# [PATCH] config.mak.dev: suppress C11 extension warning for Clang on Linux 3 messages from 2026-05-07 to 2026-05-10. Participants: Shardul Natu via GitGitGadget, Pablo, Junio C Hamano. Thread: https://gitlist.dev/t/65605 ## Shardul Natu via GitGitGadget, 2026-05-07 02:16 Subject: [PATCH] config.mak.dev: suppress C11 extension warning for Clang on Linux Message-ID: ``` From: Shnatu When building Git with Clang on Linux with DEVELOPER=1, the build fails because Clang treats C11 features used in glibc headers as extensions and raises errors due to -std=gnu99, -pedantic, and -Werror. Specifically, glibc's string.h uses _Generic (a C11 feature) in macros like strchr. When these macros are expanded in Git's C files, Clang warns about them being C11 extensions. GCC does not exhibit this behavior because it suppresses pedantic warnings for macros defined in system headers. To fix this, add -Wno-c11-extensions to DEVELOPER_CFLAGS when using Clang, but restrict it to Linux (uname_S == Linux). This suppresses the warning for glibc headers while keeping the build strict on other platforms (like macOS) to catch accidental C11 usage in Git's own code. Signed-off-by: Shnatu --- config.mak.dev: suppress C11 extension warning for Clang on Linux Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2291%2Fkiranani%2Fnext-2-v1 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2291/kiranani/next-2-v1 Pull-Request: https://github.com/git/git/pull/2291 config.mak.dev | 3 +++ 1 file changed, 3 insertions(+) diff --git a/config.mak.dev b/config.mak.dev index c8dcf78779..f1dcf4329a 100644 --- a/config.mak.dev +++ b/config.mak.dev @@ -87,6 +87,9 @@ endif # The bug was fixed in Apple clang 12. # ifneq ($(filter clang1,$(COMPILER_FEATURES)),) # if we are using clang +ifeq ($(uname_S),Linux) +DEVELOPER_CFLAGS += -Wno-c11-extensions +endif ifeq ($(uname_S),Darwin) # if we are on darwin ifeq ($(filter clang12,$(COMPILER_FEATURES)),) # if version < 12 DEVELOPER_CFLAGS += -Wno-missing-braces base-commit: 4f69b47b940100b02630f745a52f9d9850f122b2 -- gitgitgadget ``` ## Pablo, 2026-05-07 10:07 Subject: Re: [PATCH] config.mak.dev: suppress C11 extension warning for Clang on Linux Message-ID: In-Reply-To: ``` El jue, 7 may 2026 a las 4:16, Shardul Natu via GitGitGadget () escribió: > > From: Shnatu > > When building Git with Clang on Linux with DEVELOPER=1, the build fails > because Clang treats C11 features used in glibc headers as extensions > and raises errors due to -std=gnu99, -pedantic, and -Werror. Hi Shnatu! This is already being discussed at: https://lore.kernel.org/git/20260505-b4-pks-ci-tolerate-glibc-generic-v1-1-5786386fe512@pks.im/T/#u You might want to check out that thread. Hope this helps, -- Pablo > > Specifically, glibc's string.h uses _Generic (a C11 feature) in macros > like strchr. When these macros are expanded in Git's C files, Clang > warns about them being C11 extensions. > > GCC does not exhibit this behavior because it suppresses pedantic > warnings for macros defined in system headers. > > To fix this, add -Wno-c11-extensions to DEVELOPER_CFLAGS when using > Clang, but restrict it to Linux (uname_S == Linux). This suppresses > the warning for glibc headers while keeping the build strict on other > platforms (like macOS) to catch accidental C11 usage in Git's own code. > > Signed-off-by: Shnatu > --- > config.mak.dev: suppress C11 extension warning for Clang on Linux > > Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2291%2Fkiranani%2Fnext-2-v1 > Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2291/kiranani/next-2-v1 > Pull-Request: https://github.com/git/git/pull/2291 > > config.mak.dev | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/config.mak.dev b/config.mak.dev > index c8dcf78779..f1dcf4329a 100644 > --- a/config.mak.dev > +++ b/config.mak.dev > @@ -87,6 +87,9 @@ endif > # The bug was fixed in Apple clang 12. > # > ifneq ($(filter clang1,$(COMPILER_FEATURES)),) # if we are using clang > +ifeq ($(uname_S),Linux) > +DEVELOPER_CFLAGS += -Wno-c11-extensions > +endif > ifeq ($(uname_S),Darwin) # if we are on darwin > ifeq ($(filter clang12,$(COMPILER_FEATURES)),) # if version < 12 > DEVELOPER_CFLAGS += -Wno-missing-braces > > base-commit: 4f69b47b940100b02630f745a52f9d9850f122b2 > -- > gitgitgadget > ``` ## Junio C Hamano, 2026-05-10 22:21 Subject: Re: [PATCH] config.mak.dev: suppress C11 extension warning for Clang on Linux Message-ID: In-Reply-To: ``` Pablo writes: > El jue, 7 may 2026 a las 4:16, Shardul Natu via GitGitGadget > () escribió: >> >> From: Shnatu >> >> When building Git with Clang on Linux with DEVELOPER=1, the build fails >> because Clang treats C11 features used in glibc headers as extensions >> and raises errors due to -std=gnu99, -pedantic, and -Werror. > > Hi Shnatu! > This is already being discussed at: > https://lore.kernel.org/git/20260505-b4-pks-ci-tolerate-glibc-generic-v1-1-5786386fe512@pks.im/T/#u > > You might want to check out that thread. > > Hope this helps, Yes, they aim to solve the same issue, but the approach taken by this patch to use -Wno-c11-extensions on clang may be with less damage than the other approach that drops -std=gnu99 from Makefile. The other approach uses the equivalent of this patch on the meson side, so it may be doubly so that we should use -Wno-c11-extensions on both build systems, no? >> Specifically, glibc's string.h uses _Generic (a C11 feature) in macros >> like strchr. When these macros are expanded in Git's C files, Clang >> warns about them being C11 extensions. >> >> GCC does not exhibit this behavior because it suppresses pedantic >> warnings for macros defined in system headers. >> >> To fix this, add -Wno-c11-extensions to DEVELOPER_CFLAGS when using >> Clang, but restrict it to Linux (uname_S == Linux). This suppresses >> the warning for glibc headers while keeping the build strict on other >> platforms (like macOS) to catch accidental C11 usage in Git's own code. >> >> Signed-off-by: Shnatu >> --- >> config.mak.dev: suppress C11 extension warning for Clang on Linux >> >> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2291%2Fkiranani%2Fnext-2-v1 >> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2291/kiranani/next-2-v1 >> Pull-Request: https://github.com/git/git/pull/2291 >> >> config.mak.dev | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/config.mak.dev b/config.mak.dev >> index c8dcf78779..f1dcf4329a 100644 >> --- a/config.mak.dev >> +++ b/config.mak.dev >> @@ -87,6 +87,9 @@ endif >> # The bug was fixed in Apple clang 12. >> # >> ifneq ($(filter clang1,$(COMPILER_FEATURES)),) # if we are using clang >> +ifeq ($(uname_S),Linux) >> +DEVELOPER_CFLAGS += -Wno-c11-extensions >> +endif >> ifeq ($(uname_S),Darwin) # if we are on darwin >> ifeq ($(filter clang12,$(COMPILER_FEATURES)),) # if version < 12 >> DEVELOPER_CFLAGS += -Wno-missing-braces >> >> base-commit: 4f69b47b940100b02630f745a52f9d9850f122b2 >> -- >> gitgitgadget >> ```