Re: [DISCUSSION] Three problems behind broken "perf --call-graph dwarf" on AMD: IP and stack dump mismatch, libdw fails on lld's layout, and the unwinder fallback never runs

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Aug 27, 2026 at 02:55:15PM -0700, Namhyung Kim wrote:
> Hello,
> 
> Thanks a lot for your detailed report!  It's good but let me jump into
> the action items directly.
> 
> On Fri, Aug 21, 2026 at 10:49:59PM +0100, Gennady Kupava wrote:
> [SNIP]
> > Suggestions and questions
> > =========================
> > 
> > 1. Kernel: the fix that was applied to the kernel-side call chain -
> >    passing iregs rather than the modified regs - looks like it applies
> >    verbatim to PERF_SAMPLE_REGS_USER and PERF_SAMPLE_STACK_USER.  Should
> >    those be derived from iregs too when the event requests a user stack
> >    dump?  If the precise IP is worth keeping in the sample regardless,
> >    should such samples carry a flag, so that userspace knows the IP and the
> >    stack do not belong together?  Today nothing distinguishes them.
> 
> As Ravi said, you can check the misc field if the IP is from precise
> events.
> 
> And there's PERF_SAMPLE_REGS_INTR which I believe captures registers
> from the interrupt handler.  I don't remember why we have both REGS_USER
> and REGS_INTR but it seems REGS_INTR would work for callchains.

Of course, it won't work when the interrupt was in kernel mode. :(

Thanks,
Namhyung