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 ~Alexey > > - Arnaldo > > > > >
