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Re: gprof & Linux interaction oddity


Mike Frysinger <vapier@gentoo.org> writes:

> > gprof as such doesn't need to know the timing tick.  The profiling
> > rate is read out of the gmon.out file written by glibc.  glibc appears
> > to compute the rate like this (sysdeps/unix/sysv/linux/prof-freq.c):
> 
> well the issue is the gprof/hertz.c file ... it grabs the hertz value as 
> reported by glibc via sysconf (which it gets from the kernel) and uses that 
> to translate ticks to seconds ... so even though glibc writes out the data 
> correctly, gprof reads it in incorrectly ...

As far as I know this is not the case.  gprof only uses the hertz()
function in hertz.c for files which do not start with GMON_MAGIC
(i.e., "gmon").  The GMON_MAGIC files includes the tick value; older
formats do not.  But glibc generates GMON_MAGIC files, so for them
gprof should not need to get the timing tick.  To confirm what I see
in the sources, I ran strace on gprof, and I did not see it call
sysconf.

If you know otherwise, it would help to have more details.

Ian


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