[binutils-gdb] gdbsupport: include cstdlib in common-defs.h

[binutils-gdb] gdbsupport: include cstdlib in common-defs.h

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ff8885c3be6f42ed90a7b0ec0028fad26861cd94

commit ff8885c3be6f42ed90a7b0ec0028fad26861cd94
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Mon Apr 27 09:19:48 2020 -0400

    gdbsupport: include cstdlib in common-defs.h
    
    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.

Diff:
---
 gdbsupport/ChangeLog     | 4 ++++
 gdbsupport/common-defs.h | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/gdbsupport/ChangeLog b/gdbsupport/ChangeLog
index 78fbbe65c70..b071049ae73 100644
--- a/gdbsupport/ChangeLog
+++ b/gdbsupport/ChangeLog
@@ -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.
diff --git a/gdbsupport/common-defs.h b/gdbsupport/common-defs.h
index e42d2b80c04..d3f5eafa455 100644
--- a/gdbsupport/common-defs.h
+++ b/gdbsupport/common-defs.h
@@ -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>