On 10/10/22 1:19 PM, Arnaldo Carvalho de Melo wrote:
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.RightThis 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 voidSince we don´t have how to encode this info in BTF, and from what wesaw, at least in this case:Built binutils from git://sourceware.org/git/binutils-gdb.git, then usedgcc'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.oContents 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: 0So we have that asm label encoded by GNU AS 2.39.50 as aDW_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.o15e20ce2324a:~/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 whengets 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) {
Why we need tag_type == encoder->cu->unspecified_type.type? Should we unconditionally convert an unspecified_type to btf type id 0?
+ // 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; }
