linux-kernel - [PATCH 2/3] perf symbol-elf: Decode dynsym even if symtab exists

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Message-Id: <162532652681.393143.10163733179955267999.stgit@devnote2>
Date:   Sun,  4 Jul 2021 00:35:27 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     linux-perf-users@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Stefan Liebler <stli@...ux.ibm.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] perf symbol-elf: Decode dynsym even if symtab exists

In Fedora34, libc-2.33.so has both .dynsym and .symtab sections and
most of (not all) symbols moved to .dynsym. In this case, perf only
decode the symbols in .symtab, and perf probe can not list up the
functions in the library.

To fix this issue, decode both .symtab and .dynsym sections.

Without this fix,
  -----
  $ ./perf probe -x /usr/lib64/libc-2.33.so -F
  @plt
  @plt
  calloc@plt
  free@plt
  malloc@plt
  memalign@plt
  realloc@plt
  -----

With this fix.

  -----
  $ ./perf probe -x /usr/lib64/libc-2.33.so -F
  @plt
  @plt
  a64l
  abort
  abs
  accept
  accept4
  access
  acct
  addmntent
  -----

Reported-by: Thomas Richter <tmricht@...ux.ibm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/symbol-elf.c |   82 ++++++++++++++++++++++++++++--------------
 1 file changed, 54 insertions(+), 28 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index a73345730ba9..eb10b4e0d888 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1074,8 +1074,9 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 	return 0;
 }
 
-int dso__load_sym(struct dso *dso, struct map *map, struct symsrc *syms_ss,
-		  struct symsrc *runtime_ss, int kmodule)
+static int
+dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
+		       struct symsrc *runtime_ss, int kmodule, int dynsym)
 {
 	struct kmap *kmap = dso->kernel ? map__kmap(map) : NULL;
 	struct maps *kmaps = kmap ? map__kmaps(map) : NULL;
@@ -1098,34 +1099,15 @@ int dso__load_sym(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 	if (kmap && !kmaps)
 		return -1;
 
-	dso->symtab_type = syms_ss->type;
-	dso->is_64_bit = syms_ss->is_64_bit;
-	dso->rel = syms_ss->ehdr.e_type == ET_REL;
-
-	/*
-	 * Modules may already have symbols from kallsyms, but those symbols
-	 * have the wrong values for the dso maps, so remove them.
-	 */
-	if (kmodule && syms_ss->symtab)
-		symbols__delete(&dso->symbols);
-
-	if (!syms_ss->symtab) {
-		/*
-		 * If the vmlinux is stripped, fail so we will fall back
-		 * to using kallsyms. The vmlinux runtime symbols aren't
-		 * of much use.
-		 */
-		if (dso->kernel)
-			goto out_elf_end;
-
-		syms_ss->symtab  = syms_ss->dynsym;
-		syms_ss->symshdr = syms_ss->dynshdr;
-	}
-
 	elf = syms_ss->elf;
 	ehdr = syms_ss->ehdr;
-	sec = syms_ss->symtab;
-	shdr = syms_ss->symshdr;
+	if (dynsym) {
+		sec  = syms_ss->dynsym;
+		shdr = syms_ss->dynshdr;
+	} else {
+		sec =  syms_ss->symtab;
+		shdr = syms_ss->symshdr;
+	}
 
 	if (elf_section_by_name(runtime_ss->elf, &runtime_ss->ehdr, &tshdr,
 				".text", NULL))
@@ -1312,6 +1294,50 @@ int dso__load_sym(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 	return err;
 }
 
+int dso__load_sym(struct dso *dso, struct map *map, struct symsrc *syms_ss,
+		  struct symsrc *runtime_ss, int kmodule)
+{
+	int nr = 0;
+	int err = -1;
+
+	dso->symtab_type = syms_ss->type;
+	dso->is_64_bit = syms_ss->is_64_bit;
+	dso->rel = syms_ss->ehdr.e_type == ET_REL;
+
+	/*
+	 * Modules may already have symbols from kallsyms, but those symbols
+	 * have the wrong values for the dso maps, so remove them.
+	 */
+	if (kmodule && syms_ss->symtab)
+		symbols__delete(&dso->symbols);
+
+	if (!syms_ss->symtab) {
+		/*
+		 * If the vmlinux is stripped, fail so we will fall back
+		 * to using kallsyms. The vmlinux runtime symbols aren't
+		 * of much use.
+		 */
+		if (dso->kernel)
+			return err;
+	} else  {
+		err = dso__load_sym_internal(dso, map, syms_ss, runtime_ss,
+					     kmodule, 0);
+		if (err < 0)
+			return err;
+		nr = err;
+	}
+
+	if (syms_ss->dynsym) {
+		err = dso__load_sym_internal(dso, map, syms_ss, runtime_ss,
+					     kmodule, 1);
+		if (err < 0)
+			return err;
+		err += nr;
+	}
+
+	return err;
+}
+
 static int elf_read_maps(Elf *elf, bool exe, mapfn_t mapfn, void *data)
 {
 	GElf_Phdr phdr;