From: Sami Tolvanen samitolvanen@google.com
[ Upstream commit 674d03f6bd6b0f8327f1a4920ff5893557facfbd ]
With CONFIG_GENDWARFKSYMS, um builds fail due to missing prototypes in asm/asm-prototypes.h. Add declarations for cmpxchg8b_emu and the exported checksum functions, including csum_partial_copy_generic as it's also exported.
Cc: Masahiro Yamada masahiroy@kernel.org Cc: linux-kbuild@vger.kernel.org Reported-by: kernel test robot lkp@intel.com Closes: https://lore.kernel.org/oe-kbuild-all/202503251216.lE4t9Ikj-lkp@intel.com/ Signed-off-by: Sami Tolvanen samitolvanen@google.com Link: https://patch.msgid.link/20250326190500.847236-2-samitolvanen@google.com Signed-off-by: Johannes Berg johannes.berg@intel.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES**
This commit should be backported to stable kernel trees based on the following analysis:
## Analysis
### Purpose and Context This commit fixes a build failure in the User Mode Linux (UM) architecture when `CONFIG_GENDWARFKSYMS` is enabled. The `CONFIG_GENDWARFKSYMS` feature is a new kernel build system enhancement for generating DWARF-based symbol versioning, which requires proper prototypes in `asm-prototypes.h` files to generate correct CRCs for exported symbols.
### Code Changes Analysis
**File 1: `arch/um/include/asm/asm-prototypes.h`** - **Before**: Only included the generic asm-prototypes.h - **After**: Added includes for `<asm/checksum.h>` and conditional declaration of `cmpxchg8b_emu()` for `CONFIG_UML_X86`
**File 2: `arch/x86/um/asm/checksum.h`** - **Before**: Only declared `csum_partial()` function - **After**: Added declaration for `csum_partial_copy_generic()` with a comment explaining it's for export type visibility
### Why This Should Be Backported
1. **Fixes Important Build Failures**: This directly addresses build failures when `CONFIG_GENDWARFKSYMS` is enabled for UM architecture, as confirmed by the kernel test robot report.
2. **Minimal Risk Changes**: - Only adds function declarations, no implementation changes - Changes are confined to UM architecture headers - No behavioral changes to existing code paths
3. **Follows Established Patterns**: Similar commits in the reference history (Similar Commit #1 and #5) that add missing prototypes to `asm-prototypes.h` files were marked as "YES" for backporting. This follows the exact same pattern.
4. **Critical Infrastructure Fix**: The `asm-prototypes.h` infrastructure is essential for proper symbol versioning. Missing prototypes can cause genksyms to segfault during build, making this a critical build system fix.
5. **Architecture-Specific Scope**: Changes are limited to UM architecture, reducing risk of regressions in other subsystems.
6. **Self-Contained**: The fix includes both the missing `cmpxchg8b_emu` prototype (conditional on `CONFIG_UML_X86`) and the checksum function declarations, making it complete.
### Comparison to Reference Commits - **Similar to Commit #1**: Adds missing prototypes for genksyms CRC generation (Status: YES) - **Similar to Commit #5**: Fixes missing prototypes causing build issues with symbol versioning (Status: YES) - **Unlike Commits #2, #3, #4**: This is not just a comment update or cleanup, but fixes actual build failures
The fix addresses a concrete build failure affecting users who enable `CONFIG_GENDWARFKSYMS` with UM, making it an important bugfix that meets stable tree criteria for backporting.
arch/um/include/asm/asm-prototypes.h | 5 +++++ arch/x86/um/asm/checksum.h | 3 +++ 2 files changed, 8 insertions(+)
diff --git a/arch/um/include/asm/asm-prototypes.h b/arch/um/include/asm/asm-prototypes.h index 5898a26daa0dd..408b31d591279 100644 --- a/arch/um/include/asm/asm-prototypes.h +++ b/arch/um/include/asm/asm-prototypes.h @@ -1 +1,6 @@ #include <asm-generic/asm-prototypes.h> +#include <asm/checksum.h> + +#ifdef CONFIG_UML_X86 +extern void cmpxchg8b_emu(void); +#endif diff --git a/arch/x86/um/asm/checksum.h b/arch/x86/um/asm/checksum.h index b07824500363f..ddc144657efad 100644 --- a/arch/x86/um/asm/checksum.h +++ b/arch/x86/um/asm/checksum.h @@ -20,6 +20,9 @@ */ extern __wsum csum_partial(const void *buff, int len, __wsum sum);
+/* Do not call this directly. Declared for export type visibility. */ +extern __visible __wsum csum_partial_copy_generic(const void *src, void *dst, int len); + /** * csum_fold - Fold and invert a 32bit checksum. * sum: 32bit unfolded sum