Re: [PATCH] disas/libvixl: Protect C system header for C++ compiler

[Philippe Mathieu-Daudé]

Forgot to tag as RFC.

Cc'ing mjt to have feedback from Debian packaging.

On 5/15/21 8:35 PM, Philippe Mathieu-Daudé wrote:
> When selecting an ARM target on Debian unstable, we get:
> 
>   Compiling C++ object libcommon.fa.p/disas_libvixl_vixl_utils.cc.o
>   FAILED: libcommon.fa.p/disas_libvixl_vixl_utils.cc.o
>   c++ -Ilibcommon.fa.p -I. -I.. [...] -o 
> libcommon.fa.p/disas_libvixl_vixl_utils.cc.o -c ../disas/libvixl/vixl/utils.cc
>   In file included from /home/philmd/qemu/disas/libvixl/vixl/utils.h:30,
>                    from ../disas/libvixl/vixl/utils.cc:27:
>   /usr/include/string.h:36:43: error: missing binary operator before token "("
>      36 | #if defined __cplusplus && (__GNUC_PREREQ (4, 4) \
>         |                                           ^
>   /usr/include/string.h:53:62: error: missing binary operator before token "("
>      53 | #if defined __USE_MISC || defined __USE_XOPEN || __GLIBC_USE 
> (ISOC2X)
>         |                                                              ^
>   /usr/include/string.h:165:21: error: missing binary operator before token 
> "("
>     165 |      || __GLIBC_USE (LIB_EXT2) || __GLIBC_USE (ISOC2X))
>         |                     ^
>   /usr/include/string.h:174:43: error: missing binary operator before token 
> "("
>     174 | #if defined __USE_XOPEN2K8 || __GLIBC_USE (LIB_EXT2) || __GLIBC_USE 
> (ISOC2X)
>         |                                           ^
>   /usr/include/string.h:492:19: error: missing binary operator before token 
> "("
>     492 | #if __GNUC_PREREQ (3,4)
>         |                   ^
> 
> Similarly to commit 875df03b221 ('osdep: protect qemu/osdep.h with
> extern "C"'), guard the <string.h> system header with 'extern "C"'.
> 
> Relevant information from the host:
> 
>   $ lsb_release -d
>   Description:    Debian GNU/Linux 11 (bullseye)
>   $ gcc --version
>   gcc (Debian 10.2.1-6) 10.2.1 20210110
>   $ dpkg -S /usr/include/string.h
>   libc6-dev: /usr/include/string.h
>   $ apt-cache show libc6-dev
>   Package: libc6-dev
>   Version: 2.31-11
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1914870
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> RFC because I've no idea about C++, but this fixes the build for me.
> 
> Quick reproducer:
> 
>   $ ../configure --disable-tools --target-list=aarch64-linux-user
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Thomas Huth <thuth@redhat.com>
> ---
>  disas/libvixl/vixl/utils.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/disas/libvixl/vixl/utils.h b/disas/libvixl/vixl/utils.h
> index 5ab134e240a..fc28d7456c1 100644
> --- a/disas/libvixl/vixl/utils.h
> +++ b/disas/libvixl/vixl/utils.h
> @@ -27,8 +27,10 @@
>  #ifndef VIXL_UTILS_H
>  #define VIXL_UTILS_H
>  
> -#include <string.h>
>  #include <cmath>
> +extern "C" {
> +#include <string.h>
> +}
>  #include "vixl/globals.h"
>  #include "vixl/compiler-intrinsics.h"
>  
>