Re: [PATCH 4/6] ftrace syscalls: Allow arch specific syscall symbol matching

[Mike Frysinger]

On Mon, Dec 6, 2010 at 23:29, Ian Munsie wrote:
> From: Ian Munsie <imunsie@xxxxxxxxxxx>
>
> Some architectures have unusual symbol names and the generic code to
> match the symbol name with the function name for the syscall metadata
> will fail. For example, symbols on PPC64 start with a period and the
> generic code will fail to match them.
>
> This patch splits out the match logic into a standalone weak function
> that can be overridden on archs with unusual symbol names.
>
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -527,6 +527,7 @@ extern enum ftrace_dump_mode ftrace_dump_on_oops;
> Â#ifdef CONFIG_FTRACE_SYSCALLS
>
> Âunsigned long arch_syscall_addr(int nr);
> +bool arch_syscall_match_sym_name(const char *sym, const char *name);
>
> Â#endif /* CONFIG_FTRACE_SYSCALLS */
>
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -81,13 +81,7 @@ static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
> Â Â Â Âkallsyms_lookup(syscall, NULL, NULL, NULL, str);
>
> Â Â Â Âfor ( ; start < stop; start++) {
> - Â Â Â Â Â Â Â /*
> - Â Â Â Â Â Â Â Â* Only compare after the "sys" prefix. Archs that use
> - Â Â Â Â Â Â Â Â* syscall wrappers may have syscalls symbols aliases prefixed
> - Â Â Â Â Â Â Â Â* with "SyS" instead of "sys", leading to an unwanted
> - Â Â Â Â Â Â Â Â* mismatch.
> - Â Â Â Â Â Â Â Â*/
> - Â Â Â Â Â Â Â if (start->name && !strcmp(start->name + 3, str + 3))
> + Â Â Â Â Â Â Â if (start->name && arch_syscall_match_sym_name(str, start->name))
> Â Â Â Â Â Â Â Â Â Â Â Âreturn start;
> Â Â Â Â}
> Â Â Â Âreturn NULL;
> @@ -452,6 +446,17 @@ unsigned long __init __weak arch_syscall_addr(int nr)
> Â Â Â Âreturn (unsigned long)sys_call_table[nr];
> Â}
>
> +bool __weak arch_syscall_match_sym_name(const char *sym, const char *name)
> +{
> + Â Â Â /*
> + Â Â Â Â* Only compare after the "sys" prefix. Archs that use
> + Â Â Â Â* syscall wrappers may have syscalls symbols aliases prefixed
> + Â Â Â Â* with "SyS" instead of "sys", leading to an unwanted
> + Â Â Â Â* mismatch.
> + Â Â Â Â*/
> + Â Â Â return (!strcmp(sym + 3, name + 3));
> +}

useless set of parenthesis, and this overhead sucks.  weak +
additional function call just for a strcmp for most people ?  why not
make it into a define in the header:
#ifndef arch_syscall_match_sym_name
#define arch_syscall_match_sym_name(sym, name) !strcmp(sym + 3, name + 3)
#endif
-mike
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