Messages in this thread | | | From | Arnaldo Carvalho de Melo <> | Date | Fri, 3 Apr 2020 10:02:51 -0300 | Subject | Re: [PATCH] perf probe: Add support for DW_OP_call_frame_cfa vars |
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Em Thu, Apr 02, 2020 at 08:25:24PM +0000, Daniel Shaulov escreveu: > 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.
Right, but I tried following your instructions here and got up to this:
<0><76ded>: Abbrev Number: 1 (DW_TAG_compile_unit) <76dee> DW_AT_name : main <76df3> DW_AT_language : 22 (Go) <76df4> DW_AT_stmt_list : 0x27a7d <76df8> DW_AT_low_pc : 0x48cd90 <76e00> DW_AT_ranges : 0x2e0 <76e04> DW_AT_comp_dir : . <76e06> DW_AT_producer : Go cmd/compile go1.13.6 <76e1e> Unknown AT value: 2905: main <1><76e23>: Abbrev Number: 4 (DW_TAG_subprogram) <76e24> DW_AT_name : main.example <76e31> DW_AT_inline : 1 (inlined) <76e32> DW_AT_external : 1 <2><76e33>: Abbrev Number: 17 (DW_TAG_formal_parameter) <76e34> DW_AT_name : param1 <76e3b> DW_AT_variable_parameter: 0 <76e3c> DW_AT_type : <0x37430> <2><76e40>: Abbrev Number: 17 (DW_TAG_formal_parameter) <76e41> DW_AT_name : param2 <76e48> DW_AT_variable_parameter: 0 <76e49> DW_AT_type : <0x37430> <2><76e4d>: Abbrev Number: 0
Which, with or without your patch ends with:
[acme@five daniel.shaulov@gmail.com]$ perf probe -x ./example 'main.example param1 param2' Failed to find 'param1' in this function. Probe point 'main.example' not found. Error: Failed to add events. [acme@five daniel.shaulov@gmail.com]$
[acme@five perf]$ rpm -q golang-bin golang-bin-1.13.6-1.fc31.x86_64 [acme@five perf]$ cat /etc/fedora-release Fedora release 31 (Thirty One) [acme@five perf]$
Has the behaviour changed again in 1.13? Or is this some optimization level that fedora sets that ends up auto-inlining that main.example routine?
[acme@five daniel.shaulov@gmail.com]$ readelf --debug-dump=info ./example | grep main\.example -B10 -A13 <0><76ded>: Abbrev Number: 1 (DW_TAG_compile_unit) <76dee> DW_AT_name : main <76df3> DW_AT_language : 22 (Go) <76df4> DW_AT_stmt_list : 0x27a7d <76df8> DW_AT_low_pc : 0x48cd90 <76e00> DW_AT_ranges : 0x2e0 <76e04> DW_AT_comp_dir : . <76e06> DW_AT_producer : Go cmd/compile go1.13.6 <76e1e> Unknown AT value: 2905: main <1><76e23>: Abbrev Number: 4 (DW_TAG_subprogram) <76e24> DW_AT_name : main.example <76e31> DW_AT_inline : 1 (inlined) <76e32> DW_AT_external : 1 <2><76e33>: Abbrev Number: 17 (DW_TAG_formal_parameter) <76e34> DW_AT_name : param1 <76e3b> DW_AT_variable_parameter: 0 <76e3c> DW_AT_type : <0x37430> <2><76e40>: Abbrev Number: 17 (DW_TAG_formal_parameter) <76e41> DW_AT_name : param2 <76e48> DW_AT_variable_parameter: 0 <76e49> DW_AT_type : <0x37430> <2><76e4d>: Abbrev Number: 0 <1><76e4e>: Abbrev Number: 4 (DW_TAG_subprogram) <76e4f> DW_AT_name : fmt.Println [acme@five daniel.shaulov@gmail.com]$
- Arnaldo
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