gdbsupport: include cstdlib in common-defs.h

Message ID 20200409225022.3093099-1-simon.marchi@polymtl.ca
State New
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  • gdbsupport: include cstdlib in common-defs.h
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Commit Message

Keith Seitz via Gdb-patches April 9, 2020, 10:50 p.m.
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.
---
 gdbsupport/common-defs.h | 1 +
 1 file changed, 1 insertion(+)

-- 
2.26.0

Comments

Keith Seitz via Gdb-patches April 9, 2020, 11:34 p.m. | #1
On Thu, Apr 9, 2020 at 5:50 PM Simon Marchi via Gdb-patches
<gdb-patches@sourceware.org> wrote:
>

> 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.

> ---

>  gdbsupport/common-defs.h | 1 +

>  1 file changed, 1 insertion(+)

>

> diff --git a/gdbsupport/common-defs.h b/gdbsupport/common-defs.h

> index e42d2b80c045..257b6279b888 100644

> --- a/gdbsupport/common-defs.h

> +++ b/gdbsupport/common-defs.h

> @@ -84,6 +84,7 @@

>

>  #include <stdarg.h>

>  #include <stdio.h>

> +#include <cstdlib>

>  #include <stdlib.h>

>  #include <stddef.h>

>  #include <stdint.h>


I think this is reasonable, but I would add a comment why both cstdlib
and stdlib.h are included (ie. to get the std:: version with
overloaded functions)

Christian
Keith Seitz via Gdb-patches April 10, 2020, 2:39 p.m. | #2
On 2020-04-09 7:34 p.m., Christian Biesinger wrote:
> I think this is reasonable, but I would add a comment why both cstdlib

> and stdlib.h are included (ie. to get the std:: version with

> overloaded functions)


A comment would certainly be useful.  Does that sound right?

/* Include both stdlib.h and cstdlib to make sure to get the standard C
   functions in the global namespace and the overloads in the std
   namespace.  */

Simon
Keith Seitz via Gdb-patches April 10, 2020, 5:29 p.m. | #3
On Fri, Apr 10, 2020 at 9:40 AM Simon Marchi <simon.marchi@polymtl.ca> wrote:
>

> On 2020-04-09 7:34 p.m., Christian Biesinger wrote:

> > I think this is reasonable, but I would add a comment why both cstdlib

> > and stdlib.h are included (ie. to get the std:: version with

> > overloaded functions)

>

> A comment would certainly be useful.  Does that sound right?

>

> /* Include both stdlib.h and cstdlib to make sure to get the standard C

>    functions in the global namespace and the overloads in the std

>    namespace.  */


That sounds good to me.
Keith Seitz via Gdb-patches April 27, 2020, 1:30 p.m. | #4
On 2020-04-10 1:29 p.m., Christian Biesinger wrote:
> On Fri, Apr 10, 2020 at 9:40 AM Simon Marchi <simon.marchi@polymtl.ca> wrote:

>>

>> On 2020-04-09 7:34 p.m., Christian Biesinger wrote:

>>> I think this is reasonable, but I would add a comment why both cstdlib

>>> and stdlib.h are included (ie. to get the std:: version with

>>> overloaded functions)

>>

>> A comment would certainly be useful.  Does that sound right?

>>

>> /* Include both stdlib.h and cstdlib to make sure to get the standard C

>>    functions in the global namespace and the overloads in the std

>>    namespace.  */

> 

> That sounds good to me.

> 


I pushed this patch, although with a slightly different comment, because I forgot
I had written one here.  But it says essentially the same thing.

Simon

Patch

diff --git a/gdbsupport/common-defs.h b/gdbsupport/common-defs.h
index e42d2b80c045..257b6279b888 100644
--- a/gdbsupport/common-defs.h
+++ b/gdbsupport/common-defs.h
@@ -84,6 +84,7 @@ 
 
 #include <stdarg.h>
 #include <stdio.h>
+#include <cstdlib>
 #include <stdlib.h>
 #include <stddef.h>
 #include <stdint.h>