Messages in this thread | | | From | Lexi Shao <> | Subject | Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules | Date | Wed, 27 Oct 2021 20:31:08 +0800 |
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On 27/10/2021 18:24, James Clark wrote: >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 $a symbols in /proc/kallsyms which >> share the same addresses with the actual module symbols and confuses perf >> when resolving symbols. > >Hi Lexi, > >Is it worth using or re-implementing the entire is_ignored_symbol() function >from scripts/kallsyms.c? It seems like this change only fixes one occurrence, >but is_ignored_symbol() has a big list of other cases. > >Unless those cases are different? > >Thanks >James
Hi James,
I don't think it's necessary to cover all the cases listed in is_ignored_symbol(). As long as the symbols are unique and not overlapping with each other, they should't cause problems in resolving symbols. So most of the cases in is_ignored_symbol() should be irrelevant.
Lexi
> >> >> After this patch, the module symbol name is printed: >> >> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >> bf4a66d8 test_func+0x78 ([test_module]) >> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >> >> Signed-off-by: Lexi Shao <shaolexi@huawei.com> >> --- >> tools/perf/util/symbol.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c >> index 0fc9a5410739..35116aed74eb 100644 >> --- a/tools/perf/util/symbol.c >> +++ b/tools/perf/util/symbol.c >> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, >> if (!symbol_type__filter(type)) >> return 0; >> >> + /* Ignore local symbols for ARM modules */ >> + if (name[0] == '$') >> + return 0; >> + >> /* >> * module symbols are not sorted so we add all >> * symbols, setting length to 0, and rely on >> >
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