Re: [PATCH] tracing/x86: fix trace event registration for syscalls without arguments

[Konstantin Khlebnikov]

On 27/04/2020 17.44, Thomas Gleixner wrote:
> Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > ---
> >   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