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Peter Anvin" , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Marco Elver , x86@kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, llvm@lists.linux.dev, Dmitry Voytik Subject: [PATCH] x86/mm: fix objtool failure with KMSAN enabled Date: Wed, 1 Jul 2026 14:51:51 +0200 Message-ID: <20260701125151.352632-1-voytikd@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This patch fixes broken builds with defconfig + CONFIG_KMSAN + CONFIG_DEBUG_INFO_*. To reproduce the issue before the fix: make mrproper make LLVM=1 defconfig ./scripts/config -e CONFIG_KMSAN \ -e CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT make LLVM=1 olddefconfig make LLVM=1 -j(nproc) vmlinux ... LD vmlinux.o vmlinux.o: warning: objtool: folio_zero_user+0x801: undefined stack state vmlinux.o: error: objtool: folio_zero_user+0x801: unknown CFA base reg -1 make[2]: *** [scripts/Makefile.vmlinux_o:76: vmlinux.o] Error 255 objtool in verbose mode shows how the frame pointer is omitted: make LLVM=1 OBJTOOL_VERBOSE=1 -j(nproc) vmlinux ... b15a2c: folio_zero_user+0x7fc xor %eax,%eax b15a2e: folio_zero_user+0x7fe mov %rcx,%rsp b15a31: folio_zero_user+0x801 mov %r14,%rdi b15a34: folio_zero_user+0x804 mov %rbx,%rcx b15a37: folio_zero_user+0x807 call 0xb15a3c <__clear_pages_unrol After the fix, the frame pointer is back: b15a37: 31 c0 xor %eax,%eax b15a39: 48 89 ec mov %rbp,%rsp b15a3c: 4c 89 f7 mov %r14,%rdi b15a3f: 48 89 d9 mov %rbx,%rcx b15a42: e8 00 00 00 00 call b15a47 It seems the issue was introduced by commit 54a6b89a3db2 ("x86/mm: simplify clear_page_*") The actual fix is to revert the change how ASM_CALL_CONSTRAINT is positioned. Additionally, reintroduce asm_inline to prevent potential compiler rejection of inlining. Link: https://lore.kernel.org/CAAX90H2_RPnZL_dFYN7cQF6yt-wAweKKSx2=6e2aZ0kv+Pm+NQ@mail.gmail.com Signed-off-by: Dmitry Voytik --- arch/x86/include/asm/page_64.h | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h index 1895c207f629..de8604f0a3a1 100644 --- a/arch/x86/include/asm/page_64.h +++ b/arch/x86/include/asm/page_64.h @@ -100,12 +100,13 @@ static inline void clear_pages(void *addr, unsigned int npages) * __clear_pages_unrolled() are part of the inline asm register * specification. */ - asm volatile(ALTERNATIVE_2("call __clear_pages_unrolled", - "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD, - "rep stosb", X86_FEATURE_ERMS) - : "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT - : "a" (0) - : "cc", "memory"); + asm_inline volatile( + ALTERNATIVE_2("call __clear_pages_unrolled", + "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD, + "rep stosb", X86_FEATURE_ERMS) + : ASM_CALL_CONSTRAINT, "+c"(len), "+D"(addr) + : "a"(0) + : "cc", "memory"); } #define clear_pages clear_pages -- 2.54.0