linux-kernel - Re: [PATCH] powerpc/ftrace: fix syscall tracing on PPC64_ELF_ABI

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Date:   Mon, 5 Dec 2022 13:19:34 -0500
From:   Michael Jeanson <mjeanson@...icios.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     stable@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michal Suchanek <msuchanek@...e.de>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] powerpc/ftrace: fix syscall tracing on PPC64_ELF_ABI_V1

On 2022-12-05 00:34, Michael Ellerman wrote:
> Michael Jeanson <mjeanson@...icios.com> writes:
>> In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on
>> PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table
>> changing from their dot prefixed variant to the non-prefixed ones.
>>
>> Since ftrace prefixes a dot to the syscall names when matching them to
>> build its syscall event list, this resulted in no syscall events being
>> available.
>>
>> Remove the PPC64_ELF_ABI_V1 specific version of
>> arch_syscall_match_sym_name to have the same behavior across all powerpc
>> variants.
> 
> This doesn't seem to work for me.
> 
> Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
> 
> Did we break it in some other way recently?
> 
> cheers

I've just tried this change on top of v6.1-rc8 in qemu with a base config of 
'corenet32_smp_defconfig' and these options on top:

CONFIG_FTRACE=y
CONFIG_FTRACE_SYSCALLS=y

And I can trace syscalls with ftrace.

What kernel tree and config are you using?

Thanks for looking into this.

> 
> 
>> Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C")
>> Cc: stable@...r.kernel.org # v5.7+
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Cc: Nicholas Piggin <npiggin@...il.com>
>> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
>> Cc: Michal Suchanek <msuchanek@...e.de>
>> Cc: linuxppc-dev@...ts.ozlabs.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Michael Jeanson <mjeanson@...icios.com>
>> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> ---
>>   arch/powerpc/include/asm/ftrace.h | 12 ------------
>>   1 file changed, 12 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
>> index 3cee7115441b..e3d1f377bc5b 100644
>> --- a/arch/powerpc/include/asm/ftrace.h
>> +++ b/arch/powerpc/include/asm/ftrace.h
>> @@ -64,17 +64,6 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
>>    * those.
>>    */
>>   #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
>> -#ifdef CONFIG_PPC64_ELF_ABI_V1
>> -static inline bool arch_syscall_match_sym_name(const char *sym, const char *name)
>> -{
>> -	/* We need to skip past the initial dot, and the __se_sys alias */
>> -	return !strcmp(sym + 1, name) ||
>> -		(!strncmp(sym, ".__se_sys", 9) && !strcmp(sym + 6, name)) ||
>> -		(!strncmp(sym, ".ppc_", 5) && !strcmp(sym + 5, name + 4)) ||
>> -		(!strncmp(sym, ".ppc32_", 7) && !strcmp(sym + 7, name + 4)) ||
>> -		(!strncmp(sym, ".ppc64_", 7) && !strcmp(sym + 7, name + 4));
>> -}
>> -#else
>>   static inline bool arch_syscall_match_sym_name(const char *sym, const char *name)
>>   {
>>   	return !strcmp(sym, name) ||
>> @@ -83,7 +72,6 @@ static inline bool arch_syscall_match_sym_name(const char *sym, const char *name
>>   		(!strncmp(sym, "ppc32_", 6) && !strcmp(sym + 6, name + 4)) ||
>>   		(!strncmp(sym, "ppc64_", 6) && !strcmp(sym + 6, name + 4));
>>   }
>> -#endif /* CONFIG_PPC64_ELF_ABI_V1 */
>>   #endif /* CONFIG_FTRACE_SYSCALLS */
>>   
>>   #if defined(CONFIG_PPC64) && defined(CONFIG_FUNCTION_TRACER)
>> -- 
>> 2.34.1