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

[Mark Johnston]

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?

>   
>   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.