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SubjectRe: [PATCH] tracing: properly align linker defined symbols
On Sat, Jul 10, 2010 at 07:34:05AM -0400, Steven Rostedt wrote:
> On Sat, 2010-07-10 at 13:18 +0300, Zeev Tarantov wrote:
> > On Sat, Jul 10, 2010 at 09:35, Sam Ravnborg <sam@ravnborg.org> wrote:
>
> > > +/*
> > > + * Align to a 32 byte boundary equal to the
> > > + * alignment gcc 4.5 uses for a struct
> > > + */
> > > +#define STRUCT_ALIGN() . = ALIGN(32)
> > > +
>
> What I'm nervous about is when gcc 4.8 decides to up the alignment to
> 64.
>
> Maybe we should have both patches, just to be safe.

Another approach could be to just stop playing games with alignment
and use the fact that __stop_syscalls_metadata point to next byte
after last entry.

Something like the below untested patch.

But to fix the current regression I prefer the simpler
patch that just fixup the aligment.

Sam


diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 34e3580..50e9606 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -79,15 +79,19 @@ static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
stop = (struct syscall_metadata *)__stop_syscalls_metadata;
kallsyms_lookup(syscall, NULL, NULL, NULL, str);

- for ( ; start < stop; start++) {
+ /*
+ * start may point a few bytes before first entry
+ * stop points at first byte after last entry
+ */
+ for (stop--; stop >= start; stop--) {
/*
* Only compare after the "sys" prefix. Archs that use
* syscall wrappers may have syscalls symbols aliases prefixed
* with "SyS" instead of "sys", leading to an unwanted
* mismatch.
*/
- if (start->name && !strcmp(start->name + 3, str + 3))
- return start;
+ if (stop->name && !strcmp(stop->name + 3, str + 3))
+ return stop;
}
return NULL;
}

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