perf symbols: Sort plt relocations for x86

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 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/20230131131625.6964-4-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2023-01-31 15:16:19 +02:00
parent b2529f829a
commit 78250284b1
1 changed files with 57 additions and 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",