Re: [PATCH] x86/mm: fix objtool failure with KMSAN enabled
Ilya Leoshkevich <[email protected]>
| Newsgroups | dev.linux.lists.llvm,org.kernel.vger.linux-kernel,org.kvack.linux-mm |
|---|---|
| Message-ID | <[email protected]> |
On 7/1/26 14:51, Dmitry Voytik wrote:
> 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 <folio_zero_user+0x817>
>
> 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 <[email protected]>
> ---
> arch/x86/include/asm/page_64.h | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
FWIW I just bumped into this build issue; this patch helped and the
resulting kernel booted.
Config: https://pastebin.com/B6GedVDL
Tested-by: Ilya Leoshkevich <[email protected]>