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Message-ID: <CAErzpmvsgSDe-QcWH8SFFErL6y3p3zrqNri5-UHJ9iK2ChyiBw@mail.gmail.com>
Date: Fri, 28 Nov 2025 11:20:33 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
Nicolas Schier <nicolas.schier@...ux.dev>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>,
Justin Stitt <justinstitt@...gle.com>, Alan Maguire <alan.maguire@...cle.com>, bpf@...r.kernel.org,
dwarves@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kbuild@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 4/4] resolve_btfids: change in-place update
with raw binary output
On Fri, Nov 28, 2025 at 2:53 AM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
>
> Currently resolve_btfids updates .BTF_ids section of an ELF file
> in-place, based on the contents of provided BTF, usually within the
> same input file, and optionally a BTF base.
>
> This patch changes resolve_btfids behavior to enable BTF
> transformations as part of its main operation. To achieve this
> in-place ELF write in resolve_btfids is replaced with generation of
> the following binaries:
> * ${1}.btf with .BTF section data
> * ${1}.distilled_base.btf with .BTF.base section data (for
> out-of-tree modules)
> * ${1}.btf_ids with .BTF_ids section data, if it exists in ${1}
>
> The execution of resolve_btfids and consumption of its output is
> orchestrated by scripts/gen-btf.sh introduced in this patch.
>
> The rationale for this approach is that updating ELF in-place with
> libelf API is complicated and bug-prone, especially in the context of
> the kernel build. On the other hand applying objcopy to manipulate ELF
> sections is simpler and more reliable.
>
> There are two distinct paths for BTF generation and resolve_btfids
> application in the kernel build: for vmlinux and for kernel modules.
>
> For the vmlinux binary a .BTF section is added in a roundabout way to
> ensure correct linking (details below). The patch doesn't change this
> approach, only the implementation is a little different.
>
> Before this patch it worked like follows:
>
> * pahole consumed .tmp_vmlinux1 [1] and added .BTF section with
> llvm-objcopy [2] to it
> * then everything except the .BTF section was stripped from .tmp_vmlinux1
> into a .tmp_vmlinux1.bpf.o object [1], later linked into vmlinux
> * resolve_btfids was executed later on vmlinux.unstripped [3],
> updating it in-place
>
> After this patch gen-btf.sh implements the following:
>
> * pahole consumes .tmp_vmlinux1 and produces a *detached* file with
> raw BTF data
> * resolve_btfids consumes .tmp_vmlinux1 and detached BTF to produce
> (potentially modified) .BTF, and .BTF_ids sections data
> * a .tmp_vmlinux1.bpf.o object is then produced with objcopy copying
> BTF output of resolve_btfids
> * .BTF_ids data gets embedded into vmlinux.unstripped in
> link-vmlinux.sh by objcopy --update-section
>
> For the kernel modules creating special .bpf.o file is not necessary,
> and so embedding of sections data produced by resolve_btfids is
> straightforward with the objcopy.
>
> With this patch an ELF file becomes effectively read-only within
> resolve_btfids, which allows to delete elf_update() call and satelite
> code (like compressed_section_fix [4]).
>
> Endianness handling of .BTF_ids data is also changed. Previously the
> "flags" part of the section was bswapped in sets_patch() [5], and then
> Elf_Type was modified before elf_update() to signal to libelf that
> bswap may be necessary. With this patch we explicitly bswap entire
> data buffer on load and on dump.
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/scripts/link-vmlinux.sh#n115
> [2] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/tree/btf_encoder.c#n1835
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/scripts/link-vmlinux.sh#n285
> [4] https://lore.kernel.org/bpf/20200819092342.259004-1-jolsa@kernel.org/
> [5] https://lore.kernel.org/bpf/cover.1707223196.git.vmalik@redhat.com/
>
> Signed-off-by: Ihor Solodrai <ihor.solodrai@...ux.dev>
> ---
> MAINTAINERS | 1 +
> scripts/Makefile.modfinal | 5 +-
> scripts/gen-btf.sh | 167 ++++++++++++++++++++
> scripts/link-vmlinux.sh | 42 +-----
> tools/bpf/resolve_btfids/main.c | 218 +++++++++++++++++----------
> tools/testing/selftests/bpf/Makefile | 5 +
> 6 files changed, 317 insertions(+), 121 deletions(-)
> create mode 100755 scripts/gen-btf.sh
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 48aabeeed029..5cd34419d952 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4672,6 +4672,7 @@ F: net/sched/act_bpf.c
> F: net/sched/cls_bpf.c
> F: samples/bpf/
> F: scripts/bpf_doc.py
> +F: scripts/gen-btf.sh
> F: scripts/Makefile.btf
> F: scripts/pahole-version.sh
> F: tools/bpf/
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 542ba462ed3e..3862fdfa1267 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -38,9 +38,8 @@ quiet_cmd_btf_ko = BTF [M] $@
> cmd_btf_ko = \
> if [ ! -f $(objtree)/vmlinux ]; then \
> printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
> - else \
> - LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) $(MODULE_PAHOLE_FLAGS) --btf_base $(objtree)/vmlinux $@; \
> - $(RESOLVE_BTFIDS) -b $(objtree)/vmlinux $@; \
> + else \
> + $(srctree)/scripts/gen-btf.sh --btf_base $(objtree)/vmlinux $@; \
> fi;
>
> # Same as newer-prereqs, but allows to exclude specified extra dependencies
> diff --git a/scripts/gen-btf.sh b/scripts/gen-btf.sh
> new file mode 100755
> index 000000000000..2dfb7ab289ca
> --- /dev/null
> +++ b/scripts/gen-btf.sh
> @@ -0,0 +1,167 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2025 Meta Platforms, Inc. and affiliates.
> +#
> +# This script generates BTF data for the provided ELF file.
> +#
> +# Kernel BTF generation involves these conceptual steps:
> +# 1. pahole generates BTF from DWARF data
> +# 2. resolve_btfids applies kernel-specific btf2btf
> +# transformations and computes data for .BTF_ids section
> +# 3. the result gets linked/objcopied into the target binary
> +#
> +# How step (3) should be done differs between vmlinux, and
> +# kernel modules, which is the primary reason for the existence
> +# of this script.
> +#
> +# For modules the script expects vmlinux passed in as --btf_base.
> +# Generated .BTF, .BTF.base and .BTF_ids sections become embedded
> +# into the input ELF file with objcopy.
> +#
> +# For vmlinux the input file remains unchanged and two files are produced:
> +# - ${1}.btf.o ready for linking into vmlinux
> +# - ${1}.btf_ids with .BTF_ids data blob
> +# This output is consumed by scripts/link-vmlinux.sh
> +
> +set -e
> +
> +usage()
> +{
> + echo "Usage: $0 [--btf_base <file>] <target ELF file>"
> + exit 1
> +}
> +
> +BTF_BASE=""
> +
> +while [ $# -gt 0 ]; do
> + case "$1" in
> + --btf_base)
> + BTF_BASE="$2"
> + shift 2
> + ;;
> + -*)
> + echo "Unknown option: $1" >&2
> + usage
> + ;;
> + *)
> + break
> + ;;
> + esac
> +done
> +
> +if [ $# -ne 1 ]; then
> + usage
> +fi
> +
> +ELF_FILE="$1"
> +shift
> +
> +is_enabled() {
> + grep -q "^$1=y" ${objtree}/include/config/auto.conf
> +}
> +
> +info()
> +{
> + printf " %-7s %s\n" "${1}" "${2}"
> +}
> +
> +case "${KBUILD_VERBOSE}" in
> +*1*)
> + set -x
> + ;;
> +esac
> +
> +if ! is_enabled CONFIG_DEBUG_INFO_BTF; then
> + exit 0
> +fi
> +
> +gen_btf_data()
> +{
> + info BTF "${ELF_FILE}"
> + btf1="${ELF_FILE}.btf.1"
> + ${PAHOLE} -J ${PAHOLE_FLAGS} \
> + ${BTF_BASE:+--btf_base ${BTF_BASE}} \
> + --btf_encode_detached=${btf1} \
> + "${ELF_FILE}"
> +
> + info BTFIDS "${ELF_FILE}"
> + RESOLVE_BTFIDS_OPTS=""
> + if is_enabled CONFIG_WERROR; then
> + RESOLVE_BTFIDS_OPTS+=" --fatal_warnings "
> + fi
> + if [ -n "${KBUILD_VERBOSE}" ]; then
> + RESOLVE_BTFIDS_OPTS+=" -v "
> + fi
> + ${RESOLVE_BTFIDS} ${RESOLVE_BTFIDS_OPTS} \
> + ${BTF_BASE:+--btf_base ${BTF_BASE}} \
> + --btf ${btf1} "${ELF_FILE}"
> +}
> +
> +gen_btf_o()
> +{
> + local btf_data=${ELF_FILE}.btf.o
> +
> + # Create ${btf_data} which contains just .BTF section but no symbols. Add
> + # SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
> + # deletes all symbols including __start_BTF and __stop_BTF, which will
> + # be redefined in the linker script.
> + info OBJCOPY "${btf_data}"
> + echo "" | ${CC} -c -x c -o ${btf_data} -
> + ${OBJCOPY} --add-section .BTF=${ELF_FILE}.btf \
> + --set-section-flags .BTF=alloc,readonly ${btf_data}
> + ${OBJCOPY} --only-section=.BTF --strip-all ${btf_data}
> +
> + # Change e_type to ET_REL so that it can be used to link final vmlinux.
> + # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
> + if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> + et_rel='\0\1'
> + else
> + et_rel='\1\0'
> + fi
> + printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 status=none
> +}
> +
> +embed_btf_data()
> +{
> + info OBJCOPY "${ELF_FILE}"
> + ${OBJCOPY} --add-section .BTF=${ELF_FILE}.btf ${ELF_FILE}
> +
> + # a module might not have a .BTF_ids or .BTF.base section
> + local btf_base="${ELF_FILE}.distilled_base.btf"
> + if [ -f "${btf_base}" ]; then
> + ${OBJCOPY} --add-section .BTF.base=${btf_base} ${ELF_FILE}
> + fi
> + local btf_ids="${ELF_FILE}.btf_ids"
> + if [ -f "${btf_ids}" ]; then
> + ${OBJCOPY} --update-section .BTF_ids=${btf_ids} ${ELF_FILE}
> + fi
> +}
> +
> +cleanup()
> +{
> + rm -f "${ELF_FILE}.btf.1"
> + rm -f "${ELF_FILE}.btf"
> + if [ "${BTFGEN_MODE}" = "module" ]; then
> + rm -f "${ELF_FILE}.distilled_base.btf"
> + rm -f "${ELF_FILE}.btf_ids"
> + fi
> +}
> +trap cleanup EXIT
> +
> +BTFGEN_MODE="vmlinux"
> +if [ -n "${BTF_BASE}" ]; then
> + BTFGEN_MODE="module"
> +fi
> +
> +gen_btf_data
> +
> +case "${BTFGEN_MODE}" in
> +vmlinux)
> + gen_btf_o
> + ;;
> +module)
> + embed_btf_data
> + ;;
> +esac
> +
> +exit 0
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 433849ff7529..5bea8795f96d 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -105,34 +105,6 @@ vmlinux_link()
> ${kallsymso} ${btf_vmlinux_bin_o} ${arch_vmlinux_o} ${ldlibs}
> }
>
> -# generate .BTF typeinfo from DWARF debuginfo
> -# ${1} - vmlinux image
> -gen_btf()
> -{
> - local btf_data=${1}.btf.o
> -
> - info BTF "${btf_data}"
> - LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
> -
> - # Create ${btf_data} which contains just .BTF section but no symbols. Add
> - # SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
> - # deletes all symbols including __start_BTF and __stop_BTF, which will
> - # be redefined in the linker script. Add 2>/dev/null to suppress GNU
> - # objcopy warnings: "empty loadable segment detected at ..."
> - ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> - --strip-all ${1} "${btf_data}" 2>/dev/null
> - # Change e_type to ET_REL so that it can be used to link final vmlinux.
> - # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
> - if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> - et_rel='\0\1'
> - else
> - et_rel='\1\0'
> - fi
> - printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 status=none
> -
> - btf_vmlinux_bin_o=${btf_data}
> -}
> -
> # Create ${2}.o file with all symbols from the ${1} object file
> kallsyms()
> {
> @@ -204,6 +176,7 @@ if is_enabled CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX; then
> fi
>
> btf_vmlinux_bin_o=
> +btfids_vmlinux=
> kallsymso=
> strip_debug=
> generate_map=
> @@ -224,11 +197,13 @@ if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then
> fi
>
> if is_enabled CONFIG_DEBUG_INFO_BTF; then
> - if ! gen_btf .tmp_vmlinux1; then
> + if ! ${srctree}/scripts/gen-btf.sh .tmp_vmlinux1; then
> echo >&2 "Failed to generate BTF for vmlinux"
> echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
> exit 1
> fi
> + btf_vmlinux_bin_o=.tmp_vmlinux1.btf.o
> + btfids_vmlinux=.tmp_vmlinux1.btf_ids
> fi
>
> if is_enabled CONFIG_KALLSYMS; then
> @@ -281,14 +256,9 @@ fi
>
> vmlinux_link "${VMLINUX}"
>
> -# fill in BTF IDs
> if is_enabled CONFIG_DEBUG_INFO_BTF; then
> - info BTFIDS "${VMLINUX}"
> - RESOLVE_BTFIDS_ARGS=""
> - if is_enabled CONFIG_WERROR; then
> - RESOLVE_BTFIDS_ARGS=" --fatal_warnings "
> - fi
> - ${RESOLVE_BTFIDS} ${RESOLVE_BTFIDS_ARGS} "${VMLINUX}"
> + info OBJCOPY ${btfids_vmlinux}
> + ${OBJCOPY} --update-section .BTF_ids=${btfids_vmlinux} ${VMLINUX}
> fi
>
> mksysmap "${VMLINUX}" System.map
> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
> index c60d303ca6ed..b8df6256e29e 100644
> --- a/tools/bpf/resolve_btfids/main.c
> +++ b/tools/bpf/resolve_btfids/main.c
> @@ -71,9 +71,11 @@
> #include <fcntl.h>
> #include <errno.h>
> #include <linux/btf_ids.h>
> +#include <linux/kallsyms.h>
> #include <linux/rbtree.h>
> #include <linux/zalloc.h>
> #include <linux/err.h>
> +#include <linux/limits.h>
> #include <bpf/btf.h>
> #include <bpf/libbpf.h>
> #include <subcmd/parse-options.h>
> @@ -124,6 +126,7 @@ struct object {
>
> struct btf *btf;
> struct btf *base_btf;
> + bool distilled_base;
>
> struct {
> int fd;
> @@ -308,42 +311,16 @@ static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
> return btf_id;
> }
>
> -/* Older libelf.h and glibc elf.h might not yet define the ELF compression types. */
> -#ifndef SHF_COMPRESSED
> -#define SHF_COMPRESSED (1 << 11) /* Section with compressed data. */
> -#endif
> -
> -/*
> - * The data of compressed section should be aligned to 4
> - * (for 32bit) or 8 (for 64 bit) bytes. The binutils ld
> - * sets sh_addralign to 1, which makes libelf fail with
> - * misaligned section error during the update:
> - * FAILED elf_update(WRITE): invalid section alignment
> - *
> - * While waiting for ld fix, we fix the compressed sections
> - * sh_addralign value manualy.
> - */
> -static int compressed_section_fix(Elf *elf, Elf_Scn *scn, GElf_Shdr *sh)
> +static void bswap_32_data(void *data, u32 nr_bytes)
> {
> - int expected = gelf_getclass(elf) == ELFCLASS32 ? 4 : 8;
> + u32 cnt, i;
> + u32 *ptr;
>
> - if (!(sh->sh_flags & SHF_COMPRESSED))
> - return 0;
> + cnt = nr_bytes / sizeof(u32);
> + ptr = data;
>
> - if (sh->sh_addralign == expected)
> - return 0;
> -
> - pr_debug2(" - fixing wrong alignment sh_addralign %u, expected %u\n",
> - sh->sh_addralign, expected);
> -
> - sh->sh_addralign = expected;
> -
> - if (gelf_update_shdr(scn, sh) == 0) {
> - pr_err("FAILED cannot update section header: %s\n",
> - elf_errmsg(-1));
> - return -1;
> - }
> - return 0;
> + for (i = 0; i < cnt; i++)
> + ptr[i] = bswap_32(ptr[i]);
> }
>
> static int elf_collect(struct object *obj)
> @@ -364,7 +341,7 @@ static int elf_collect(struct object *obj)
>
> elf_version(EV_CURRENT);
>
> - elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
> + elf = elf_begin(fd, ELF_C_READ_MMAP_PRIVATE, NULL);
> if (!elf) {
> close(fd);
> pr_err("FAILED cannot create ELF descriptor: %s\n",
> @@ -427,21 +404,20 @@ static int elf_collect(struct object *obj)
> obj->efile.symbols_shndx = idx;
> obj->efile.strtabidx = sh.sh_link;
> } else if (!strcmp(name, BTF_IDS_SECTION)) {
> + /*
> + * If target endianness differs from host, we need to bswap32
> + * the .BTF_ids section data on load, because .BTF_ids has
> + * Elf_Type = ELF_T_BYTE, and so libelf returns data buffer in
> + * the target endiannes. We repeat this on dump.
> + */
> + if (obj->efile.encoding != ELFDATANATIVE) {
> + pr_debug("bswap_32 .BTF_ids data from target to host endianness\n");
> + bswap_32_data(data->d_buf, data->d_size);
> + }
> obj->efile.idlist = data;
> obj->efile.idlist_shndx = idx;
> obj->efile.idlist_addr = sh.sh_addr;
> - } else if (!strcmp(name, BTF_BASE_ELF_SEC)) {
> - /* If a .BTF.base section is found, do not resolve
> - * BTF ids relative to vmlinux; resolve relative
> - * to the .BTF.base section instead. btf__parse_split()
> - * will take care of this once the base BTF it is
> - * passed is NULL.
> - */
> - obj->base_btf_path = NULL;
> }
> -
> - if (compressed_section_fix(elf, scn, &sh))
> - return -1;
> }
>
> return 0;
> @@ -545,6 +521,13 @@ static int symbols_collect(struct object *obj)
> return 0;
> }
>
> +static inline bool is_envvar_set(const char *var_name)
> +{
> + const char *value = getenv(var_name);
> +
> + return value && value[0] != '\0';
> +}
> +
> static int load_btf(struct object *obj)
> {
> struct btf *base_btf = NULL, *btf = NULL;
> @@ -571,6 +554,20 @@ static int load_btf(struct object *obj)
> obj->base_btf = base_btf;
> obj->btf = btf;
>
> + if (obj->base_btf && is_envvar_set("KBUILD_EXTMOD")) {
> + err = btf__distill_base(obj->btf, &base_btf, &btf);
> + if (err) {
> + pr_err("FAILED to distill base BTF: %s\n", strerror(errno));
> + goto out_err;
> + }
> +
> + btf__free(obj->btf);
> + btf__free(obj->base_btf);
> + obj->btf = btf;
> + obj->base_btf = base_btf;
> + obj->distilled_base = true;
> + }
> +
> return 0;
>
> out_err:
> @@ -744,24 +741,6 @@ static int sets_patch(struct object *obj)
> */
> BUILD_BUG_ON((u32 *)set8->pairs != &set8->pairs[0].id);
> qsort(set8->pairs, set8->cnt, sizeof(set8->pairs[0]), cmp_id);
> -
> - /*
> - * When ELF endianness does not match endianness of the
> - * host, libelf will do the translation when updating
> - * the ELF. This, however, corrupts SET8 flags which are
> - * already in the target endianness. So, let's bswap
> - * them to the host endianness and libelf will then
> - * correctly translate everything.
> - */
> - if (obj->efile.encoding != ELFDATANATIVE) {
> - int i;
> -
> - set8->flags = bswap_32(set8->flags);
> - for (i = 0; i < set8->cnt; i++) {
> - set8->pairs[i].flags =
> - bswap_32(set8->pairs[i].flags);
> - }
> - }
> break;
> case BTF_ID_KIND_SYM:
> default:
> @@ -778,8 +757,6 @@ static int sets_patch(struct object *obj)
>
> static int symbols_patch(struct object *obj)
> {
> - off_t err;
> -
> if (__symbols_patch(obj, &obj->structs) ||
> __symbols_patch(obj, &obj->unions) ||
> __symbols_patch(obj, &obj->typedefs) ||
> @@ -790,20 +767,77 @@ static int symbols_patch(struct object *obj)
> if (sets_patch(obj))
> return -1;
>
> - /* Set type to ensure endian translation occurs. */
> - obj->efile.idlist->d_type = ELF_T_WORD;
> + return 0;
> +}
>
> - elf_flagdata(obj->efile.idlist, ELF_C_SET, ELF_F_DIRTY);
> +static int dump_raw_data(const char *out_path, const void *data, u32 size)
> +{
> + int fd, ret;
>
> - err = elf_update(obj->efile.elf, ELF_C_WRITE);
> - if (err < 0) {
> - pr_err("FAILED elf_update(WRITE): %s\n",
> - elf_errmsg(-1));
> + fd = open(out_path, O_WRONLY | O_CREAT | O_TRUNC, 0640);
> + if (fd < 0) {
> + pr_err("Couldn't open %s for writing\n", out_path);
> + return fd;
> + }
> +
> + ret = write(fd, data, size);
> + if (ret < 0 || ret != size) {
> + pr_err("Failed to write data to %s\n", out_path);
> + close(fd);
> + unlink(out_path);
> + return -1;
> + }
> +
> + close(fd);
> + pr_debug("Dumped %lu bytes of data to %s\n", size, out_path);
> +
> + return 0;
> +}
> +
> +static int dump_raw_btf_ids(struct object *obj, const char *out_path)
> +{
> + Elf_Data *data = obj->efile.idlist;
> + int fd, err;
> +
> + if (!data || !data->d_buf) {
> + pr_debug("%s has no BTF_ids data to dump\n", obj->path);
> + return 0;
> + }
> +
> + /*
> + * If target endianness differs from host, we need to bswap32 the
> + * .BTF_ids section data before dumping so that the output is in
> + * target endianness.
> + */
> + if (obj->efile.encoding != ELFDATANATIVE) {
> + pr_debug("bswap_32 .BTF_ids data from host to target endianness\n");
> + bswap_32_data(data->d_buf, data->d_size);
> + }
> +
> + err = dump_raw_data(out_path, data->d_buf, data->d_size);
> + if (err)
> + return -1;
> +
> + return 0;
> +}
> +
> +static int dump_raw_btf(struct btf *btf, const char *out_path)
> +{
> + const void *raw_btf_data;
> + u32 raw_btf_size;
> + int fd, err;
> +
> + raw_btf_data = btf__raw_data(btf, &raw_btf_size);
> + if (raw_btf_data == NULL) {
> + pr_err("btf__raw_data() failed\n");
> + return -1;
> }
>
> - pr_debug("update %s for %s\n",
> - err >= 0 ? "ok" : "failed", obj->path);
> - return err < 0 ? -1 : 0;
> + err = dump_raw_data(out_path, raw_btf_data, raw_btf_size);
> + if (err)
> + return -1;
> +
> + return 0;
> }
>
> static const char * const resolve_btfids_usage[] = {
> @@ -824,6 +858,7 @@ int main(int argc, const char **argv)
> .funcs = RB_ROOT,
> .sets = RB_ROOT,
> };
> + char out_path[PATH_MAX];
> bool fatal_warnings = false;
> struct option btfid_options[] = {
> OPT_INCR('v', "verbose", &verbose,
> @@ -836,7 +871,7 @@ int main(int argc, const char **argv)
> "turn warnings into errors"),
> OPT_END()
> };
> - int err = -1;
> + int err = -1, path_len;
>
> argc = parse_options(argc, argv, btfid_options, resolve_btfids_usage,
> PARSE_OPT_STOP_AT_NON_OPTION);
> @@ -844,6 +879,11 @@ int main(int argc, const char **argv)
> usage_with_options(resolve_btfids_usage, btfid_options);
>
> obj.path = argv[0];
> + strcpy(out_path, obj.path);
> + path_len = strlen(out_path);
> +
> + if (load_btf(&obj))
> + goto out;
>
> if (elf_collect(&obj))
> goto out;
> @@ -854,23 +894,37 @@ int main(int argc, const char **argv)
> */
> if (obj.efile.idlist_shndx == -1 ||
> obj.efile.symbols_shndx == -1) {
> - pr_debug("Cannot find .BTF_ids or symbols sections, nothing to do\n");
> - err = 0;
> - goto out;
> + pr_debug("Cannot find .BTF_ids or symbols sections, skip symbols resolution\n");
> + goto dump_btf;
> }
>
> if (symbols_collect(&obj))
> goto out;
>
> - if (load_btf(&obj))
> - goto out;
> -
> if (symbols_resolve(&obj))
> goto out;
>
> if (symbols_patch(&obj))
> goto out;
>
> + out_path[path_len] = '\0';
> + strcat(out_path, ".btf_ids");
> + if (dump_raw_btf_ids(&obj, out_path))
> + goto out;
> +
> +dump_btf:
> + out_path[path_len] = '\0';
> + strcat(out_path, ".btf");
> + if (dump_raw_btf(obj.btf, out_path))
> + goto out;
> +
> + if (obj.base_btf && obj.distilled_base) {
> + out_path[path_len] = '\0';
> + strcat(out_path, ".distilled_base.btf");
> + if (dump_raw_btf(obj.base_btf, out_path))
> + goto out;
> + }
> +
> if (!(fatal_warnings && warnings))
> err = 0;
> out:
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index bac22265e7ff..ec7e2a7721c7 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -4,6 +4,7 @@ include ../../../scripts/Makefile.arch
> include ../../../scripts/Makefile.include
>
> CXX ?= $(CROSS_COMPILE)g++
> +OBJCOPY ?= $(CROSS_COMPILE)objcopy
>
> CURDIR := $(abspath .)
> TOOLSDIR := $(abspath ../../..)
> @@ -716,6 +717,10 @@ $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS) \
> $$(call msg,BINARY,,$$@)
> $(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) $$(LLVM_LDLIBS) $$(LDFLAGS) $$(LLVM_LDFLAGS) -o $$@
> $(Q)$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@
> + $(Q)if [ -f $$@...f_ids ]; then \
> + $(OBJCOPY) --update-section .BTF_ids=$$@...f_ids $$@; \
I encountered a resolve_btfids self-test failure when enabling the
BTF sorting feature, with the following error output:
All error logs:
resolve_symbols:PASS:resolve 0 nsec
test_resolve_btfids:PASS:id_check 0 nsec
test_resolve_btfids:PASS:id_check 0 nsec
test_resolve_btfids:FAIL:id_check wrong ID for T (7 != 5)
#369 resolve_btfids:FAIL
The root cause is that prog_tests/resolve_btfids.c retrieves type IDs
from btf_data.bpf.o and compares them against the IDs in test_progs.
However, while the IDs in test_progs are sorted, those in btf_data.bpf.o
remain in their original unsorted state, causing the validation to fail.
This presents two potential solutions:
1. Update the relevant .BTF.* section datas in btf_data.bpf.o, including
the .BTF and .BTF.ext sections
2. Modify prog_tests/resolve_btfids.c to retrieve IDs from test_progs.btf
instead. However, I discovered that test_progs.btf is deleted in the
subsequent code section.
What do you think of it?
Thanks,
Donglin
> + fi
> + $(Q)rm -f $$@...f_ids $$@...f
> $(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/$(USE_BOOTSTRAP)bpftool \
> $(OUTPUT)/$(if $2,$2/)bpftool
>
> --
> 2.52.0
>
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