, size_t buf_sz)
+{
+ u64 addr = ri->rela.r_addend;
+ struct symbol *sym;
+ GElf_Phdr phdr;
+
+ if (!addend_may_be_ifunc(ehdr, ri))
+ return false;
+
+ if (elf_read_program_header(elf, addr, &phdr))
+ return false;
+
+ addr -= phdr.p_vaddr - phdr.p_offset;
+
+ sym = dso__find_symbol_nocache(dso, addr);
+
+ /* Expecting the address to be an IFUNC or IFUNC alias */
+ if (!sym || sym->start != addr || (sym->type != STT_GNU_IFUNC && !sym->ifunc_alias))
+ return false;
+
+ snprintf(buf, buf_sz, "%s@plt", sym->name);
+
+ return true;
+}
+
static void exit_rel(struct rel_info *ri)
{
free(ri->sorted);
@@ -560,7 +596,7 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
elf_name = demangled;
if (*elf_name)
snprintf(sympltname, sizeof(sympltname), "%s@plt", elf_name);
- else
+ else if (!get_ifunc_name(elf, dso, &ehdr, &ri, sympltname, sizeof(sympltname)))
snprintf(sympltname, sizeof(sympltname),
"offset_%#" PRIx64 "@plt", plt_offset);
free(demangled);
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 6/9] perf symbols: Allow for .plt without header
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (4 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 5/9] perf symbols: Add support for IFUNC symbols for x86_64 Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 7/9] perf symbols: Allow for static executables with .plt Adrian Hunter
` (3 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
A static executable can have a .plt due to the presence of IFUNCs.
In that case the .plt does not have a header. Check for whether
there is a header by comparing the number of entries to the
number of relocation entries.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index a002fc0bea03..8f7802097c72 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -489,6 +489,7 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
Elf *elf;
int nr = 0, err = -1;
struct rel_info ri = { .is_rela = false };
+ bool lazy_plt;
elf = ss->elf;
ehdr = ss->ehdr;
@@ -523,8 +524,10 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
plt_sym->end = plt_sym->start + shdr_plt.sh_size;
/* Use .plt.sec offset */
plt_offset = plt_sec_shdr.sh_offset;
+ lazy_plt = false;
} else {
- plt_offset = shdr_plt.sh_offset + plt_header_size;
+ plt_offset = shdr_plt.sh_offset;
+ lazy_plt = true;
}
scn_dynsym = ss->dynsym;
@@ -577,6 +580,17 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
ri.is_rela = shdr_rel_plt.sh_type == SHT_RELA;
+ if (lazy_plt) {
+ /*
+ * Assume a .plt with the same number of entries as the number
+ * of relocation entries is not lazy and does not have a header.
+ */
+ if (ri.nr_entries * plt_entry_size == shdr_plt.sh_size)
+ dso__delete_symbol(dso, plt_sym);
+ else
+ plt_offset += plt_header_size;
+ }
+
/*
* x86 doesn't insert IFUNC relocations in .plt order, so sort to get
* back in order.
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 7/9] perf symbols: Allow for static executables with .plt
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (5 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 6/9] perf symbols: Allow for .plt without header Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86 Adrian Hunter
` (2 subsequent siblings)
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
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
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 30 ++++++++++++++++++++----------
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;
--
2.34.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (6 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 7/9] perf symbols: Allow for static executables with .plt Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-02-02 19:41 ` Arnaldo Carvalho de Melo
2023-01-31 13:16 ` [PATCH V2 9/9] perf symbols: Get symbols for .plt.got for x86-64 Adrian Hunter
2023-02-01 6:59 ` [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Namhyung Kim
9 siblings, 1 reply; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
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);
+ 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
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH V2 9/9] perf symbols: Get symbols for .plt.got for x86-64
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (7 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86 Adrian Hunter
@ 2023-01-31 13:16 ` Adrian Hunter
2023-02-01 6:59 ` [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Namhyung Kim
9 siblings, 0 replies; 13+ messages in thread
From: Adrian Hunter @ 2023-01-31 13:16 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
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 | 161 ++++++++++++++++++++++++++++++++++-
1 file changed, 157 insertions(+), 4 deletions(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 254116d40e59..b149cfea73d0 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -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_%#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
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
` (8 preceding siblings ...)
2023-01-31 13:16 ` [PATCH V2 9/9] perf symbols: Get symbols for .plt.got for x86-64 Adrian Hunter
@ 2023-02-01 6:59 ` Namhyung Kim
2023-02-02 0:46 ` Arnaldo Carvalho de Melo
9 siblings, 1 reply; 13+ messages in thread
From: Namhyung Kim @ 2023-02-01 6:59 UTC (permalink / raw)
To: Adrian Hunter
Cc: Arnaldo Carvalho de Melo, Jiri Olsa, Ian Rogers, linux-kernel,
linux-perf-users
Hi Adrian,
On Tue, Jan 31, 2023 at 5:16 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> Hi
>
> This is version 2 of the second of 2 patchsets to improve
> dso__synthesize_plt_symbols().
> This patchset focuses on getting rid of unknown symbols that show up in
> Intel PT traces.
>
> x86 has 2 more plt's, namely .plt.sec and .plt.got, so support is added for
> synthesizing symbols for them. Special handing is needed for IFUNC symbols,
> and it is also possible to have a .plt for static executables, so support is
> added for that.
>
>
> Changes in V2:
>
> perf symbols: Add support for x86 .plt.sec
> Amend commit message and example about -z plt
>
> perf symbols: Get symbols for .plt.got for x86-64
> Fix get_plt_got_name() not to segfault with EM_386
>
>
> Adrian Hunter (9):
> perf symbols: Correct plt entry sizes for x86
> perf symbols: Add support for x86 .plt.sec
> perf symbols: Sort plt relocations for x86
> perf symbols: Record whether a symbol is an alias for an IFUNC symbol
> perf symbols: Add support for IFUNC symbols for x86_64
> perf symbols: Allow for .plt without header
> perf symbols: Allow for static executables with .plt
> perf symbols: Start adding support for .plt.got for x86
> perf symbols: Get symbols for .plt.got for x86-64
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Thanks,
Namhyung
>
> tools/perf/util/symbol-elf.c | 365 ++++++++++++++++++++++++++++++++++++++++---
> tools/perf/util/symbol.c | 4 +
> tools/perf/util/symbol.h | 2 +
> tools/perf/util/symsrc.h | 1 +
> 4 files changed, 350 insertions(+), 22 deletions(-)
>
>
> Regards
> Adrian
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86
2023-02-01 6:59 ` [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Namhyung Kim
@ 2023-02-02 0:46 ` Arnaldo Carvalho de Melo
0 siblings, 0 replies; 13+ messages in thread
From: Arnaldo Carvalho de Melo @ 2023-02-02 0:46 UTC (permalink / raw)
To: Namhyung Kim
Cc: Adrian Hunter, Jiri Olsa, Ian Rogers, linux-kernel, linux-perf-users
Em Tue, Jan 31, 2023 at 10:59:58PM -0800, Namhyung Kim escreveu:
> Hi Adrian,
>
> On Tue, Jan 31, 2023 at 5:16 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
> >
> > Hi
> >
> > This is version 2 of the second of 2 patchsets to improve
> > dso__synthesize_plt_symbols().
> > This patchset focuses on getting rid of unknown symbols that show up in
> > Intel PT traces.
> >
> > x86 has 2 more plt's, namely .plt.sec and .plt.got, so support is added for
> > synthesizing symbols for them. Special handing is needed for IFUNC symbols,
> > and it is also possible to have a .plt for static executables, so support is
> > added for that.
> >
> >
> > Changes in V2:
> >
> > perf symbols: Add support for x86 .plt.sec
> > Amend commit message and example about -z plt
> >
> > perf symbols: Get symbols for .plt.got for x86-64
> > Fix get_plt_got_name() not to segfault with EM_386
> >
> >
> > Adrian Hunter (9):
> > perf symbols: Correct plt entry sizes for x86
> > perf symbols: Add support for x86 .plt.sec
> > perf symbols: Sort plt relocations for x86
> > perf symbols: Record whether a symbol is an alias for an IFUNC symbol
> > perf symbols: Add support for IFUNC symbols for x86_64
> > perf symbols: Allow for .plt without header
> > perf symbols: Allow for static executables with .plt
> > perf symbols: Start adding support for .plt.got for x86
> > perf symbols: Get symbols for .plt.got for x86-64
>
> Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Thanks, applied.
- Arnaldo
> Thanks,
> Namhyung
>
>
> >
> > tools/perf/util/symbol-elf.c | 365 ++++++++++++++++++++++++++++++++++++++++---
> > tools/perf/util/symbol.c | 4 +
> > tools/perf/util/symbol.h | 2 +
> > tools/perf/util/symsrc.h | 1 +
> > 4 files changed, 350 insertions(+), 22 deletions(-)
> >
> >
> > Regards
> > Adrian
--
- Arnaldo
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86
2023-01-31 13:16 ` [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86 Adrian Hunter
@ 2023-02-02 19:41 ` Arnaldo Carvalho de Melo
0 siblings, 0 replies; 13+ messages in thread
From: Arnaldo Carvalho de Melo @ 2023-02-02 19:41 UTC (permalink / raw)
To: Adrian Hunter
Cc: Jiri Olsa, Namhyung Kim, Ian Rogers, linux-kernel, linux-perf-users
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
^ permalink raw reply related [flat|nested] 13+ messages in thread
end of thread, other threads:[~2023-02-02 19:41 UTC | newest]
Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-01-31 13:16 [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 1/9] perf symbols: Correct plt entry sizes " Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 2/9] perf symbols: Add support for x86 .plt.sec Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 3/9] perf symbols: Sort plt relocations for x86 Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 4/9] perf symbols: Record whether a symbol is an alias for an IFUNC symbol Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 5/9] perf symbols: Add support for IFUNC symbols for x86_64 Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 6/9] perf symbols: Allow for .plt without header Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 7/9] perf symbols: Allow for static executables with .plt Adrian Hunter
2023-01-31 13:16 ` [PATCH V2 8/9] perf symbols: Start adding support for .plt.got for x86 Adrian Hunter
2023-02-02 19:41 ` Arnaldo Carvalho de Melo
2023-01-31 13:16 ` [PATCH V2 9/9] perf symbols: Get symbols for .plt.got for x86-64 Adrian Hunter
2023-02-01 6:59 ` [PATCH V2 0/9] perf symbols: Improve dso__synthesize_plt_symbols() for x86 Namhyung Kim
2023-02-02 0:46 ` Arnaldo Carvalho de Melo
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