Re: [Mesa-dev] [PATCH 2/2] Don't use -fvisibilty=hidden on cygwin
On Tue, Apr 26, 2011 at 5:00 AM, Jon TURNEY jon.tur...@dronecode.org.uk wrote: Using -fvisibility=hidden makes the current cygwin gcc emit a warning warning: visibility attribute not supported in this configuration; ignored for every single non-static symbol $ make clean make 21 | grep ignored | wc -l 6457 This is pretty annoying and makes it hard to spot other errors and warnings in the compiler output. It's not clear how to fix this. Possibly the correct solution is explicitly decorate all symbols with macros which annotate the expected visibility and evaluate to attribute(hidden/default) or dllexport depending on the target, as suggested at [1], but this would be a lot of work and misses the main advantage of -fvisibility=hidden (that you don't have to explicitly annotate everything :-)), so I guess we are supposed to know when -fvisibility isn't going to be useful and not use it. [1] http://gcc.gnu.org/wiki/Visibility Alternatively, the configuration check could be made more complex to avoid using this flag is the target isn't ELF or using the flag generates a warning You could add -Werror to the CFLAGS used for the visibility test since any host that's throwing warnings for something so simple probably has issues with visibility. Something like: diff --git a/configure.ac b/configure.ac index 8989c2b..ec662a3 100644 --- a/configure.ac +++ b/configure.ac @@ -152,7 +152,7 @@ if test x$GCC = xyes; then save_CFLAGS=$CFLAGS AC_MSG_CHECKING([whether $CC supports -fvisibility=hidden]) VISIBILITY_CFLAGS=-fvisibility=hidden -CFLAGS=$CFLAGS $VISIBILITY_CFLAGS +CFLAGS=$CFLAGS $VISIBILITY_CFLAGS -Werror AC_LINK_IFELSE([AC_LANG_PROGRAM()], AC_MSG_RESULT([yes]), [VISIBILITY_CFLAGS=; AC_MSG_RESULT([no])]); Does that do the right thing? -- Dan ___ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
Re: [Mesa-dev] [PATCH 2/2] Don't use -fvisibilty=hidden on cygwin
On 27/04/2011 11:39, Dan Nicholson wrote: On Tue, Apr 26, 2011 at 5:00 AM, Jon TURNEY wrote: Alternatively, the configuration check could be made more complex to avoid using this flag is the target isn't ELF or using the flag generates a warning You could add -Werror to the CFLAGS used for the visibility test since any host that's throwing warnings for something so simple probably has issues with visibility. Something like: diff --git a/configure.ac b/configure.ac index 8989c2b..ec662a3 100644 --- a/configure.ac +++ b/configure.ac @@ -152,7 +152,7 @@ if test x$GCC = xyes; then save_CFLAGS=$CFLAGS AC_MSG_CHECKING([whether $CC supports -fvisibility=hidden]) VISIBILITY_CFLAGS=-fvisibility=hidden -CFLAGS=$CFLAGS $VISIBILITY_CFLAGS +CFLAGS=$CFLAGS $VISIBILITY_CFLAGS -Werror AC_LINK_IFELSE([AC_LANG_PROGRAM()], AC_MSG_RESULT([yes]), [VISIBILITY_CFLAGS=; AC_MSG_RESULT([no])]); Does that do the right thing? Yes, this works, and in fact this was the approach I initially tried, and seems more elegant. However, I was concerned about false negatives. As far as I can tell, nothing guarantees that the test program compiled by AC_LANG_PROGRAM() compiles without warnings, only without errors, so using -Werror might cause this test to fail for reasons unrelated to -fvisibility. Looking at this a bit more, though, a bit of googling seems to indicate we wouldn't be the first to use this construction, so perhaps it's ok :-) ___ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
[Mesa-dev] [PATCH 2/2] Don't use -fvisibilty=hidden on cygwin
Using -fvisibility=hidden makes the current cygwin gcc emit a warning warning: visibility attribute not supported in this configuration; ignored for every single non-static symbol $ make clean make 21 | grep ignored | wc -l 6457 This is pretty annoying and makes it hard to spot other errors and warnings in the compiler output. It's not clear how to fix this. Possibly the correct solution is explicitly decorate all symbols with macros which annotate the expected visibility and evaluate to attribute(hidden/default) or dllexport depending on the target, as suggested at [1], but this would be a lot of work and misses the main advantage of -fvisibility=hidden (that you don't have to explicitly annotate everything :-)), so I guess we are supposed to know when -fvisibility isn't going to be useful and not use it. [1] http://gcc.gnu.org/wiki/Visibility Alternatively, the configuration check could be made more complex to avoid using this flag is the target isn't ELF or using the flag generates a warning For the moment, I've gone for the crude solution of explicitly disabling the use of this flag for the cygwin target Signed-off-by: Jon TURNEY jon.tur...@dronecode.org.uk --- configure.ac |9 + 1 files changed, 9 insertions(+), 0 deletions(-) diff --git a/configure.ac b/configure.ac index 37ea5e7..b1e1de1 100644 --- a/configure.ac +++ b/configure.ac @@ -182,6 +182,15 @@ if test x$GXX = xyes; then CXXFLAGS=$CXXFLAGS -fno-strict-aliasing fi +dnl even if the compiler appears to support it, using visibility attributes isn't +dnl going to do anything useful currently on cygwin apart from emit lots of warnings +case $host_os in +cygwin*) +VISIBILITY_CFLAGS= +VISIBILITY_CXXFLAGS= +;; +esac + AC_SUBST([VISIBILITY_CFLAGS]) AC_SUBST([VISIBILITY_CXXFLAGS]) -- 1.7.4 ___ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
