Messages in this thread |  | | Date | Thu, 2 Apr 2020 20:25:24 +0000 | From | Daniel Shaulov <> | Subject | Re: [PATCH] perf probe: Add support for DW_OP_call_frame_cfa vars |
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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.
Daniel.
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