From: Nathan Chancellor Date: Thu, 23 Jul 2026 00:09:43 +0000 (-0700) Subject: x86/boot/compressed: Disable jump tables X-Git-Tag: v7.2-rc5~10^2 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=4a9ec5ec9555ad62dc5b81a37ac946025c2ea002;p=thirdparty%2Fkernel%2Flinux.git x86/boot/compressed: Disable jump tables After a recent upstream LLVM change to start generating jump and lookup tables in switch statements in more instances [1], linking the compressed x86 boot image when CONFIG_KERNEL_ZSTD is enabled fails with: ld.lld: error: Unexpected run-time relocations (.rela) detected! Dumping the relocations in misc.o, which is the only file influenced by CONFIG_KERNEL_ZSTD in the decompressor, shows dynamic relocations to some string constants, which correspond to the string literals in the switch statement in handle_zstd_error(): Relocation section '.rela.data.rel.ro' at offset 0x277b0 contains 31 entries: Offset Info Type Symbol's Value Symbol's Name + Addend 0000000000000000 0000006600000001 R_X86_64_64 0000000000000000 .rodata.str1.1 + 73a 0000000000000008 0000006600000001 R_X86_64_64 0000000000000000 .rodata.str1.1 + 78e 0000000000000010 0000006600000001 R_X86_64_64 0000000000000000 .rodata.str1.1 + 78e 0000000000000018 0000006600000001 R_X86_64_64 0000000000000000 .rodata.str1.1 + 78e ... This optimization is problematic for the decompressor environment, as it is built as -fPIE without any explicit absolute references (as described at the top of misc.c) while not applying any dynamic relocations, hence the linker assertion. To opt out of this optimization, which is of little value in this special early boot code, and to mirror the other x86 startup code in arch/x86/boot/startup, disable jump tables in the decompressor. Signed-off-by: Nathan Chancellor Signed-off-by: Ingo Molnar Acked-by: Ard Biesheuvel Cc: Bill Wendling Cc: Justin Stitt Cc: Nick Desaulniers Cc: "H. Peter Anvin" Cc: Peter Zijlstra Cc: stable@vger.kernel.org Link: https://github.com/llvm/llvm-project/commit/fa02a6ed66b1700c996b49c96c6bc0eb014c9518 [1] Link: https://patch.msgid.link/20260722-x86-boot-compressed-disable-jt-clang-v2-1-7373d38482fb@kernel.org Closes: https://github.com/ClangBuiltLinux/linux/issues/2165 --- diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 07e0e64b9a98..06934f9691d6 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -27,6 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \ KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS) KBUILD_CFLAGS += $(CC_FLAGS_DIALECT) KBUILD_CFLAGS += -fno-strict-aliasing -fPIE +KBUILD_CFLAGS += -fno-jump-tables KBUILD_CFLAGS += -Wundef KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING cflags-$(CONFIG_X86_32) := -march=i386