From: Ard Biesheuvel Date: Mon, 9 Dec 2024 09:41:06 +0000 (+0100) Subject: x86/boot/64: Fix spurious undefined reference when CONFIG_X86_5LEVEL=n, on GCC-12 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=35aafa1d41cee0d3d50164561bca34befc1d9ce3;p=users%2Fdwmw2%2Flinux.git x86/boot/64: Fix spurious undefined reference when CONFIG_X86_5LEVEL=n, on GCC-12 In __startup_64(), the bool 'la57' can only assume the 'true' value if CONFIG_X86_5LEVEL is enabled in the build, and generally, the compiler can make this inference at build time, and elide any references to the symbol 'level4_kernel_pgt', which may be undefined if 'la57' is false. As it turns out, GCC 12 gets this wrong sometimes, and gives up with a build error: ld: arch/x86/kernel/head64.o: in function `__startup_64': head64.c:(.head.text+0xbd): undefined reference to `level4_kernel_pgt' even though the reference is in unreachable code. Fix this by duplicating the IS_ENABLED(CONFIG_X86_5LEVEL) in the conditional that tests the value of 'la57'. Reported-by: kernel test robot Signed-off-by: Ard Biesheuvel Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20241209094105.762857-2-ardb+git@google.com Closes: https://lore.kernel.org/oe-kbuild-all/202412060403.efD8Kgb7-lkp@intel.com/ --- diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 54f9a8faf212d..22c9ba305ac17 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -186,7 +186,7 @@ unsigned long __head __startup_64(unsigned long p2v_offset, pgd = &RIP_REL_REF(early_top_pgt)->pgd; pgd[pgd_index(__START_KERNEL_map)] += load_delta; - if (la57) { + if (IS_ENABLED(CONFIG_X86_5LEVEL) && la57) { p4d = (p4dval_t *)&RIP_REL_REF(level4_kernel_pgt); p4d[MAX_PTRS_PER_P4D - 1] += load_delta;