| Message ID | 20211114212437.1466695-2-sandals@crustytoothpaste.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add a test balloon for C99 | expand |
On Sun, Nov 14 2021, brian m. carlson wrote: > The C99 standard was released in January 1999, now 22 years ago. It > provides a variety of useful features, including variadic arguments for > macros, declarations after statements, variable length arrays, and a > wide variety of other useful features, many of which we already use. > > We'd like to take advantage of these features, but we want to be > cautious. As far as we know, all major compilers now support C99 or a > later C standard, such as C11 or C17. POSIX has required C99 support as > a requirement for the 2001 revision, so we can safely assume any POSIX > system which we are interested in supporting has C99. I like this direction. > Sparse is also updated with a reference to the gnu99 standard, without > which it defaults to C89. Do we really need it in SPARSE_FLAGS though... > @@ -1204,7 +1204,7 @@ endif > # Set CFLAGS, LDFLAGS and other *FLAGS variables. These might be > # tweaked by config.* below as well as the command-line, both of > # which'll override these defaults. > -CFLAGS = -g -O2 -Wall > +CFLAGS = -g -O2 -Wall -std=gnu99 > LDFLAGS = > CC_LD_DYNPATH = -Wl,-rpath, > BASIC_CFLAGS = -I. > @@ -1215,7 +1215,7 @@ ARFLAGS = rcs > PTHREAD_CFLAGS = Since $(CFLAGS) ends up in: ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(CPPFLAGS) $(CFLAGS) ... > # For the 'sparse' target > -SPARSE_FLAGS ?= > +SPARSE_FLAGS ?= -std=gnu99 > SP_EXTRA_FLAGS = -Wno-universal-initializer ... and this will be used for this rule: $(SP_OBJ): %.sp: %.c %.o $(QUIET_SP)cgcc -no-compile $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) \ -Wsparse-error \ $(SPARSE_FLAGS) $(SP_EXTRA_FLAGS) $< [...] I.e. unless it needs to be later on the command-line the $(ALL_CFLAGS) should put it there already. Also (and this pre-dates this patch) it's unfortunate that CFLAGS is a mixed bag of compiler tweaking and "mandatory" flags. I think the below would be a better approach, particurly since our own config.mak.uname will override CFLAGS in some cases, and probably everyone who works on git to any degree has a local config.mak which sets it to something already. But why gnu99 and not c99? diff --git a/Makefile b/Makefile index 12be39ac497..7470d627165 100644 --- a/Makefile +++ b/Makefile @@ -1204,10 +1204,14 @@ endif # Set CFLAGS, LDFLAGS and other *FLAGS variables. These might be # tweaked by config.* below as well as the command-line, both of # which'll override these defaults. +# +# The MANDATORY_CFLAGS can be similarly overridden, but really +# shouldn't. CFLAGS = -g -O2 -Wall LDFLAGS = CC_LD_DYNPATH = -Wl,-rpath, -BASIC_CFLAGS = -I. +BASIC_CFLAGS = +MANDATORY_CFLAGS = -I. -std=gnu99 BASIC_LDFLAGS = # library flags @@ -1249,7 +1253,7 @@ ALL_COMMANDS_TO_INSTALL += git-upload-archive$(X) ALL_COMMANDS_TO_INSTALL += git-upload-pack$(X) endif -ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(CPPFLAGS) $(CFLAGS) +ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(CPPFLAGS) $(CFLAGS) $(MANDATORY_CFLAGS) ALL_LDFLAGS = $(LDFLAGS) comma := ,
On 2021-11-15 at 01:14:42, Ævar Arnfjörð Bjarmason wrote: > > On Sun, Nov 14 2021, brian m. carlson wrote: > > > The C99 standard was released in January 1999, now 22 years ago. It > > provides a variety of useful features, including variadic arguments for > > macros, declarations after statements, variable length arrays, and a > > wide variety of other useful features, many of which we already use. > > > > We'd like to take advantage of these features, but we want to be > > cautious. As far as we know, all major compilers now support C99 or a > > later C standard, such as C11 or C17. POSIX has required C99 support as > > a requirement for the 2001 revision, so we can safely assume any POSIX > > system which we are interested in supporting has C99. > > I like this direction. I felt like a test balloon would go over better than a wholesale changeover. I feel confident we can make this change, and we may even in the not too distant future be able to switch to C11. > > Sparse is also updated with a reference to the gnu99 standard, without > > which it defaults to C89. > > Do we really need it in SPARSE_FLAGS though... > > > @@ -1204,7 +1204,7 @@ endif > > # Set CFLAGS, LDFLAGS and other *FLAGS variables. These might be > > # tweaked by config.* below as well as the command-line, both of > > # which'll override these defaults. > > -CFLAGS = -g -O2 -Wall > > +CFLAGS = -g -O2 -Wall -std=gnu99 > > LDFLAGS = > > CC_LD_DYNPATH = -Wl,-rpath, > > BASIC_CFLAGS = -I. > > @@ -1215,7 +1215,7 @@ ARFLAGS = rcs > > PTHREAD_CFLAGS = > > Since $(CFLAGS) ends up in: > > ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(CPPFLAGS) $(CFLAGS) > > ... > > > # For the 'sparse' target > > -SPARSE_FLAGS ?= > > +SPARSE_FLAGS ?= -std=gnu99 > > SP_EXTRA_FLAGS = -Wno-universal-initializer > > ... and this will be used for this rule: > > $(SP_OBJ): %.sp: %.c %.o > $(QUIET_SP)cgcc -no-compile $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) \ > -Wsparse-error \ > $(SPARSE_FLAGS) $(SP_EXTRA_FLAGS) $< [...] > > I.e. unless it needs to be later on the command-line the $(ALL_CFLAGS) > should put it there already. I added it to SPARSE_FLAGS before adding it into CFLAGS, so I can look into dropping it from the former. > Also (and this pre-dates this patch) it's unfortunate that CFLAGS is a > mixed bag of compiler tweaking and "mandatory" flags. I think the below > would be a better approach, particurly since our own config.mak.uname > will override CFLAGS in some cases, and probably everyone who works on > git to any degree has a local config.mak which sets it to something > already. We don't want to do this, because some people are using other compilers (i.e., neither GCC nor clang) that need different options. We definitely do want them to be able to override these values as necessary. I believe config.mak.uname does this in some cases for certain Unix systems. > But why gnu99 and not c99? I'll explain in the commit message in a reroll, but essentially, because we do in some case use GNUisms when we're working with GCC. Right now those are mostly limited to providing C99 features on C89, but I'd like to leave the opportunity open for us to do this in the future.
On Sun, Nov 14, 2021 at 4:27 PM brian m. carlson <sandals@crustytoothpaste.net> wrote: > +#if __STDC_VERSION__ - 0 < 199901L > +/* > + * Git is in a testing period for mandatory C99 support in the compiler. If > + * your compiler is reasonably recent, you can try to enable C99 support (or, > + * for MSVC, C11 support). If you encounter a problem and can't enable C99 > + * support with your compiler and don't have access to one with this support, > + * such as GCC or Clang, you can remove this #if directive, but please report > + * the details of your system to git@vger.kernel.org. > + */ > +#error "Required C99 support is in a test phase. Please see git-compat-util.h for more details." You don't need to encapsulate the #error message in double quotes.
On 2021-11-15 at 03:16:02, Eric Sunshine wrote: > On Sun, Nov 14, 2021 at 4:27 PM brian m. carlson > <sandals@crustytoothpaste.net> wrote: > > +#if __STDC_VERSION__ - 0 < 199901L > > +/* > > + * Git is in a testing period for mandatory C99 support in the compiler. If > > + * your compiler is reasonably recent, you can try to enable C99 support (or, > > + * for MSVC, C11 support). If you encounter a problem and can't enable C99 > > + * support with your compiler and don't have access to one with this support, > > + * such as GCC or Clang, you can remove this #if directive, but please report > > + * the details of your system to git@vger.kernel.org. > > + */ > > +#error "Required C99 support is in a test phase. Please see git-compat-util.h for more details." > > You don't need to encapsulate the #error message in double quotes. Technically, I believe in this case you are correct. The C standard specifies this as pp-tokens, which means one or more preprocessing tokens, and from my brief overview of the draft standard, it appears that this meets that definition. (I could be wrong, though.) _However_, there are some cases where quoting is required, such as when apostrophes appear, and although we don't have that case here, there are some compilers which are very strict about what they do or don't allow in an #error statement, or which are just broken, and as such, in my experience, it is safer and more portable to always quote it. I definitely don't want us to have the problem that we break an otherwise functional compiler by causing it to choke on the #error directive it doesn't need to execute.
Hi brian, On Sun, 14 Nov 2021, brian m. carlson wrote: > diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt > index fd1399c440..91e8525fa9 100644 > --- a/contrib/buildsystems/CMakeLists.txt > +++ b/contrib/buildsystems/CMakeLists.txt > @@ -208,7 +208,7 @@ endif() > if(CMAKE_C_COMPILER_ID STREQUAL "MSVC") > set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG ${CMAKE_BINARY_DIR}) > set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE ${CMAKE_BINARY_DIR}) > - add_compile_options(/MP) > + add_compile_options(/MP /std:c11) > endif() > > #default behaviour If we do this, we also need the following patch, to ensure that `FLEX_ARRAY` is once again defined in a way that is acceptable for MS Visual C: -- snipsnap -- commit 9043470c19170643d1f74d6767a0df5d72e6c35c Author: Johannes Schindelin <Johannes.Schindelin@gmx.de> Date: Mon Nov 22 12:39:40 2021 +0100 fixup??? git-compat-util: add a test balloon for C99 support This seems to be required to define `FLEX_ARRAY` in a manner that MSVC in C11 mode accepts. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> diff --git a/git-compat-util.h b/git-compat-util.h index cba8ad260043..fcde3588172f 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -45,7 +45,7 @@ /* * See if our compiler is known to support flexible array members. */ -#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) && (!defined(__SUNPRO_C) || (__SUNPRO_C > 0x580)) +#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) && !defined(_MSC_VER) && (!defined(__SUNPRO_C) || (__SUNPRO_C > 0x580)) # define FLEX_ARRAY /* empty */ #elif defined(__GNUC__) # if (__GNUC__ >= 3)
diff --git a/Makefile b/Makefile index 12be39ac49..22d9e67542 100644 --- a/Makefile +++ b/Makefile @@ -1204,7 +1204,7 @@ endif # Set CFLAGS, LDFLAGS and other *FLAGS variables. These might be # tweaked by config.* below as well as the command-line, both of # which'll override these defaults. -CFLAGS = -g -O2 -Wall +CFLAGS = -g -O2 -Wall -std=gnu99 LDFLAGS = CC_LD_DYNPATH = -Wl,-rpath, BASIC_CFLAGS = -I. @@ -1215,7 +1215,7 @@ ARFLAGS = rcs PTHREAD_CFLAGS = # For the 'sparse' target -SPARSE_FLAGS ?= +SPARSE_FLAGS ?= -std=gnu99 SP_EXTRA_FLAGS = -Wno-universal-initializer # For informing GIT-BUILD-OPTIONS of the SANITIZE=leak target diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt index fd1399c440..91e8525fa9 100644 --- a/contrib/buildsystems/CMakeLists.txt +++ b/contrib/buildsystems/CMakeLists.txt @@ -208,7 +208,7 @@ endif() if(CMAKE_C_COMPILER_ID STREQUAL "MSVC") set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG ${CMAKE_BINARY_DIR}) set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE ${CMAKE_BINARY_DIR}) - add_compile_options(/MP) + add_compile_options(/MP /std:c11) endif() #default behaviour @@ -600,7 +600,6 @@ endif() list(REMOVE_DUPLICATES excluded_progs) list(REMOVE_DUPLICATES PROGRAMS_BUILT) - foreach(p ${excluded_progs}) list(APPEND EXCLUSION_PROGS --exclude-program ${p} ) endforeach() diff --git a/git-compat-util.h b/git-compat-util.h index d70ce14286..6d995bdc0f 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -1,6 +1,18 @@ #ifndef GIT_COMPAT_UTIL_H #define GIT_COMPAT_UTIL_H +#if __STDC_VERSION__ - 0 < 199901L +/* + * Git is in a testing period for mandatory C99 support in the compiler. If + * your compiler is reasonably recent, you can try to enable C99 support (or, + * for MSVC, C11 support). If you encounter a problem and can't enable C99 + * support with your compiler and don't have access to one with this support, + * such as GCC or Clang, you can remove this #if directive, but please report + * the details of your system to git@vger.kernel.org. + */ +#error "Required C99 support is in a test phase. Please see git-compat-util.h for more details." +#endif + #ifdef USE_MSVC_CRTDBG /* * For these to work they must appear very early in each
The C99 standard was released in January 1999, now 22 years ago. It provides a variety of useful features, including variadic arguments for macros, declarations after statements, variable length arrays, and a wide variety of other useful features, many of which we already use. We'd like to take advantage of these features, but we want to be cautious. As far as we know, all major compilers now support C99 or a later C standard, such as C11 or C17. POSIX has required C99 support as a requirement for the 2001 revision, so we can safely assume any POSIX system which we are interested in supporting has C99. Even MSVC, long a holdout against modern C, now supports both C11 and C17 with an appropriate update. Moreover, even if people are using an older version of MSVC on these systems, they will generally need some implementation of the standard Unix utilities for the testsuite, and GNU coreutils, the most common option, has required C99 since 2009. Therefore, we can safely assume that a suitable version of GCC or clang is available to users even if their version of MSVC is not sufficiently capable. Let's add a test balloon to git-compat-util.h to see if anyone is using an older compiler. We'll add a comment telling people how to enable this functionality on GCC and Clang, even though modern versions of both will automatically do the right thing, and ask people still experiencing a problem to report that to us on the list. Note that C89 compilers don't provide the __STDC_VERSION__ macro, so we use a well-known hack of using "- 0". On compilers with this macro, it doesn't change the value, and on C89 compilers, the macro will be replaced with nothing, and our value will be 0. Sparse is also updated with a reference to the gnu99 standard, without which it defaults to C89. Update the cmake configuration to require C11 for MSVC. We do this because this will make MSVC to use C11, since it does not explicitly support C99. We do this with a compiler options because setting the C_STANDARD option does not work in our CI on MSVC and at the moment, we don't want to require C11 for Unix compilers. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> --- Makefile | 4 ++-- contrib/buildsystems/CMakeLists.txt | 3 +-- git-compat-util.h | 12 ++++++++++++ 3 files changed, 15 insertions(+), 4 deletions(-)