From 522397d05e7d4a7c30b91841492360336b24f833 Mon Sep 17 00:00:00 2001 From: Ihor Solodrai Date: Fri, 19 Dec 2025 10:18:25 -0800 Subject: resolve_btfids: Change in-place update with raw binary output 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. Change 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}.BTF_ids with .BTF_ids section data if it existed in ${1} * ${1}.BTF.base with .BTF.base section data for out-of-tree modules The execution of resolve_btfids and consumption of its output is orchestrated by scripts/gen-btf.sh introduced in this patch. The motivation for emitting binary data is that it allows simplifying resolve_btfids implementation by delegating ELF update to the $OBJCOPY tool [1], which is already widely used across the codebase. 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. The patch doesn't change this approach, only the implementation is a little different. Before this patch it worked as follows: * pahole consumed .tmp_vmlinux1 [2] and added .BTF section with llvm-objcopy [3] to it * then everything except the .BTF section was stripped from .tmp_vmlinux1 into a .tmp_vmlinux1.bpf.o object [2], later linked into vmlinux * resolve_btfids was executed later on vmlinux.unstripped [4], 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 kernel modules, creating a special .bpf.o file is not necessary, and so embedding of sections data produced by resolve_btfids is straightforward with objcopy. With this patch an ELF file becomes effectively read-only within resolve_btfids, which allows deleting elf_update() call and satellite code (like compressed_section_fix [5]). Endianness handling of .BTF_ids data is also changed. Previously the "flags" part of the section was bswapped in sets_patch() [6], 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://lore.kernel.org/bpf/131b4190-9c49-4f79-a99d-c00fac97fa44@linux.dev/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/link-vmlinux.sh?h=v6.18#n110 [3] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/tree/btf_encoder.c?h=v1.31#n1803 [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/link-vmlinux.sh?h=v6.18#n284 [5] https://lore.kernel.org/bpf/20200819092342.259004-1-jolsa@kernel.org/ [6] https://lore.kernel.org/bpf/cover.1707223196.git.vmalik@redhat.com/ Signed-off-by: Ihor Solodrai Signed-off-by: Andrii Nakryiko Tested-by: Alan Maguire Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20251219181825.1289460-3-ihor.solodrai@linux.dev --- scripts/Makefile.vmlinux | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'scripts/Makefile.vmlinux') diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux index cd788cac9d91..20a988f4fe0c 100644 --- a/scripts/Makefile.vmlinux +++ b/scripts/Makefile.vmlinux @@ -71,7 +71,7 @@ targets += vmlinux.unstripped .vmlinux.export.o vmlinux.unstripped: scripts/link-vmlinux.sh vmlinux.o .vmlinux.export.o $(KBUILD_LDS) FORCE +$(call if_changed_dep,link_vmlinux) ifdef CONFIG_DEBUG_INFO_BTF -vmlinux.unstripped: $(RESOLVE_BTFIDS) +vmlinux.unstripped: $(RESOLVE_BTFIDS) $(srctree)/scripts/gen-btf.sh endif ifdef CONFIG_BUILDTIME_TABLE_SORT -- cgit v1.2.3 From 6d60354ea2f90352b22039ed8371c4f4321df90e Mon Sep 17 00:00:00 2001 From: Ethan Zuo Date: Wed, 28 Jan 2026 14:37:51 +0800 Subject: kbuild: Fix permissions of modules.builtin.modinfo Currently, modules.builtin.modinfo is created with executable permissions (0755). This is because after commit 39cfd5b12160 ("kbuild: extract modules.builtin.modinfo from vmlinux.unstripped"), modules.builtin.modinfo is extracted from vmlinux.unstripped using objcopy. When extracting sections, objcopy inherits attributes from the source ELF file. Since modules.builtin.modinfo is a data file and not an executable, it should have regular file permissions (0644). The executable bit can trigger warnings in Debian's Lintian tool. Explicitly remove the executable bit after generation. Fixes: 39cfd5b12160 ("kbuild: extract modules.builtin.modinfo from vmlinux.unstripped") Signed-off-by: Ethan Zuo Link: https://patch.msgid.link/SY0P300MB0609F6916B24ADF65502940B9C91A@SY0P300MB0609.AUSP300.PROD.OUTLOOK.COM Signed-off-by: Nicolas Schier --- scripts/Makefile.vmlinux | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'scripts/Makefile.vmlinux') diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux index cd788cac9d91..276c3134a563 100644 --- a/scripts/Makefile.vmlinux +++ b/scripts/Makefile.vmlinux @@ -113,7 +113,8 @@ vmlinux: vmlinux.unstripped FORCE # what kmod expects to parse. quiet_cmd_modules_builtin_modinfo = GEN $@ cmd_modules_builtin_modinfo = $(cmd_objcopy); \ - sed -i 's/\x00\+$$/\x00/g' $@ + sed -i 's/\x00\+$$/\x00/g' $@; \ + chmod -x $@ OBJCOPYFLAGS_modules.builtin.modinfo := -j .modinfo -O binary -- cgit v1.2.3