[V2,3/9] perf symbols: Sort plt relocations for x86
Commit Message
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(-)
@@ -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",