Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules
From: James Clark <hidden>
Date: 2021-10-28 08:44:32
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lkml
On 27/10/2021 10:52, Lexi Shao wrote:
On ARM machine, kernel symbols from modules can be resolved to $a instead of printing the actual symbol name. Ignore symbols starting with "$" when building kallsyms rbtree. A sample stacktrace is shown as follows: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 $a+0x78 ([test_module]) c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) On ARM machine, $a/$d symbols are used by the compiler to mark the beginning of code/data part in code section. These symbols are filtered out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but are left on modules. So there are $a symbols in /proc/kallsyms which share the same addresses with the actual module symbols and confuses perf when resolving symbols. After this patch, the module symbol name is printed: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 test_func+0x78 ([test_module]) c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) Signed-off-by: Lexi Shao <redacted>
Reviewed-by: James Clark <redacted>
quoted hunk ↗ jump to hunk
--- tools/perf/util/symbol.c | 4 ++++ 1 file changed, 4 insertions(+)diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index 0fc9a5410739..35116aed74eb 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c@@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, if (!symbol_type__filter(type)) return 0; + /* Ignore local symbols for ARM modules */ + if (name[0] == '$') + return 0; + /* * module symbols are not sorted so we add all * symbols, setting length to 0, and rely on