On August 26, 2020 3:35:17 PM GMT-03:00, Hao Luo <haoluo@xxxxxxxxxx> wrote: >Arnaldo, > >On Wed, Aug 26, 2020 at 6:12 AM Arnaldo Carvalho de Melo ><acme@xxxxxxxxxx> wrote: >> >> Em Mon, Aug 24, 2020 at 05:45:23PM -0700, Hao Luo escreveu: >> > It is found on gcc 8.2 that global percpu variables generate the >> > following dwarf entry in the cu where the variable is defined[1]. >> > >> > Take the global variable "bpf_prog_active" defined in >> > kernel/bpf/syscall.c as an example. The debug info for syscall.c >> > has two dwarf entries for "bpf_prog_active". >> > >[...] >> >> Interesting, here I get, with binutils' readelf: >> >> [root@quaco perf]# readelf -wi >../build/v5.8-rc5+/kernel/bpf/syscall.o | grep bpf_prog_active >> <f6a1> DW_AT_name : (indirect string, offset: 0xb70d): >bpf_prog_active >> [root@quaco perf]# >> >> Just one, as: >> >> [root@quaco perf]# readelf -wi >../build/v5.8-rc5+/kernel/bpf/syscall.o | grep bpf_prog_active -B1 -A8 >> <1><f6a0>: Abbrev Number: 103 (DW_TAG_variable) >> <f6a1> DW_AT_name : (indirect string, offset: 0xb70d): >bpf_prog_active >> <f6a5> DW_AT_decl_file : 11 >> <f6a6> DW_AT_decl_line : 1008 >> <f6a8> DW_AT_decl_column : 1 >> <f6a9> DW_AT_type : <0xcf> >> <f6ad> DW_AT_external : 1 >> <f6ad> DW_AT_declaration : 1 >> <1><f6ad>: Abbrev Number: 103 (DW_TAG_variable) >> <f6ae> DW_AT_name : (indirect string, offset: 0x3a5d): >bpf_stats_enabled_mutex >> [root@quaco perf]# >> >> I get what you have when I use elfutils' readelf: >> >> [root@quaco perf]# eu-readelf -winfo >../build/v5.8-rc5+/kernel/bpf/syscall.o | grep bpf_prog_active >> name (strp) "bpf_prog_active" >> [ 0] addr .data..percpu+0 <bpf_prog_active> >> [root@quaco perf]# >> >> [root@quaco perf]# eu-readelf -winfo >../build/v5.8-rc5+/kernel/bpf/syscall.o | grep -B1 -A8 >\"bpf_prog_active\" >> [ f6a0] variable abbrev: 103 >> name (strp) "bpf_prog_active" >> decl_file (data1) bpf.h (11) >> decl_line (data2) 1008 >> decl_column (data1) 1 >> type (ref4) [ cf] >> external (flag_present) yes >> declaration (flag_present) yes >> [ f6ad] variable abbrev: 103 >> name (strp) "bpf_stats_enabled_mutex" >> [root@quaco perf]# >> >> And: >> >> [root@quaco perf]# eu-readelf -winfo >../build/v5.8-rc5+/kernel/bpf/syscall.o | grep -B5 \<bpf_prog_active\> >> [ 1bdf5] variable abbrev: 212 >> specification (ref4) [ f6a0] >> decl_file (data1) syscall.c (1) >> decl_line (data1) 43 >> location (exprloc) >> [ 0] addr .data..percpu+0 <bpf_prog_active> >> [root@quaco perf]# >> > >In binutils readelf, there is a extra entry Not here, tomorrow I'll triple check. > > <1><1b24c>: Abbrev Number: 195 (DW_TAG_variable) > <1b24e> DW_AT_specification: <0xf335> > <1b252> DW_AT_decl_file : 1 > <1b253> DW_AT_decl_line : 43 > <1b254> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0 > (DW_OP_addr: 0) > >which points to > > <1><f335>: Abbrev Number: 95 (DW_TAG_variable) > <f336> DW_AT_name : (indirect string, offset: 0xb37a): >bpf_prog_active > >It just doesn't have the string 'bpf_prog_active', annotating entry. >So eu-readelf and binutils readelf have the same results. > >> > Note that second DW_TAG_variable entry contains specification that >> > points to the first entry. >> >> So you are not considering the first when encoding since it is just a >> DW_AT_declaration, considers the second, as it should be, and then >needs >> to go see its DW_AT_specification, right? >> >> Sounds correct, applying, will test further and then push out, >> > >Yes, exactly. The var tags to be considered are those that either have >DW_AT_specification or not have DW_AT_declaration. This makes sure >btf_encoder works correctly on both old and new gcc. > >> Thanks, >> >> - Arnaldo > >Suggested by Yonghong, I tested this change on a larger set of >compilers this time and works correctly. See below. > >Could you also add 'Reported-by: Yonghong Song <yhs@xxxxxx>'? I should >have done that when sending out this patch. The credit goes to >Yonghong. Sure, and I'll add your results with different computers, for the record. Thanks, - Arnaldo > >Thank you, >Hao > > clang 10: > [67] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [20168] VAR 'bpf_prog_active' type_id=67, linkage=global-alloc > > clang 9: > [64] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [19789] VAR 'bpf_prog_active' type_id=64, linkage=global-alloc > > gcc 10.2 > [18] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [20319] VAR 'bpf_prog_active' type_id=18, linkage=global-alloc > > gcc 9.3: > [21] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [21085] VAR 'bpf_prog_active' type_id=21, linkage=global-alloc > > gcc 8 > [21] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [21084] VAR 'bpf_prog_active' type_id=21, linkage=global-alloc > > gcc 6.2 > [22] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [21083] VAR 'bpf_prog_active' type_id=22, linkage=global-alloc > > gcc 4.9 > [17] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [20410] VAR 'bpf_prog_active' type_id=17, linkage=global-alloc -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
