On Fri, Apr 05, 2019 at 01:25:45AM +0800, Kairui Song wrote: > Currently perf callchain is not working properly with ORC unwinder, > we'll get useless in kernel callchain like this: > > perf 6429 [000] 22.498450: kmem:mm_page_alloc: page=0x176a17 > pfn=1534487 order=0 migratetype=0 gfp_flags=GFP_KERNEL > ffffffffbe23e32e __alloc_pages_nodemask+0x22e > (/lib/modules/5.1.0-rc3+/build/vmlinux) > 7efdf7f7d3e8 __poll+0x18 (/usr/lib64/libc-2.28.so) > 5651468729c1 [unknown] (/usr/bin/perf) > 5651467ee82a main+0x69a (/usr/bin/perf) > 7efdf7eaf413 __libc_start_main+0xf3 (/usr/lib64/libc-2.28.so) > 5541f689495641d7 [unknown] ([unknown]) > > Without CONFIG_FRAME_POINTER, bp is not reserved as frame pointer so > can't get callers frame pointer, instead current frame pointer is > returned when trying to fetch caller registers. The unwinder will error > out early, and end the stacktrace early. > > So instead of let the unwinder start with the dumped register, we start > it right where the unwinding started when the stacktrace is triggered by > trace event directly. And skip until the frame pointer is reached. > > This makes the callchain get the full in kernel stacktrace again: > > perf 6503 [000] 1567.570191: kmem:mm_page_alloc: page=0x16c904 > pfn=1493252 order=0 migratetype=0 gfp_flags=GFP_KERNEL > ffffffffb523e2ae __alloc_pages_nodemask+0x22e > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb52383bd __get_free_pages+0xd > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb52fd28a __pollwait+0x8a > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb521426f perf_poll+0x2f > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb52fe3e2 do_sys_poll+0x252 > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb52ff027 __x64_sys_poll+0x37 > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb500418b do_syscall_64+0x5b > (/lib/modules/5.1.0-rc3+/build/vmlinux) > ffffffffb5a0008c entry_SYSCALL_64_after_hwframe+0x44 > (/lib/modules/5.1.0-rc3+/build/vmlinux) > 7f71e92d03e8 __poll+0x18 (/usr/lib64/libc-2.28.so) > 55a22960d9c1 [unknown] (/usr/bin/perf) > 55a22958982a main+0x69a (/usr/bin/perf) > 7f71e9202413 __libc_start_main+0xf3 (/usr/lib64/libc-2.28.so) > 5541f689495641d7 [unknown] ([unknown]) > > ---- > > Just found with ORC unwinder the perf callchain is unusable, and this > seems fixes it well, any suggestion is welcome, thanks!
Hi Kairui, Without CONFIG_FRAME_POINTER, the BP register has no meaning, so I don't see how this patch could work. Also, perf stack traces seem to work fine for me with ORC. Can you give some details on how to recreate the issue? -- Josh
