Makefile.extrawarn: Move -Wunaligned-access to W=1

PATCH In review Nathan Chancellor 3 participants 4 messages Feb 2, 2022 – Feb 8, 2022

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Nathan Chancellor

author maintainer

2022-02-02 23:07 UTC #0 lore raw

PATCH v2 1/1 Makefile.extrawarn: Move -Wunaligned-access to W=1

-Wunaligned-access is a new warning in clang that is default enabled for arm and arm64 under certain circumstances within the clang frontend (see LLVM commit below). On v5.17-rc2, an ARCH=arm allmodconfig build shows 1284 total/70 unique instances of this warning (most of the instances are in header files), which is quite noisy.

To keep a normal build green through CONFIG_WERROR, only show this warning with W=1, which will allow automated build systems to catch new instances of the warning so that the total number can be driven down to zero eventually since catching unaligned accesses at compile time would be generally useful.

Cc [email protected]

Link https://github.com/llvm/llvm-project/commit/35737df4dcd28534bd3090157c224c19b501278a

Link https://github.com/ClangBuiltLinux/linux/issues/1569

Link https://github.com/ClangBuiltLinux/linux/issues/1576

Signed-off-by Nathan Chancellor <[email protected]>

---

v1 -> v2: https://lore.kernel.org/r/[email protected]/

* Move to W=1 instead of W=2 so that new instances are caught (Arnd).
* Add links to the ClangBuiltLinux issue tracker.

 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)

scripts/Makefile.extrawarn +1 -0

index d53825503874..8be892887d71 100644
@@ -51,6 +51,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
+KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
 endif
 
 endif

base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c

Signature · 1 line

2.35.1

Nick Desaulniers

Reviewed-by on v2 1/1

2022-02-02 23:12 UTC #1 lore raw

Quoted 13 lines · Nathan Chancellor

-Wunaligned-access is a new warning in clang that is default enabled for arm and arm64 under certain circumstances within the clang frontend (see LLVM commit below). On v5.17-rc2, an ARCH=arm allmodconfig build shows 1284 total/70 unique instances of this warning (most of the instances are in header files), which is quite noisy.
To keep a normal build green through CONFIG_WERROR, only show this warning with W=1, which will allow automated build systems to catch new instances of the warning so that the total number can be driven down to zero eventually since catching unaligned accesses at compile time would be generally useful.

Quoted 5 lines

Cc [email protected]
Link https://github.com/llvm/llvm-project/commit/35737df4dcd28534bd3090157c224c19b501278a
Link https://github.com/ClangBuiltLinux/linux/issues/1569
Link https://github.com/ClangBuiltLinux/linux/issues/1576
Signed-off-by Nathan Chancellor <[email protected]>

Thanks to you and Arnd for working out whether this is important to pursue. Sounds like it is.

Reviewed-by Nick Desaulniers <[email protected]>

Quoted 27 lines

---
v1 -> v2: https://lore.kernel.org/r/[email protected]/
* Move to W=1 instead of W=2 so that new instances are caught (Arnd).
* Add links to the ClangBuiltLinux issue tracker.
 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)
scripts/Makefile.extrawarn +1 -0
index d53825503874..8be892887d71 100644
@@ -51,6 +51,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
+KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
 endif
 
 endif
base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c --
2.35.1

Signature · 2 lines

Thanks,
~Nick Desaulniers

Masahiro Yamada

2022-02-08 04:24 UTC #2 lore raw

Quoted 21 lines · Nick Desaulniers

Quoted 13 lines · Nathan Chancellor
-Wunaligned-access is a new warning in clang that is default enabled for arm and arm64 under certain circumstances within the clang frontend (see LLVM commit below). On v5.17-rc2, an ARCH=arm allmodconfig build shows 1284 total/70 unique instances of this warning (most of the instances are in header files), which is quite noisy.
To keep a normal build green through CONFIG_WERROR, only show this warning with W=1, which will allow automated build systems to catch new instances of the warning so that the total number can be driven down to zero eventually since catching unaligned accesses at compile time would be generally useful.
Quoted 5 lines
Cc [email protected]
Link https://github.com/llvm/llvm-project/commit/35737df4dcd28534bd3090157c224c19b501278a
Link https://github.com/ClangBuiltLinux/linux/issues/1569
Link https://github.com/ClangBuiltLinux/linux/issues/1576
Signed-off-by Nathan Chancellor <[email protected]>

Quoted 5 lines

Thanks to you and Arnd for working out whether this is important to pursue. Sounds like it is.
Reviewed-by Nick Desaulniers <[email protected]>
Quoted 1 line
---

I assume this should be considered as a bug fix to avoid the error for the combination of CONFIG_WERROR=y and the latest Clang.

Applied to linux-kbuild/fixes.
Thanks.

Quoted 31 lines

Quoted 22 lines
v1 -> v2: https://lore.kernel.org/r/[email protected]/
* Move to W=1 instead of W=2 so that new instances are caught (Arnd).
* Add links to the ClangBuiltLinux issue tracker.
 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)
scripts/Makefile.extrawarn +1 -0
index d53825503874..8be892887d71 100644
@@ -51,6 +51,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
+KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
 endif
 
 endif
Quoted 4 lines
base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c --
2.35.1
--
Thanks,
~Nick Desaulniers

Signature · 2 lines

Best Regards
Masahiro Yamada

Nathan Chancellor

author maintainer

2022-02-08 16:04 UTC #3 lore raw

Quoted 29 lines · Masahiro Yamada

Quoted 21 lines · Nick Desaulniers
Quoted 13 lines · Nathan Chancellor
-Wunaligned-access is a new warning in clang that is default enabled for arm and arm64 under certain circumstances within the clang frontend (see LLVM commit below). On v5.17-rc2, an ARCH=arm allmodconfig build shows 1284 total/70 unique instances of this warning (most of the instances are in header files), which is quite noisy.
To keep a normal build green through CONFIG_WERROR, only show this warning with W=1, which will allow automated build systems to catch new instances of the warning so that the total number can be driven down to zero eventually since catching unaligned accesses at compile time would be generally useful.
Quoted 5 lines
Cc [email protected]
Link https://github.com/llvm/llvm-project/commit/35737df4dcd28534bd3090157c224c19b501278a
Link https://github.com/ClangBuiltLinux/linux/issues/1569
Link https://github.com/ClangBuiltLinux/linux/issues/1576
Signed-off-by Nathan Chancellor <[email protected]>
Quoted 5 lines
Thanks to you and Arnd for working out whether this is important to pursue. Sounds like it is.
Reviewed-by Nick Desaulniers <[email protected]>
Quoted 1 line
---

Quoted 6 lines

I assume this should be considered as a bug fix to avoid the error for the combination of CONFIG_WERROR=y and the latest Clang.
Applied to linux-kbuild/fixes.
Thanks.

Yes, this is what I was hoping for! Thank you, I'll try to make that more clear in the future.

Cheers,
Nathan

Quoted 37 lines

Quoted 31 lines
Quoted 22 lines
v1 -> v2: https://lore.kernel.org/r/[email protected]/
* Move to W=1 instead of W=2 so that new instances are caught (Arnd).
* Add links to the ClangBuiltLinux issue tracker.
 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)
scripts/Makefile.extrawarn +1 -0
index d53825503874..8be892887d71 100644
@@ -51,6 +51,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
+KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
 endif
 
 endif
Quoted 4 lines
base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c --
2.35.1
--
Thanks,
~Nick Desaulniers
Signature · 2 lines
Best Regards
Masahiro Yamada