Re: [PATCH] ARM: ftrace: fix syscall name matching

[Russell King - ARM Linux <linux@armlinux.org.uk>]

On Mon, Nov 14, 2016 at 02:03:45PM +0100, Rabin Vincent wrote:
> From: Rabin Vincent <rabinv@axis.com>
> 
> ARM has a few system calls (most notably mmap) for which the names of
> the functions which are referenced in the syscall table do not match the
> names of the syscall tracepoints.  As a consequence of this, these
> tracepoints are not made available.  Implement
> arch_syscall_match_sym_name to fix this and allow tracing even these
> system calls.
> 
> Signed-off-by: Rabin Vincent <rabinv@axis.com>
> ---
>  arch/arm/include/asm/ftrace.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index bfe2a2f..8467909 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -54,6 +54,27 @@ static inline void *return_address(unsigned int level)
>  
>  #define ftrace_return_address(n) return_address(n)
>  
> +#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
> +
> +static inline bool arch_syscall_match_sym_name(const char *sym,
> +					       const char *name)
> +{
> +	/* Skip sys_ */
> +	sym += 4;
> +	name += 4;

Is this really safe?  What guarantees that we can wind forward four
bytes here?  If it's always safe, it needs a better comment than just
two words.

> +
> +	if (!strcmp(sym, "mmap2"))
> +		sym = "mmap_pgoff";
> +	else if (!strcmp(sym, "statfs64_wrapper"))
> +		sym = "statfs64";
> +	else if (!strcmp(sym, "fstatfs64_wrapper"))
> +		sym = "fstatfs64";
> +	else if (!strcmp(sym, "arm_fadvise64_64"))
> +		sym = "fadvise64_64";
> +
> +	return !strcmp(sym, name);
> +}
> +
>  #endif /* ifndef __ASSEMBLY__ */
>  
>  #endif /* _ASM_ARM_FTRACE */
> -- 
> 2.1.4
> 

-- 
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