Messages in this thread | | | Date | Fri, 3 Apr 2020 14:39:56 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] perf probe: Add support for DW_OP_call_frame_cfa vars |
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Hi Daniel,
On Thu, 2 Apr 2020 20:25:24 +0000 Daniel Shaulov <daniel.shaulov@gmail.com> wrote:
> On Thu, Apr 02, 2020 at 03:49:43PM -0300, Arnaldo Carvalho de Melo wrote: > > Daniel, next time please consider providing precise steps to show what > > wasn't working and then how the patch solves the problem, i.e. get some > > go program, show the command lines used to build, probe, etc. > > > > - Arnaldo > > Sure thing: > > ---- contents of example.go ---- > package main > > import "fmt" > > func example(param1 int, param2 int) { > fmt.Println(param1, param2) > } > > func main() { > example(111, 222) > } > ---- end contents of example.go ---- > > Build with: > $ go build example.go > > Note that the output file is named after the directory. > > Then try to probe it with: > $ perf probe -x ./example 'main.example param1 param2' > > The result is: > > Target program is compiled without optimization. Skipping prologue. > > Probe on address 0x4820f0 to force probing at the function entry. > > > > Sorry, we don't support this variable location yet. > > Error: Failed to add events. > > With my changes the event is added successfuly. > The reason for the change can be observed in the output of: > $ readelf --debug-dump=info ./example > > Where we have the following for the main.example function (with go >= 1.10): > <1><63dd2>: Abbrev Number: 2 (DW_TAG_subprogram) > <63dd3> DW_AT_name : main.example > <63de0> DW_AT_low_pc : 0x4820f0 > <63de8> DW_AT_high_pc : 0x4821c2 > <63df0> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) > <63df2> DW_AT_decl_file : 0x1 > <63df6> DW_AT_external : 1 > <2><63df7>: Abbrev Number: 14 (DW_TAG_formal_parameter) > <63df8> DW_AT_name : param1 > <63dff> DW_AT_variable_parameter: 0 > <63e00> DW_AT_decl_line : 5 > <63e01> DW_AT_type : <0x220f> > <63e05> DW_AT_location : 1 byte block: 9c (DW_OP_call_frame_cfa) > <2><63e07>: Abbrev Number: 14 (DW_TAG_formal_parameter) > <63e08> DW_AT_name : param2 > <63e0f> DW_AT_variable_parameter: 0 > <63e10> DW_AT_decl_line : 5 > <63e11> DW_AT_type : <0x220f> > <63e15> DW_AT_location : 2 byte block: 91 8 (DW_OP_fbreg: 8) > <2><63e18>: Abbrev Number: 0 > > The go compiler (after 1.10) uses DW_OP_call_frame_cfa for the first parameter and DW_OP_fbreg for the rest. > On go versions lower than 1.10, it used DW_OP_call_frame_cfa for all parameters. > Here is example output of the readelf on main.example, compiled with go1.9.7: > <1><2634d>: Abbrev Number: 2 (DW_TAG_subprogram) > <2634e> DW_AT_name : main.example > <2635b> DW_AT_low_pc : 0x487db0 > <26363> DW_AT_high_pc : 0x487e99 > <2636b> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) > <2636d> DW_AT_external : 1 > <2><2636e>: Abbrev Number: 5 (DW_TAG_formal_parameter) > <2636f> DW_AT_name : param1 > <26376> DW_AT_location : 1 byte block: 9c (DW_OP_call_frame_cfa) > <26378> DW_AT_type : <0x27f1c> > <2><2637c>: Abbrev Number: 5 (DW_TAG_formal_parameter) > <2637d> DW_AT_name : param2 > <26384> DW_AT_location : 4 byte block: 9c 11 8 22 (DW_OP_call_frame_cfa; DW_OP_consts: 8; DW_OP_plus) > <26389> DW_AT_type : <0x27f1c> > <2><2638d>: Abbrev Number: 0 > > Hope this makes things easier to understand.
Thanks for the explanation. That is a useful info to understand what go compiler does on dwarf. OK, so that is same as "DW_OP_fbreg: 0".
Thank you,
> > Daniel. >
-- Masami Hiramatsu <mhiramat@kernel.org>
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