[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed|2020-01-27 00:00:00 |2020-01-30 Ever confirmed|0 |1 --- Comment #10 from Jonathan Wakely --- Another interpretation would be that it's simply user error to request a specific POSIX version and an incompatible C standard. If POSIX:2008 doesn't define things that C11 requires, you can't combine POSIX:2008 and C11. And POSIX doesn't define what *anything* means for a C++ program, so arguably using _XOPEN_SOURCE at all in C++ is undefined. If your POSIX implementation gives it a useful meaning, great, but if not and the macro breaks your C++ code, don't define the macro. Either way, how the OS interprets and responds to macros like _XOPEN_SOURCE is out of libstdc++'s hands. If the OS decides that _XOPEN_SOURCE=600 and C++17 are incompatible, there's only so much libstdc++ can do. Something like this should work though: #if __cplusplus >= 201703L && defined(_GLIBCXX_HAVE_ALIGNED_ALLOC) # if defined __APPLE__ && defined _XOPEN_VERSION // see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 extern "C" void* aligned_alloc(size_t, size_t); # else using ::aligned_alloc; # endif #endif Confirming as a bug, because we'll need that for previous releases of macOS anyway, but please do report this to Apple too.
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469
--- Comment #9 from Jonathan Wakely ---
(In reply to Karen from comment #8)
> Thanks for the explanation.
>
> In fact it doesn't work even for -D_XOPEN_SOURCE=700 as the latest POSIX
> edition doesn't specify the aligned_alloc function.
But it is defined by C11 and C++17, so if you compile with -std=c11 or
-std=c++17 (which will set __STDC_VERSION or __cplusplus respectively) then the
OS should declare aligned_alloc.
> On the other hand I don't observe that _XOPEN_SOURCE affects the __cplusplus
> macro:
I didn't say it changes the value of it, I said it overrides it. Look in
where the declaration of aligned_alloc is guarded by:
#if (__DARWIN_C_LEVEL >= __DARWIN_C_FULL) && \
((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) || \
(defined(__cplusplus) && __cplusplus >= 201703L))
This means if _DARWIN_C_LEVEL is below "full" (which happens when
_XOPENS_SOURCE is defined) then aligned_alloc will never be declared, even when
the C or C++ language dialect requires it.
In my not so humble opinion that first && should be || instead, so that
aligned_alloc is declared if the level is "full" or greater, **or** if it's
required by the language standard that is in use.
> One can argue, but this can be considered a libstdc++ issue that it is
> affected by the macro that defines the C functions availability.
But you get exactly the same problem compiling this C program with -std=c11,
where libstdc++ is completely irrelevant and there are no GCC headers used:
#define _XOPEN_SOURCE 600
#include
int main() { free(aligned_alloc(4, 4)); }
This warns about aligned_alloc being implicitly declared, because the macOS
header fails to declare it.
This is an Apple bug, please report it to radar.
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 --- Comment #8 from Karen --- Thanks for the explanation. In fact it doesn't work even for -D_XOPEN_SOURCE=700 as the latest POSIX edition doesn't specify the aligned_alloc function. On the other hand I don't observe that _XOPEN_SOURCE affects the __cplusplus macro: % cat
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 Jonathan Wakely changed: What|Removed |Added Status|WAITING |UNCONFIRMED Ever confirmed|1 |0 --- Comment #7 from Jonathan Wakely --- Thanks. This seems to be an Mac OS X feature, not a bug. Selecting a specific POSIX version overrides the __STDC_VERSION and __cplusplus values, and so names from newer POSIX standards (like aligned_alloc) are not available. IMO that is wrong, but it seems to be an intentional property of the OS X system headers. Which means that you can't combine -std=c++2a with -D_XOPEN_SOURCE=500. It produces an impossible combination where names required to exist by one standard are required to _not_ exist by the other standard. You could try reporting a radar bug and see if Apple really do consider this correct behaviour.
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 --- Comment #6 from Karen --- Sorry, you right. gcc version 9.2.0 (Homebrew GCC 9.2.0_2) Target: x86_64-apple-darwin19 Configured with: ../configure --build=x86_64-apple-darwin19 --prefix=/usr/local/Cellar/gcc/9.2.0_2 --libdir=/usr/local/Cellar/gcc/9.2.0_2/lib/gcc/9 --disable-nls --enable-checking=release --enable-languages=c,c++,objc,obj-c++,fortran --program-suffix=-9 --with-gmp=/usr/local/opt/gmp --with-mpfr=/usr/local/opt/mpfr --with-mpc=/usr/local/opt/libmpc --with-isl=/usr/local/opt/isl --with-system-zlib --with-pkgversion='Homebrew GCC 9.2.0_2' --with-bugurl=https://github.com/Homebrew/homebrew-core/issues --disable-multilib --with-native-system-header-dir=/usr/include --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 --- Comment #5 from Jonathan Wakely --- (In reply to Karen from comment #4) > Here the additional info: > > GCC version: Apple clang version 11.0.0 (clang-1100.0.33.16) > Target: x86_64-apple-darwin19.2.0 > Configured with: --prefix=/Library/Developer/CommandLineTools/usr > --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/ > usr/include/c++/4.2.1 That confirms you're using OS X, but it's not the compiler you're using. For your case you need to provide the output of 'g++-9 -v' since that's the compiler you're reporting a bug for.
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 --- Comment #4 from Karen --- Here the additional info: GCC version: Apple clang version 11.0.0 (clang-1100.0.33.16) Target: x86_64-apple-darwin19.2.0 Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 --- Comment #3 from Karen --- Created attachment 47723 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47723=edit Testcase preprocessed file
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 --- Comment #2 from Jonathan Wakely --- This is a bug in your libc headers (and I'm guessing you're on OS X). The aligned_alloc function should be declared for C++17 and later, irrespective of the _XOPEN_SOURCE value.
[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |WAITING Last reconfirmed||2020-01-27 Ever confirmed|0 |1 --- Comment #1 from Jonathan Wakely --- Please provide the rest of the info requested by https://gcc.gnu.org/bugs (especially the output of gcc -v)
