On Tue, 2011-08-30 at 20:20 +0400, Dmitry V. Levin wrote:
> On Wed, Aug 24, 2011 at 11:41:10PM +0000, Denys Vlasenko wrote:
> > commit 102ec4935440ff52a7fa3566154a84cc2473f16a
> > Author: Denys Vlasenko <[email protected]>
> > Date: Thu Aug 25 01:27:59 2011 +0200
> >
> > Optimize tabto()
> >
> > tabto is used in many lines of strace output.
> > On glibc, tprintf("%*s", col - curcol, "") is noticeably slow
> > compared to tprintf(" "). Use the latter.
> > Observed ~15% reduction of time spent in userspace.
> >
> > * defs.h: Drop extern declaration of acolumn. Make tabto()
> > take no parameters.
> > * process.c (sys_exit): Call tabto() with no parameters.
> > * syscall.c (trace_syscall_exiting): Call tabto() with no parameters.
> > * strace.c: Make acolumn static, add static char *acolumn_spaces.
> > (main): Allocate acolumn_spaces as a string of spaces.
> > (printleader): Call tabto() with no parameters.
> > (tabto): Use simpler method to print lots of spaces.
> [...]
> > void
> > -tabto(int col)
> > +tabto(void)
> > {
> > - if (curcol < col)
> > - tprintf("%*s", col - curcol, "");
> > + if (curcol < acolumn)
> > + tprintf(acolumn_spaces + curcol);
> > }
>
> The new statement yields a warning:
>
> strace.c: In function 'tabto':
> strace.c:2701:3: warning: format not a string literal and no format arguments
Pity, my toolchain doesn't emit that... I can't detect these warnings.
> Maybe we could use
> tprintf("%s", acolumn_spaces + curcol);
> instead without performance degradation?
There will be some performance degradation.
Is there a way to suppress this warning on a case-by-case basis?
--
vda
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