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gdbsupport: include cstdlib in common-defs.h

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In PR 25731 [1], the following build failure was reported:

    ../../binutils-gdb/gdb/gdbtypes.c:1254:10: error: no member named 'abs' in namespace 'std'; did you mean simply 'abs'?
                = ((std::abs (stride) * element_count) + 7) / 8;
                    ^~~~~~~~
                    abs
    /usr/include/stdlib.h:129:6: note: 'abs' declared here
    int      abs(int) __pure2;
             ^
The original report was using:

    $ gcc -v
    Apple LLVM version 8.0.0 (clang-800.0.42.1)
    Target: x86_64-apple-darwin15.6.0

Note that I was _not_ able to reproduce using:

    $ g++ --version
    Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
    Apple clang version 11.0.0 (clang-1100.0.33.17)
    Target: x86_64-apple-darwin19.3.0

The proposed fix is to include <cstdlib> in addition to <stdlib.h>.

Here's an excerpt of [2] relevant to this problem:

    These headers [speaking of the .h form] are allowed to also declare
    the same names in the std namespace, and the corresponding cxxx
    headers are allowed to also declare the same names in the global
    namespace: including <cstdlib> definitely provides std::malloc and
    may also provide ::malloc.  Including <stdlib.h> definitely provides
    ::malloc and may also provide std::malloc

Since we use std::abs, we should not assume that our include of stdlib.h
declares an `abs` function in the `std` namespace.

If we replace the include of stdlib.h with cstdlib, then we fall in the
opposite situation.  A standard C++ library may decide to only put the
declarations in the std namespace, requiring us to prefix all standard
functions with `std::`.  I'm not against that, but for the moment I think the
safest way forward is to just include both.

Note that I don't know what effect this patch can have on any stdlib.h fix
provided by gnulib.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=25731
[2] https://en.cppreference.com/w/cpp/header#C_compatibility_headers

gdbsupport/ChangeLog:

	* common-defs.h: Include cstdlib.h.
This commit is contained in:
Simon Marchi 2020-04-27 09:19:48 -04:00 • committed by Simon Marchi
parent 991a3e2e99
commit ff8885c3be
2 changed files with 9 additions and 0 deletions
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4
gdbsupport/ChangeLog
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@ -1,3 +1,7 @@
2020-04-27 Simon Marchi <simon.marchi@polymtl.ca>
* common-defs.h: Include cstdlib.h.
2020-04-20 Tom Tromey <tromey@adacore.com>
* scoped_mmap.h (scoped_mmap): Mark move constructor as noexcept.

5
gdbsupport/common-defs.h
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@ -84,7 +84,12 @@
#include <stdarg.h>
#include <stdio.h>
/* Include both cstdlib and stdlib.h to ensure we have standard functions
defined both in the std:: namespace and in the global namespace. */
#include <cstdlib>
#include <stdlib.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>