On 17.04.2019 21:47, Arnaldo Carvalho de Melo wrote: > Em Wed, Apr 17, 2019 at 08:45:08PM +0300, Alexey Budankov escreveu: >> Hi Arnaldo, >> >> On 17.04.2019 18:48, Arnaldo Carvalho de Melo wrote: >>> On April 17, 2019 11:40:02 AM GMT-03:00, Jiri Olsa <[email protected]> wrote: >>>> On Wed, Apr 17, 2019 at 11:35:42AM -0300, Arnaldo Carvalho de Melo >>>> wrote: >>>>> Em Wed, Apr 17, 2019 at 09:39:52AM +0200, Jiri Olsa escreveu: >>>>>> On Mon, Apr 15, 2019 at 06:36:13PM +0300, Alexey Budankov wrote: >>>>>>> >>>>>>> When dwarf stacks are collected jointly with user specified >>>> register >>>>>>> set using --user-regs option like below the full register context >>>> is >>>>>>> still captured on a sample: >>>>>>> >>>>>>> $ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP >>>> -- matrix.gcc.g.O3 >>>>>>> >>>>>>> 188143843893585 0x6b48 [0x4f8]: PERF_RECORD_SAMPLE(IP, 0x4002): >>>> 23828/23828: 0x401236 period: 1363819 addr: 0x7ffedbdd51ac >>>>>>> ... FP chain: nr:0 >>>>>>> ... user regs: mask 0xff0fff ABI 64-bit >>>>>>> .... AX 0x53b >>>>>>> .... BX 0x7ffedbdd3cc0 >>>>>>> .... CX 0xffffffff >>>>>>> .... DX 0x33d3a >>>>>>> .... SI 0x7f09b74c38d0 >>>>>>> .... DI 0x0 >>>>>>> .... BP 0x401260 >>>>>>> .... SP 0x7ffedbdd3cc0 >>>>>>> .... IP 0x401236 >>>>>>> .... FLAGS 0x20a >>>>>>> .... CS 0x33 >>>>>>> .... SS 0x2b >>>>>>> .... R8 0x7f09b74c3800 >>>>>>> .... R9 0x7f09b74c2da0 >>>>>>> .... R10 0xfffffffffffff3ce >>>>>>> .... R11 0x246 >>>>>>> .... R12 0x401070 >>>>>>> .... R13 0x7ffedbdd5db0 >>>>>>> .... R14 0x0 >>>>>>> .... R15 0x0 >>>>>>> ... ustack: size 1024, offset 0xe0 >>>>>>> . data_src: 0x5080021 >>>>>>> ... thread: stack_test2.g.O:23828 >>>>>>> ...... dso: /root/abudanko/stacks/stack_test2.g.O3 >>>>>>> >>>>>>> After applying the change suggested in the patch the sample data >>>> contain >>>>>>> only user specified register values: >>>>>>> >>>>>>> $ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP >>>> -- matrix.gcc.g.03 >>>>>>> >>>>>>> 188368474305373 0x5e40 [0x470]: PERF_RECORD_SAMPLE(IP, 0x4002): >>>> 23839/23839: 0x401236 period: 1260507 addr: 0x7ffd3d85e96c >>>>>>> ... FP chain: nr:0 >>>>>>> ... user regs: mask 0x1c0 ABI 64-bit >>>>>>> .... BP 0x401260 >>>>>>> .... SP 0x7ffd3d85cc20 >>>>>>> .... IP 0x401236 >>>>>>> ... ustack: size 1024, offset 0x58 >>>>>>> . data_src: 0x5080021 >>>>>>> ... thread: stack_test2.g.O:23839 >>>>>>> ...... dso: /root/abudanko/stacks/stack_test2.g.O3 >>>>>>> >>>>>>> Signed-off-by: Alexey Budankov <[email protected]> >>>>>> >>>>>> Acked-by: Jiri Olsa <[email protected]> >>>>> >>>>> So, there are registers that are needed to do the DWARF unwinding, >>>>> right? But at the same time, if the user says only some are needed, >>>> he >>>>> better know what they're doing and ask for at least the registers >>>> needed >>>>> for the unwinding process to be successfull, right? >>>> >>>> yep, that's how understand that >>> >>> So we need to document that, stating that specifying a set of registers >>> together with requesting DWARF callchains may break things. >> >> Do you mean break callchains if omitting IP,SP,BP? >> For example like this: >> $ perf record -g --call-graph dwarf,1024 --user-regs=AX,BX,CX -- >> matrix.gcc.g.O3 > > Right, i.e. if you don't use --user-regs, then a set of registers will > be asked for by --call-graph dwarf, right? If you use both and specify a
Right. Full register set is collected. > subset that doesn't have some of the asked for --call-graph dwarf, what > happens? It reports corrupted trace: ./perf record -g --call-graph dwarf,1024 --user-regs=IP -- ./stack_test2.2048.g.O3 in foo() ... in bar() ... done [ perf record: Woken up 254 times to write data ] [ perf record: Captured and wrote 63.341 MB perf.data (59286 samples) ] [root@nntvtune39 stacks]# ./perf report -D > log.txt unwind: can't read reg 7 0x835c0 [0x8]: failed to process type: 68 Error: failed to process sample ./perf record -g --call-graph dwarf,1024 --user-regs=SP -- ./stack_test2.2048.g.O3 in foo() ... in bar() ... done [ perf record: Woken up 256 times to write data ] [ perf record: Captured and wrote 63.863 MB perf.data (59773 samples) ] [root@nntvtune39 stacks]# ./perf report -D > log.txt 0x83180 [0x8]: failed to process type: 68 Error: failed to process sample ./perf record -g --call-graph dwarf,1024 --user-regs=IP,SP -- ./stack_test2.2048.g.O3 in foo() ... in bar() ... done [ perf record: Woken up 258 times to write data ] [ perf record: Captured and wrote 64.301 MB perf.data (59757 samples) ] [root@nntvtune39 stacks]# ./perf report -D > log.txt unwind: can't read reg 6 ./perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP -- ./stack_test2.2048.g.O3 in foo() ... in bar() ... done [ perf record: Woken up 259 times to write data ] [ perf record: Captured and wrote 64.737 MB perf.data (59739 samples) ] [root@nntvtune39 stacks]# ./perf report -D > log.txt It looks like some dwarf set IP,SP,BP has to be collected anyways and the set has to be consolidated with the registers specified using --user-regs option: -g call-graph dwarf,K all_regs -g call-graph dwarf,K --user-regs=user_regs dwarf_regs | user_regs --user-regs=user_regs user_regs ~Alexey > > - Arnaldo >
