Commit 698a0d1a authored by Adrian Hunter's avatar Adrian Hunter Committed by Arnaldo Carvalho de Melo
Browse files

perf symbols: Add symbol for .plt header 



perf expands the _init symbol over .plt because there are no PLT symbols
at that point, but then dso__synthesize_plt_symbols() creates them.

Fix by truncating the previous symbol and inserting a symbol for .plt
header.

Example:

 Before:

   $ perf test --dso `which uname` -v Symbols
    74: Symbols                                                         :
   --- start ---
   test child forked, pid 191028
   Problems creating module maps, continuing anyway...
   Testing /usr/bin/uname
   Overlapping symbols:
    2000-25f0 g _init
    2040-2050 g free@plt
   test child finished with -1
   ---- end ----
   Symbols: FAILED!
   $ perf test --dso `which uname` -vv Symbols 2>/tmp/cmp1.txt

 After:

   $ perf test --dso `which uname` -v Symbols
    74: Symbols                                                         :
   --- start ---
   test child forked, pid 194291
   Testing /usr/bin/uname
   test child finished with 0
   ---- end ----
   Symbols: Ok
   $ perf test --dso `which uname` -vv Symbols 2>/tmp/cmp2.txt
   $ diff /tmp/cmp1.txt /tmp/cmp2.txt
   4,5c4
   < test child forked, pid 191031
   < Problems creating module maps, continuing anyway...
   ---
   > test child forked, pid 194296
   9c8,9
   <  2000-25f0 g _init
   ---
   >  2000-2030 g _init
   >  2030-2040 g .plt
   100,103c100
   < Overlapping symbols:
   <  2000-25f0 g _init
   <  2040-2050 g free@plt
   < test child finished with -1
   ---
   > test child finished with 0
   105c102
   < Symbols: FAILED!
   ---
   > Symbols: Ok
   $

Signed-off-by: default avatarAdrian Hunter <adrian.hunter@intel.com>
Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: default avatarIan Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20230120123456.12449-8-adrian.hunter@intel.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 5fec9b17

tools/perf/util/symbol-elf.c

+21 −5
Original line number Diff line number Diff line
@@ -389,6 +389,27 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) 
	elf = ss->elf;

	ehdr = ss->ehdr;



	if (!elf_section_by_name(elf, &ehdr, &shdr_plt, ".plt", NULL))

		return 0;



	/*

	 * A symbol from a previous section (e.g. .init) can have been expanded

	 * by symbols__fixup_end() to overlap .plt. Truncate it before adding

	 * a symbol for .plt header.

	 */

	f = dso__find_symbol_nocache(dso, shdr_plt.sh_offset);

	if (f && f->start < shdr_plt.sh_offset && f->end > shdr_plt.sh_offset)

		f->end = shdr_plt.sh_offset;



	if (!get_plt_sizes(dso, &ehdr, &shdr_plt, &plt_header_size, &plt_entry_size))

		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)

		goto out_elf_end;

	symbols__insert(&dso->symbols, f);



	scn_dynsym = ss->dynsym;

	shdr_dynsym = ss->dynshdr;

	dynsym_idx = ss->dynsym_idx;
@@ -408,9 +429,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) 
	if (shdr_rel_plt.sh_link != dynsym_idx)

		goto out_elf_end;



	if (elf_section_by_name(elf, &ehdr, &shdr_plt, ".plt", NULL) == NULL)

		goto out_elf_end;



	/*

	 * Fetch the relocation section to find the idxes to the GOT

	 * and the symbols in the .dynsym they refer to.
@@ -436,8 +454,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss) 


	nr_rel_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;

	plt_offset = shdr_plt.sh_offset;

	if (!get_plt_sizes(dso, &ehdr, &shdr_plt, &plt_header_size, &plt_entry_size))

		return 0;

	plt_offset += plt_header_size;



	if (shdr_rel_plt.sh_type == SHT_RELA) {