Messages in this thread |  | | Date | Mon, 4 May 2026 16:48:36 -0700 | | From | Namhyung Kim <> | | Subject | Re: [PATCH] perf callchain: Handle multiple address spaces |
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On Mon, May 04, 2026 at 11:56:15AM +0200, Thomas Richter wrote: > On 4/30/26 04:57, Namhyung Kim wrote: > > On Wed, Apr 29, 2026 at 09:14:38AM +0200, Thomas Richter wrote: > >> On 4/21/26 18:30, Namhyung Kim wrote: > >>> Hello, > >>> > >>> On Tue, Apr 14, 2026 at 02:42:41PM +0200, Thomas Richter wrote: > >>>> perf test 'perf inject to convert DWARF callchains to regular ones' > >>>> fails on s390. It was introduced with > >>>> commit 92ea788d2af4 ("perf inject: Add --convert-callchain option") > >>>> > >>>> The failure comes the difference in output. Without the inject script to > >>>> convert DWARF the callchains is: > >>>> # ./perf record -F 999 --call-graph dwarf -- perf test -w noploop > >>>> # ./perf report -i perf.data --stdio --no-children -q \ > >>>> --percent-limit=1 > /tmp/111 > >>>> # cat /tmp/111 > >>>> 99.30% perf-noploop perf [.] noploop > >>>> | > >>>> ---noploop > >>>> run_workload (inlined) > >>>> cmd_test > >>>> run_builtin (inlined) > >>>> handle_internal_command > >>>> run_argv (inlined) > >>>> main > >>>> __libc_start_call_main > >>>> __libc_start_main_impl (inlined) > >>>> _start > >>>> # > >>>> > >>>> With the inject script step the output is: > >>>> # ./perf inject -i perf.data --convert-callchain -o /tmp/perf-inject-1.out > >>>> # ./perf report -i /tmp/perf-inject-1.out --stdio --no-children -q \ > >>>> --percent-limit=1 > /tmp/222 > >>>> # cat /tmp/222 > >>>> 99.40% perf-noploop perf [.] noploop > >>>> | > >>>> ---noploop > >>>> run_workload (inlined) > >>>> cmd_test > >>>> run_builtin (inlined) > >>>> handle_internal_command > >>>> run_argv (inlined) > >>>> main > >>>> _start > >>>> # diff /tmp/111 /tmp/222 > >>>> 1c1 > >>>> < 99.30% perf-noploop perf [.] noploop > >>>> --- > >>>> > 99.40% perf-noploop perf [.] noploop > >>>> 10,11d9 > >>>> < __libc_start_call_main > >>>> < __libc_start_main_impl (inlined) > >>>> # > >>>> > >>>> The difference are the symbols __libc_start_call_main and > >>>> __libc_start_main_impl. > >>>> > >>>> On x86_64, kernel and user space share a single virtual address space, > >>>> with the kernel mapped to the upper end of memory. The instruction > >>>> pointer value alone is sufficient to distinguish between user space > >>>> and kernel space addresses. This is not true for s390, which uses > >>>> separate address spaces for user and kernel. The same virtual address > >>>> can be valid in both address spaces, so the instruction pointer value > >>>> alone cannot determine whether an address belongs to the kernel or > >>>> user space. Instead, perf must rely on the cpumode metadata derived > >>>> from the processor status word (PSW) at sample time. > >>>> > >>>> In function perf_event__convert_sample_callchain() the first part > >>>> copies a kernel callchain and context entries, if any. > >>>> It then appends additional entries ignoring the address space > >>>> architecture. Taking that into account, the symbols at addresses > >>>> > >>>> 0x3ff970348cb __libc_start_call_main > >>>> 0x3ff970349c5 __libc_start_main_impl > >>>> > >>>> (located after the kernel address space on s390) are now included. > >>>> > >>>> Output before: > >>>> # ./perf test 83 > >>>> 83: perf inject to convert DWARF callchains to regular ones : FAILED! > >>>> > >>>> Output after: > >>>> # ./perf test 83 > >>>> 83: perf inject to convert DWARF callchains to regular ones : Ok > >>>> > >>>> Question to Namhyung: > >>>> In function perf_event__convert_sample_callchain() just before the > >>>> for() loop this patch modifies, the kernel callchain is copied, > >>>> see this comment and the next 5 lines: > >>>> /* copy kernel callchain and context entries */ > >>>> Then why is machine__kernel_ip() needed in the for() loop, when > >>>> the kernel entries have been copied just before the loop? > >>> > >>> IIRC I wanted to make sure to have PERF_CONTEXT_* part in the raw > >>> callchains. > >>> > >>>> > >>>> Note: This patch was tested on x86_64 virtual machine and succeeded. > >>>> > >>>> Fixes: 92ea788d2af4 ("perf inject: Add --convert-callchain option") > >>>> Cc: Namhyung Kim <namhyung@kernel.org> > >>>> > >>>> Signed-off-by: Thomas Richter <tmricht@linux.ibm.com> > >>> > >>> Acked-by: Namhyung Kim <namhyung@kernel.org> > >>> > >>> Thanks, > >>> Namhyung > >>> > >> > >> Hi Namhyung, > >> > >> is there something which needs to be done on my side to get this patch picked? > >> It still fails on s390. > >> > >> Please adviseon how to proceed. > > > > Arnaldo will take care of 7.2 development cycle. > > > > Today we are at v7.1-rc2. Does this mean the fix won't make it into v7.1 at all > and we have to wait roughly 2 month?
Just out of curiousity, do you plan to use v7.1 for this feature specifically or just for test failures? Probably better to use v7.2 series (i.e. perf-tools-next) instead?
Anyway, I can merge this to v7.1 if you really want as it's from v7.0 which may be close enough for urgent care. :) But it seems there would be conflicts with Ian's e_machine patchset.
Thanks, Namhyung
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