Arnaldo, Is this patch ready to be merged into Pahole's master branch? Alexei is testing the kernel patches that need this patch. Please let me know if there is anything I can do to help merging. Thank you, Hao On Wed, Aug 26, 2020 at 6:56 PM Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> wrote: > > > > 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.
