perf: Ignore stripped vmlinux and fallback to kallsyms

PATCH In review Anton Blanchard 3 participants 3 messages Sep 8, 2014 – Sep 19, 2014 perf events

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Anton Blanchard

author

2014-09-08 22:59 UTC #0 lore raw

PATCH 1/1 perf: Ignore stripped vmlinux and fallback to kallsyms

If a vmlinux is stripped, perf will use it and ignore kallsyms. We end up with useless profiles where everything maps to a few runtime symbols:

    63.39%       swapper  [kernel.kallsyms]   [k] hcall_real_table
     4.90%      beam.smp  [kernel.kallsyms]   [k] hcall_real_table
     4.44%      beam.smp  [kernel.kallsyms]   [k] __sched_text_start
     3.72%      beam.smp  [kernel.kallsyms]   [k] __run_at_kexec

Detect this case and fallback to using kallsyms. This fixes the issue:

    62.81%       swapper  [kernel.kallsyms]   [k] snooze_loop
     4.44%      beam.smp  [kernel.kallsyms]   [k] __schedule
     0.91%      beam.smp  [kernel.kallsyms]   [k] _switch
     0.73%      beam.smp  [kernel.kallsyms]   [k] put_prev_entity

Signed-off-by Anton Blanchard <[email protected]>

---

tools/perf/util/symbol-elf.c +8 -0

Index: b/tools/perf/util/symbol-elf.c
===================================================================
@@ -712,6 +712,14 @@ int dso__load_sym(struct dso *dso, struc
 		symbols__delete(&dso->symbols[map->type]);
 
 	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;
 	}

Namhyung Kim

maintainer Acked-by on v1 1/1

2014-09-12 06:33 UTC #1 lore raw

Hi Anton,

Quoted 9 lines · Anton Blanchard

If a vmlinux is stripped, perf will use it and ignore kallsyms. We end up with useless profiles where everything maps to a few runtime symbols:
    63.39%       swapper  [kernel.kallsyms]   [k] hcall_real_table
     4.90%      beam.smp  [kernel.kallsyms]   [k] hcall_real_table
     4.44%      beam.smp  [kernel.kallsyms]   [k] __sched_text_start
     3.72%      beam.smp  [kernel.kallsyms]   [k] __run_at_kexec

Quoted 8 lines

Detect this case and fallback to using kallsyms. This fixes the issue:
    62.81%       swapper  [kernel.kallsyms]   [k] snooze_loop
     4.44%      beam.smp  [kernel.kallsyms]   [k] __schedule
     0.91%      beam.smp  [kernel.kallsyms]   [k] _switch
     0.73%      beam.smp  [kernel.kallsyms]   [k] put_prev_entity
Signed-off-by Anton Blanchard <[email protected]>

Acked-by Namhyung Kim <[email protected]>

Thanks,
Namhyung

Quoted 21 lines

---

Index: b/tools/perf/util/symbol-elf.c
===================================================================

tools/perf/util/symbol-elf.c +8 -0

@@ -712,6 +712,14 @@ int dso__load_sym(struct dso *dso, struc
 		symbols__delete(&dso->symbols[map->type]);
 
 	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;
 	}

tip-bot for Anton Blanchard

merge bot

2014-09-19 05:22 UTC #2 lore raw

[tip:perf/core] perf symbols: Ignore stripped vmlinux and fallback to kallsyms

In reply to Anton Blanchard

perf symbols: Ignore stripped vmlinux and fallback to kallsyms

Commit-ID:  d0b0d0406fe6743e734e1ba780155f8db5f713e6
Gitweb:     http://git.kernel.org/tip/d0b0d0406fe6743e734e1ba780155f8db5f713e6
Author:     Anton Blanchard <[email protected]>
AuthorDate: Tue, 9 Sep 2014 08:59:29 +1000
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Wed, 17 Sep 2014 17:08:10 -0300

perf symbols: Ignore stripped vmlinux and fallback to kallsyms

If a vmlinux is stripped, perf will use it and ignore kallsyms. We end up with useless profiles where everything maps to a few runtime symbols:

    63.39%       swapper  [kernel.kallsyms]   [k] hcall_real_table
     4.90%      beam.smp  [kernel.kallsyms]   [k] hcall_real_table
     4.44%      beam.smp  [kernel.kallsyms]   [k] __sched_text_start
     3.72%      beam.smp  [kernel.kallsyms]   [k] __run_at_kexec

Detect this case and fallback to using kallsyms. This fixes the issue:

    62.81%       swapper  [kernel.kallsyms]   [k] snooze_loop
     4.44%      beam.smp  [kernel.kallsyms]   [k] __schedule
     0.91%      beam.smp  [kernel.kallsyms]   [k] _switch
     0.73%      beam.smp  [kernel.kallsyms]   [k] put_prev_entity

Signed-off-by Anton Blanchard <[email protected]>

Acked-by Namhyung Kim <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc Paul Mackerras <[email protected]>

Cc Peter Zijlstra <[email protected]>

Link http://lkml.kernel.org/r/20140909085929.4a5a81f0@kryten open here

Signed-off-by Arnaldo Carvalho de Melo <[email protected]>

---
 tools/perf/util/symbol-elf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

tools/perf/util/symbol-elf.c +8 -0

index 9c9b27f..2a92e10 100644
@@ -717,6 +717,14 @@ int dso__load_sym(struct dso *dso, struct map *map,
 		symbols__delete(&dso->symbols[map->type]);
 
 	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;
 	}