Em Mon, Oct 10, 2022 at 05:08:26PM -0300, Arnaldo Carvalho de Melo escreveu: > Em Mon, Oct 10, 2022 at 09:06:46AM -0300, Arnaldo Carvalho de Melo escreveu: > > Em Fri, Oct 07, 2022 at 05:25:21PM -0700, Yonghong Song escreveu: > > > For function entry_ibpb, actually the kernel has a prorotype, > > > include/asm/nospec-branch.h:extern void entry_ibpb(void); > > > But unfortunately since the function is defined in asm code. > > > The actual type information is not encoded in dwarf so pahole > > > does not have enough info from vmlinux dwarf to get func > > > types. The compiler does not generate func types based on > > > declarations. > > Right > > > > This may prevent people from tracing functions defined in > > > asm code but this should be extremely rare. > > > So I agree that BTF type id 0 is probably the best choice. > > > > Thanks for your comments, that is the way I'll do it. > > Done, some prep patches then the patch below. > > If possible, please ack :-) Its all now on my 'next' branch at: git://git.kernel.org/pub/scm/devel/pahole/pahole.git https://github.com/acmel/dwarves.git https://git.kernel.org/pub/scm/devel/pahole/pahole.git/log/?h=next > - Arnaldo > > commit 3abc72d9d56ec0cbfffc1794d2bf5d527d1e88ba > Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> > Date: Mon Oct 10 11:20:07 2022 -0300 > > btf_encoder: Encode DW_TAG_unspecified_type returning routines as void > > Since we don´t have how to encode this info in BTF, and from what we > saw, at least in this case: > > 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 convert 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: 'entry.o' doesn't have '.data..percpu' section > Found 0 per-CPU variables! > Found 1 functions! > File entry.o: > [1] FUNC_PROTO (anon) return=0 args=(void) > [2] FUNC entry_ibpb type_id=1 > 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 > 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] FUNC_PROTO '(anon)' ret_type_id=0 vlen=0 > [2] FUNC 'entry_ibpb' type_id=1 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. > > Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>, > Cc: Martin Liška <mliska@xxxxxxx> > Cc: Yonghong Song <yhs@xxxxxxxx> > Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> > > diff --git a/btf_encoder.c b/btf_encoder.c > index fb2ca77e2e9bf144..a5fa04a84ee246ee 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -593,6 +593,19 @@ static int32_t btf_encoder__add_func_param(struct btf_encoder *encoder, const ch > } > } > > +static int32_t btf_encoder__tag_type(struct btf_encoder *encoder, uint32_t type_id_off, uint32_t tag_type) > +{ > + if (tag_type == 0) > + return 0; > + > + if (encoder->cu->unspecified_type.tag && tag_type == encoder->cu->unspecified_type.type) { > + // No provision for encoding this, turn it into void. > + return 0; > + } > + > + return type_id_off + tag_type; > +} > + > static int32_t btf_encoder__add_func_proto(struct btf_encoder *encoder, struct ftype *ftype, uint32_t type_id_off) > { > struct btf *btf = encoder->btf; > @@ -603,7 +616,7 @@ static int32_t btf_encoder__add_func_proto(struct btf_encoder *encoder, struct f > > /* add btf_type for func_proto */ > nr_params = ftype->nr_parms + (ftype->unspec_parms ? 1 : 0); > - type_id = ftype->tag.type == 0 ? 0 : type_id_off + ftype->tag.type; > + type_id = btf_encoder__tag_type(encoder, type_id_off, ftype->tag.type); > > id = btf__add_func_proto(btf, type_id); > if (id > 0) { > @@ -966,6 +979,15 @@ 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: > + /* Just don't encode this for now, converting anything with this type to void (0) instead. > + * > + * If we end up needing to encode this, one possible hack is to do as follows, as "const void". > + * > + * Returning zero means we skipped encoding a DWARF type. > + */ > + // btf_encoder__add_ref_type(encoder, BTF_KIND_CONST, 0, NULL, false); > + return 0; > default: > fprintf(stderr, "Unsupported DW_TAG_%s(0x%x): type: 0x%x\n", > dwarf_tag_name(tag->tag), tag->tag, ref_type_id); > @@ -1487,7 +1509,7 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct co > { > uint32_t type_id_off = btf__type_cnt(encoder->btf) - 1; > struct llvm_annotation *annot; > - int btf_type_id, tag_type_id; > + int btf_type_id, tag_type_id, skipped_types = 0; > uint32_t core_id; > struct function *fn; > struct tag *pos; > @@ -1510,8 +1532,13 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct co > cu__for_each_type(cu, core_id, pos) { > btf_type_id = btf_encoder__encode_tag(encoder, pos, type_id_off, conf_load); > > + if (btf_type_id == 0) { > + ++skipped_types; > + continue; > + } > + > if (btf_type_id < 0 || > - tag__check_id_drift(pos, core_id, btf_type_id, type_id_off)) { > + tag__check_id_drift(pos, core_id, btf_type_id + skipped_types, type_id_off)) { > err = -1; > goto out; > } -- - Arnaldo
