2021-10-27 21:23:32

by Lexi Shao

Subject: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules

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 <[email protected]>
---
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
--
2.12.3

2021-10-28 08:47:00

by James Clark

Subject: Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules

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 <[email protected]>

Reviewed-by: James Clark <[email protected]>

> ---
> 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
>

2021-11-07 08:58:29

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules

Em Thu, Oct 28, 2021 at 09:44:26AM +0100, James Clark escreveu:
>
>
> 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 <[email protected]>
>
> Reviewed-by: James Clark <[email protected]>

Thanks, applied.

- Arnaldo