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When _XOPEN_SOURCE is set,<cstdlib> and <ctime> started to fail on macOS, missing ::aligned_alloc and ::timespec_get #46552

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stbergmann opened this issue Aug 17, 2020 · 8 comments
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When _XOPEN_SOURCE is set,<cstdlib> and <ctime> started to fail on macOS, missing ::aligned_alloc and ::timespec_get #46552

stbergmann opened this issue Aug 17, 2020 · 8 comments
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@ldionne
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bugzilla Issues migrated from bugzilla libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.

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@stbergmann
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Bugzilla Link 47208
Resolution FIXED
Resolved on Sep 02, 2020 09:23
Version unspecified
OS Linux
CC @ldionne,@mclow
Fixed by commit(s) 5201b96

Extended Description

On macOS, with recent LLVM 12 trunk commit 67dfba9 " [libc++] Provide std::aligned_alloc and std::timespec_get on Apple platforms":

$ cat test.cc
#include
#include

$ .../llvm/inst/bin/clang++ -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -std=c++17 -fsyntax-only test.cc

$ .../llvm/inst/bin/clang++ -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -std=c++17 -fsyntax-only test.cc -D_XOPEN_SOURCE=600
In file included from test.cc:1:
.../llvm/inst/bin/../include/c++/v1/cstdlib:158:9: error: no member named 'aligned_alloc' in the global namespace
using ::aligned_alloc;
~~^
In file included from test.cc:2:
.../llvm/inst/bin/../include/c++/v1/ctime:76:9: error: no member named 'timespec_get' in the global namespace; did you mean 'timespec'?
using ::timespec_get;
~~^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include/sys/_types/_timespec.h:33:1: note: 'timespec' declared here
_STRUCT_TIMESPEC
^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include/sys/_types/_timespec.h:29:40: note: expanded from macro '_STRUCT_TIMESPEC'
#define _STRUCT_TIMESPEC struct timespec
^
2 errors generated.

...and similarly for other values of _XOPEN_SOURCE, like 700. I noticed that when building ICU 67.1 as part of building recent master LibreOffice, where some place in the ICU sources sets _XOPEN_SOURCE to 600.

  • One approach to fix this would be to make the condition in libcxx match the condition in Apple's SDK headers, with something like

diff --git a/libcxx/include/__config b/libcxx/include/__config
index d7b6a2acaef..fb5ca54493b 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -327,6 +327,10 @@

define _LIBCPP_USING_DEV_RANDOM

#endif

+#if defined(APPLE)
+# include <sys/cdefs.h>
+#endif
+
#if !defined(_LIBCPP_LITTLE_ENDIAN) && !defined(_LIBCPP_BIG_ENDIAN)

include <endian.h>

if __BYTE_ORDER == __LITTLE_ENDIAN

@@ -383,7 +387,8 @@

elif defined(APPLE)

  // timespec_get and aligned_alloc were introduced in macOS 10.15 and
  // aligned releases

-# if (ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED >= 101500 ||
+# if __DARWIN_C_LEVEL >= __DARWIN_C_FULL && \

  •    (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101500 || \
    __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ >= 130000 || \
    __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ >= 130000 || \
    __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ >= 60000)

  • Another approach could be to change Apple's SDK headers, so that for C++ ::aligned_alloc and ::timespec_get would get declared regardless of any _XOPEN_SOURCE?

  • And yet another approach could be to declare that _XOPEN_SOURCE must not be defined when compiling C++ source (after all, at least technically it is an identifier that is reserved to the implementation), and instead fix ICU.

Thoughts how to proceed?
@stbergmann
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assigned to @ldionne

@ldionne
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ldionne commented Sep 1, 2020

Thanks a lot for the heads up and the analysis, Stephan.

My inclination would be that the SDK headers should provide those declarations regardless of _XOPEN_SOURCE, since otherwise it looks like the implementation is not a valid C99 implementation when _XOPEN_SOURCE is defined. For the sake of keeping things simple, I like to push towards libc++ requiring a valid C99 implementation under it in order to work.

I'll ask the libc folks here at Apple what they think -- I'm sure there's a reason for the _XOPEN_SOURCE dance in the SDK.

@ldionne
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ldionne commented Sep 1, 2020

So, actually, in the latest SDK, the condition for aligned_alloc is:

#if (__DARWIN_C_LEVEL >= __DARWIN_C_FULL) || \
    (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) || \
    (defined(__cplusplus) && __cplusplus >= 201703L)
void    *aligned_alloc(size_t __alignment, size_t __size);
#endif

But for timespec_get it's still:

#if (__DARWIN_C_LEVEL >= __DARWIN_C_FULL) && \
        ((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) || \
        (defined(__cplusplus) && __cplusplus >= 201703L))
int timespec_get(struct timespec *ts, int base);
#endif

So it looks like it was meant to be fixed, since they fixed in for aligned_alloc. I'll report the issue for timespec_get.

In the meantime, it does look like we should add a #if __DARWIN_C_LEVEL >= __DARWIN_C_FULL guard to whether libc++ provides the declarations.

@ldionne
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ldionne commented Sep 1, 2020

I just committed a fix:

commit 99f3b23
Author: Louis Dionne ldionne@apple.com
Date: Tue Sep 1 15:05:33 2020 -0400

[libc++] Workaround timespec_get not always being available in Apple SDKs

timespec_get is not available in Apple SDKs when (__DARWIN_C_LEVEL >= __DARWIN_C_FULL)
isn't true, which leads to libc++ trying to import ::timespec_get into
namespace std when it's not available. This issue has been reported to
Apple's libc, but we need a workaround in the meantime.

llvm/llvm-project#46552 
rdar://68157284

Can you please let me know if it fixes your issue? It does fix the reproducer I created locally (and checked into the test suite).

@ldionne
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ldionne commented Sep 1, 2020

Note that my commit only tackles timespec_get, since aligned_alloc has been fixed already. What SDK are you using?

@stbergmann
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Note that my commit only tackles timespec_get, since aligned_alloc has been
fixed already. What SDK are you using?

I'm using /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk from Xcode Version 11.6 (11E708), which appears to be the latest one publicly available?

@stbergmann
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Note that my commit only tackles timespec_get, since aligned_alloc has been
fixed already. What SDK are you using?

I'm using
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/
Developer/SDKs/MacOSX10.15.sdk from Xcode Version 11.6 (11E708), which
appears to be the latest one publicly available?

Found Xcode 12 beta 6 now, which has the updated MacOSX11.0.sdk/usr/include/malloc/_malloc.h, and with which my original issue is indeed fixed. Thanks!

@ldionne
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ldionne commented Sep 2, 2020

Note that 99f3b23 was reverted because it broke the modules build, but I just checked-in this commit which should fix the bug without breaking modules:

commit 5201b96
Author: Louis Dionne ldionne@apple.com
Date: Wed Sep 2 10:36:48 2020 -0400

[libc++] Re-apply the workaround for timespec_get not always being available in Apple SDKs

This commit re-applies 99f3b231cb21, which was reverted in 814242572731
because it broke the modules build. The modules failure was a circular
dependency between the Darwin module and __config. Specifically, the
issue was that if <__config> includes a system header, the std_config
module depends on the Darwin module. However, the Darwin module already
depends on the std_config header because some of its headers include
libc++ headers like <ctype.h> (they mean to include the C <ctype.h>,
but libc++ headers are first in the header search path).

This is fixed by moving the workaround to <ctime> only.

llvm/llvm-project#46552 
rdar://68157284

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
This issue was closed.
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