svn commit: r334827 - in head/sys: amd64/amd64 arm/arm dev/hwpmc i386/i386 kern mips/atheros mips/cavium powerpc/powerpc sys

[Matthew Macy]

On Fri, Jun 8, 2018 at 07:35 Mark Johnston <markj at freebsd.org> wrote:

> On Fri, Jun 08, 2018 at 04:58:03AM +0000, Matt Macy wrote:
> > Author: mmacy
> > Date: Fri Jun  8 04:58:03 2018
> > New Revision: 334827
> > URL: https://svnweb.freebsd.org/changeset/base/334827
> >
> > Log:
> >   hwpmc: simplify calling convention for hwpmc interrupt handling
> >
> >   pmc_process_interrupt takes 5 arguments when only 3 are needed.
> >   cpu is always available in curcpu and inuserspace can always be
> >   derived from the passed trapframe.
> >
> >   While facially a reasonable cleanup this change was motivated
> >   by the need to workaround a compiler bug.
>
> What is the compiler bug? Do you have disassembly of the subroutines in
> question?
>

We talked about this online. How would that help without engaging in a huge
diversion in to the toolchain? There is nothing wrong with the C code so I
resorted to a voodoo fix to get hwpmc working again. If you're volunteering
mjg or I or you can disassemble the code prior to my change.

>
-M

>
> >
> >   core2_intr(cpu, tf) ->
> >     pmc_process_interrupt(cpu, ring, pmc, tf, inuserspace) ->
> >       pmc_add_sample(cpu, ring, pm, tf, inuserspace)
> >
> >   In the process of optimizing the tail call the tf pointer was getting
> >   clobbered:
> >
> >   (kgdb) up
> >       at /storage/mmacy/devel/freebsd/sys/dev/hwpmc/hwpmc_mod.c:4709
> >   4709
> pmc_save_kernel_callchain(ps->ps_pc,
> >   (kgdb) up
> >   1205                    error = pmc_process_interrupt(cpu, PMC_HR, pm,
> tf,
> >
> >   resulting in a crash in pmc_save_kernel_callchain.
>