From: Linus Torvalds torvalds@linux-foundation.org
[ Upstream commit 550ccb178de2f379f5e1a1833dd6f4bdafef4b68 ]
This is the follow-up to commit a79be02bba5c ("Fix mis-uses of 'cc-option' for warning disablement") where I mentioned that the best fix would be to just make 'cc-option' a bit smarter, and work for all compiler options, including the '-Wno-xyzzy' pattern that it used to accept unknown options for.
It turns out that fixing cc-option is pretty straightforward: just rewrite any '-Wno-xyzzy' option pattern to use '-Wxyzzy' instead for testing.
That makes the whole artificial distinction between 'cc-option' and 'cc-disable-warning' go away, and we can happily forget about the odd build rule that you have to treat compiler options that disable warnings specially.
The 'cc-disable-warning' helper remains as a backwards compatibility syntax for now, but is implemented in terms of the new and improved cc-option.
Acked-by: Masahiro Yamada masahiroy@kernel.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Arnd Bergmann arnd@arndb.de Cc: Stephen Rothwell sfr@canb.auug.org.au Cc: Thomas Weißschuh linux@weissschuh.net Cc: Nathan Chancellor nathan@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org ---
I can see an example of the problem on line 48: `-Wno-sign-compare` is being added directly instead of using `cc-disable-warning`. Now let me analyze the specific changes in the commit to understand what the fix does. Based on my analysis of the commit "Make 'cc-option' work correctly for the -Wno-xyzzy pattern", here is my assessment: **YES** This commit should be backported to stable kernel trees. Here's my detailed analysis: ## Analysis of the Code Changes The commit makes a crucial fix to the `cc-option` and `cc-disable-warning` functions in `scripts/Makefile.compiler`. The key changes are: 1. **In `__cc-option` function (line 45)**: Changed from: ```makefile $(1) -Werror $(2) $(3) -c -x c /dev/null -o "$$TMP",$(3),$(4) ``` to: ```makefile $(1) -Werror $(2) $(3:-Wno-%=-W%) -c -x c /dev/null -o "$$TMP",$(3),$(4) ``` 2. **In `cc-disable-warning` function (line 60)**: Simplified from: ```makefile cc-disable-warning = $(if $(call cc-option,-W$(strip $1)),-Wno-$(strip $1)) ``` to: ```makefile cc-disable-warning = $(call cc- option,-Wno-$(strip $1)) ``` ## Why This Should Be Backported ### 1. **Fixes a Fundamental Build System Bug** The bug is that GCC silently accepts unknown `-Wno-*` options and only warns about them when there are other warnings in the source. This means `cc-option` would incorrectly return "supported" for unsupported warning disable flags, leading to build warnings that shouldn't exist. ### 2. **Improves Build System Reliability** The fix ensures that build-time compiler feature detection works correctly across all supported compiler versions, preventing spurious warnings that could confuse developers and automated build systems. ### 3. **Minimal Risk of Regression** - The change is contained to the build system macros - It makes the behavior more correct rather than changing functionality - The fix is elegant: it transforms `-Wno-xyzzy` to `-Wxyzzy` for testing, then uses the original form if supported - No actual kernel code is affected, only the build logic ### 4. **Affects Critical Infrastructure Code** From my examination of the kernel repository, `cc-disable-warning` and `cc- option` are used extensively throughout the kernel build system. The fix ensures these fundamental macros work correctly across all architectures and configurations. ### 5. **Follows Stable Tree Criteria** - **Important bug fix**: Yes, fixes incorrect compiler option detection - **Minimal risk**: Yes, only changes build macros, no functional code changes - **Contained scope**: Yes, limited to `scripts/Makefile.compiler` - **No architectural changes**: Correct, just fixes existing functionality ### 6. **Historical Precedent** Looking at the similar commits provided, commits that fix build system issues and compiler option handling (like the similar commits marked "NO" but for different reasons) are generally good candidates when they fix fundamental problems rather than just optimization cleanups. The commit addresses a real problem where the build system could accept invalid compiler options, leading to confusing warnings. This type of fundamental correctness fix is exactly what stable trees are meant to include.
scripts/Makefile.compiler | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler index 75356d2acc0b5..47ab407f73ec2 100644 --- a/scripts/Makefile.compiler +++ b/scripts/Makefile.compiler @@ -43,7 +43,7 @@ as-instr = $(call try-run,\ # __cc-option # Usage: MY_CFLAGS += $(call __cc-option,$(CC),$(MY_CFLAGS),-march=winchip-c6,-march=i586) __cc-option = $(call try-run,\ - $(1) -Werror $(2) $(3) -c -x c /dev/null -o "$$TMP",$(3),$(4)) + $(1) -Werror $(2) $(3:-Wno-%=-W%) -c -x c /dev/null -o "$$TMP",$(3),$(4))
# cc-option # Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586) @@ -57,7 +57,7 @@ cc-option-yn = $(if $(call cc-option,$1),y,n)
# cc-disable-warning # Usage: cflags-y += $(call cc-disable-warning,unused-but-set-variable) -cc-disable-warning = $(if $(call cc-option,-W$(strip $1)),-Wno-$(strip $1)) +cc-disable-warning = $(call cc-option,-Wno-$(strip $1))
# gcc-min-version # Usage: cflags-$(call gcc-min-version, 70100) += -foo