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

[Thomas Huth]

On 15/05/2021 20.35, 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>
> +}

Could you please try to backport the upstream patch instead:

https://git.linaro.org/arm/vixl.git/commit/?id=78973f258039f6e96

See the changes to utils-vixl.h:

diff --git a/src/utils-vixl.h b/src/utils-vixl.h
index 06c7551e..b27310db 100644
--- a/src/utils-vixl.h
+++ b/src/utils-vixl.h
@@ -27,9 +27,8 @@
 #ifndef VIXL_UTILS_H
 #define VIXL_UTILS_H

-#include <string.h>
-
 #include <cmath>
+#include <cstring>
 #include <vector>

 #include "compiler-intrinsics-vixl.h"

 Thomas