In [1], linux introduced a note with type BUILD_COMPILER_LTO_INFO. If this note type exist, there is no need to scan .debug_abbrev section for cross-cu reference. With a kernel built with [1], the cus__merging_cu() overhead is about 3us for either lto or non-lto vmlinux. [1] https://lore.kernel.org/bpf/20210401012406.1800957-1-yhs@xxxxxx/ Signed-off-by: Yonghong Song <yhs@xxxxxx> --- dwarf_loader.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index bd23751..026d137 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -2501,8 +2501,37 @@ static int cus__load_debug_types(struct cus *cus, struct conf_load *conf, return 0; } -static bool cus__merging_cu(Dwarf *dw) +/* Match the define in linux:include/linux/elfnote.h */ +#define LINUX_ELFNOTE_BUILD_LTO 0x101 + +static bool cus__merging_cu(Dwarf *dw, Elf *elf) { + Elf_Scn *section = NULL; + while ((section = elf_nextscn(elf, section)) != 0) { + GElf_Shdr header; + if (!gelf_getshdr(section, &header)) + continue; + + if (header.sh_type != SHT_NOTE) + continue; + + Elf_Data *data = NULL; + while ((data = elf_getdata(section, data)) != 0) { + size_t name_off, desc_off, offset = 0; + GElf_Nhdr hdr; + while ((offset = gelf_getnote(data, offset, &hdr, &name_off, &desc_off)) != 0) { + if (hdr.n_type != LINUX_ELFNOTE_BUILD_LTO) + continue; + + /* owner is Linux */ + if (strcmp((char *)data->d_buf + name_off, "Linux") != 0) + continue; + + return *(int *)(data->d_buf + desc_off) != 0; + } + } + } + Dwarf_Off off = 0, noff; size_t cuhl; @@ -2649,7 +2678,7 @@ static int cus__load_module(struct cus *cus, struct conf_load *conf, } } - if (cus__merging_cu(dw)) { + if (cus__merging_cu(dw, elf)) { res = cus__merge_and_process_cu(cus, conf, mod, dw, elf, filename, build_id, build_id_len, type_cu ? &type_dcu : NULL); -- 2.30.2
