On Thu, Oct 6, 2022 at 7:00 AM Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> wrote: > > Em Thu, Oct 06, 2022 at 10:43:22AM -0300, Arnaldo Carvalho de Melo escreveu: > > Em Thu, Oct 06, 2022 at 01:54:37PM +0200, Martin Liška escreveu: > > > On 10/5/22 17:43, Arnaldo Carvalho de Melo wrote: > > > > Em Wed, Oct 05, 2022 at 11:37:13AM -0300, Arnaldo Carvalho de Melo escreveu: > > > > So I built and installed from > > > > git://sourceware.org/git/binutils-gdb.git, it got on /usr/local/bin, > > > > taking precedence above /usr/bin/, and didn't get any > > > > DW_TAG_unspecified_type: > > > > > Well, it's more trickier what gcc driver runs as a GAS even though you prefixed > > > /usr/local/bin. > > > > ok > > > > $ echo '' | gcc -c -x c - --verbose 2>&1 | grep 'as\>' > > > /usr/lib64/gcc/x86_64-suse-linux/12/../../../../x86_64-suse-linux/bin/as -v --64 -o -.o /tmp/cclvchQd.s > > > > Anyway, the easiest approach how to use a different gas is using -B gcc option, which > > > would search the location for 'as' binary: > > > > $ pwd > > > /home/marxin/Programming/binutils/objdir/gas > > > $ ./as-new --version > > > GNU assembler (GNU Binutils) 2.39.50.20221004 > > > ... > > > $ ln -s as-new as > > > $ gcc -Wp,-MMD,arch/x86/entry/.entry.o.d -nostdinc -I./arch/x86/include -I./arch/x86/include/generated -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h -D__KERNEL__ -fmacro-prefix-map=./= -D__ASSEMBLY__ -fno-PIE -m64 -c -o arch/x86/entry/entry.o arch/x86/entry/entry.S -g -B/home/marxin/Programming/binutils/objdir/gas > > > > > > (note I'm using make defconfig), and not I can see: > > > > 'make defconfig' doesn't produce DWARF, so I continued using my > > .config, moved the -B to right after 'gcc' in the above command line and > > finally get: > > > > 15e20ce2324a:~/git/linux # readelf -wi ./arch/x86/entry/entry.o > > Contents of the .debug_info section: > > > > Compilation Unit @ offset 0: > > Length: 0x35 (32-bit) > > Version: 5 > > Unit Type: DW_UT_compile (1) > > Abbrev Offset: 0 > > Pointer Size: 8 > > <0><c>: Abbrev Number: 1 (DW_TAG_compile_unit) > > <d> DW_AT_stmt_list : 0 > > <11> DW_AT_low_pc : 0 > > <19> DW_AT_high_pc : 19 > > <1a> DW_AT_name : (indirect string, offset: 0): arch/x86/entry/entry.S > > <1e> DW_AT_comp_dir : (indirect string, offset: 0x17): /root/git/linux > > <22> DW_AT_producer : (indirect string, offset: 0x27): GNU AS 2.39.50 > > <26> DW_AT_language : 32769 (MIPS assembler) > > <1><28>: Abbrev Number: 2 (DW_TAG_subprogram) > > <29> DW_AT_name : (indirect string, offset: 0x36): entry_ibpb > > <2d> DW_AT_external : 1 > > <2d> DW_AT_type : <0x37> > > <2e> DW_AT_low_pc : 0 > > <36> DW_AT_high_pc : 19 > > <1><37>: Abbrev Number: 3 (DW_TAG_unspecified_type) > > <1><38>: Abbrev Number: 0 > > > > 15e20ce2324a:~/git/linux # > > > > Which pahole -J barfs on: > > > > 15e20ce2324a:~/git/linux # pahole -J ./arch/x86/entry/entry.o > > [1] UNKNOWN (anon) Unexpected kind for reference > > 15e20ce2324a:~/git/linux # > > > > But if we ask it to exclude asm CUs (<26> DW_AT_language : 32769 > > (MIPS assembler)) then it ignores it, so this is a workaround. > > > > 15e20ce2324a:~/git/linux # pahole --lang_exclude asm -V -J ./arch/x86/entry/entry.o > > 15e20ce2324a:~/git/linux # > > > > Now I'm looking at how to get the BTF encoder grokking this. > > This is what I came up with, Andrii, Yonghong, wdyt? > Does `const void` make sense? Why not just keeping it as "void"? "const void" might confuse tooling and BTF verifier in kernel, but I haven't checked. Just trying to understand why we need extra "const". > As an additional info clang 14 (haven't tested with other versions) > encodes such ASM Labels as DW_TAG_label and this thus isn't an issue > there. > > - Arnaldo > > commit 15ec614672da043008df31aa6ee85ebc5105d4fd > Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> > Date: Tue Oct 4 18:22:53 2022 -0300 > > btf_encoder: Encode DW_TAG_unspecified_type as BTF_KIND_CONST > > This first appeared for assembler files in the Linux kernel with recent > GNU compilers, we don't have anything in BTF, AFAIK, to properly > represent that, so, for now, lets go with BTF_KIND_CONST. > > Testing it: > > Built binutils from git://sourceware.org/git/binutils-gdb.git, then used > gcc's -B option to point to the directory with the new as, that is built > as as-new, so make a symlink, ending up with: > > 15e20ce2324a:~/git/linux # readelf -wi ./arch/x86/entry/entry.o > Contents of the .debug_info section: > > Compilation Unit @ offset 0: > Length: 0x35 (32-bit) > Version: 5 > Unit Type: DW_UT_compile (1) > Abbrev Offset: 0 > Pointer Size: 8 > <0><c>: Abbrev Number: 1 (DW_TAG_compile_unit) > <d> DW_AT_stmt_list : 0 > <11> DW_AT_low_pc : 0 > <19> DW_AT_high_pc : 19 > <1a> DW_AT_name : (indirect string, offset: 0): arch/x86/entry/entry.S > <1e> DW_AT_comp_dir : (indirect string, offset: 0x17): /root/git/linux > <22> DW_AT_producer : (indirect string, offset: 0x27): GNU AS 2.39.50 > <26> DW_AT_language : 32769 (MIPS assembler) > <1><28>: Abbrev Number: 2 (DW_TAG_subprogram) > <29> DW_AT_name : (indirect string, offset: 0x36): entry_ibpb > <2d> DW_AT_external : 1 > <2d> DW_AT_type : <0x37> > <2e> DW_AT_low_pc : 0 > <36> DW_AT_high_pc : 19 > <1><37>: Abbrev Number: 3 (DW_TAG_unspecified_type) > <1><38>: Abbrev Number: 0 > > So we have that asm label encoded by GNU AS 2.39.50 as a > DW_TAG_subprogram that has as its DW_AT_type the DW_TAG_unspecified_type > 0x37 that we encode as a BTF_KIND_CONST pointing to 0 (void): > > 15e20ce2324a:~/git/linux # pahole -J ./arch/x86/entry/entry.o > 15e20ce2324a:~/git/linux # pahole -JV ./arch/x86/entry/entry.o > btf_encoder__new: './arch/x86/entry/entry.o' doesn't have '.data..percpu' section > Found 0 per-CPU variables! > Found 1 functions! > File ./arch/x86/entry/entry.o: > [1] CONST (anon) type_id=0 > [2] FUNC_PROTO (anon) return=1 args=(void) > [3] FUNC entry_ibpb type_id=2 > 15e20ce2324a:~/git/linux # pfunct -F btf ./arch/x86/entry/entry.o > entry_ibpb > 15e20ce2324a:~/git/linux # pfunct --proto -F btf ./arch/x86/entry/entry.o > const void entry_ibpb(void); > 15e20ce2324a:~/git/linux # > > 15e20ce2324a:~/git/linux # tools/bpf/bpftool/bpftool btf dump file ./arch/x86/entry/entry.o format raw > [1] CONST '(anon)' type_id=0 > [2] FUNC_PROTO '(anon)' ret_type_id=1 vlen=0 > [3] FUNC 'entry_ibpb' type_id=2 linkage=static > 15e20ce2324a:~/git/linux # > > I think this is what can be done to avoid having to skip ASM DWARF when > gets widely used, i.e. binutils gets updated. > > Reported-by: Martin Liška <mliska@xxxxxxx> > Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > Cc: Yonghong Song <yhs@xxxxxx> > Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> > > diff --git a/btf_encoder.c b/btf_encoder.c > index 7ad3f29ef153d8d6..7e50ba711ccc14d6 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -962,6 +962,8 @@ static int btf_encoder__encode_tag(struct btf_encoder *encoder, struct tag *tag, > return btf_encoder__add_enum_type(encoder, tag, conf_load); > case DW_TAG_subroutine_type: > return btf_encoder__add_func_proto(encoder, tag__ftype(tag), type_id_off); > + case DW_TAG_unspecified_type: > + return btf_encoder__add_ref_type(encoder, BTF_KIND_CONST, 0, NULL, false); > default: > fprintf(stderr, "Unsupported DW_TAG_%s(0x%x): type: 0x%x\n", > dwarf_tag_name(tag->tag), tag->tag, ref_type_id);
