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SubjectRe: [PATCH] tracing/x86: fix trace event registration for syscalls without arguments
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On 27/04/2020 17.44, Thomas Gleixner wrote:
> Konstantin Khlebnikov <khlebnikov@yandex-team.ru> writes:
>
>> Syscalls without arguments now has no ABI subs, instead of that macro
>
> What is 'ABI subs'?

typo. ABI stubs

That commmit d2b5de495ee9 ("x86/entry: Refactor SYSCALL_DEFINE0 macros")

replaced usual wrapper

long __x64_syscall()
{
return __do_sys_syscall();
}

with alias

long __x64_syscall() __alias__(__do_sys_syscall);

And now symbol lookup for entry point return "__do_sys_syscall"
rather than "__x64_syscall" and ftrace magic cannot determine
syscall number for entry point and vise versa.

>
>> SYSCALL_DEFINE0() defines __abi_sys_name as aliase to __do_sys_name.
>>
>> As a result in find_syscall_meta() kallsyms_lookup() returns
>> "__do_sys_name" which does not match with declared trace event.
>>
>> Also see commit 1c758a2202a6 ("tracing/x86: Update syscall trace events
>> to handle new prefixed syscall func names")
>>
>> Fixes: d2b5de495ee9 ("x86/entry: Refactor SYSCALL_DEFINE0 macros")
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>> ---
>> arch/x86/include/asm/ftrace.h | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
>> index 85be2f506272..70b96cae5b42 100644
>> --- a/arch/x86/include/asm/ftrace.h
>> +++ b/arch/x86/include/asm/ftrace.h
>> @@ -61,11 +61,12 @@ static inline bool arch_syscall_match_sym_name(const char *sym, const char *name
>> {
>> /*
>> * Compare the symbol name with the system call name. Skip the
>> - * "__x64_sys", "__ia32_sys" or simple "sys" prefix.
>> + * "__x64_sys", "__ia32_sys", "__do_sys" or simple "sys" prefix.
>> */
>> return !strcmp(sym + 3, name + 3) ||
>> (!strncmp(sym, "__x64_", 6) && !strcmp(sym + 9, name + 3)) ||
>> - (!strncmp(sym, "__ia32_", 7) && !strcmp(sym + 10, name + 3));
>> + (!strncmp(sym, "__ia32_", 7) && !strcmp(sym + 10, name + 3)) ||
>> + (!strncmp(sym, "__do_sys", 8) && !strcmp(sym + 8, name + 3));
>> }
>>
>> #ifndef COMPILE_OFFSETS

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