bug#36882: Qemu 4.2.0 build for x86_64-linux fails

["Ludovic Courtès" <ludo@gnu.org>]

Hi Mathieu,

Mathieu Othacehe <m.othacehe@gmail.com> skribis:

> On master, when building qemu, this is the gcc include path (obtained
> with "gcc -v -x c -E /dev/null"):
>
>  /gnu/store/adm2cx3ayabn1sp84nnjsk0672m800ip-flex-2.6.4/include
>  /gnu/store/l86azr7r3p5631wj3kk329jl1y1mpjgy-bzip2-1.0.6/include
>  ...
>  /gnu/store/2plcy91lypnbbysb18ymnhaw3zwk8pg1-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/include [1]
>  /gnu/store/2plcy91lypnbbysb18ymnhaw3zwk8pg1-gcc-7.4.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.4.0/include-fixed
>  /gnu/store/ahqgl4h89xqj695lgqvsaf6zh2nhy4pj-glibc-2.29/include [2]
>
>
> We see that glibc comes last. So when building a program with "gcc
> -ffreestanding -m16", the first <stdint.h> header picked is the one from
> gcc (marked [1] above). This header contains:
>
> #ifndef _GCC_WRAP_STDINT_H
>   #if __STDC_HOSTED__ <-- Set to 0 because of -ffreestanding option.
>     # if defined __cplusplus && __cplusplus >= 201103L
>       #  undef __STDC_LIMIT_MACROS
>       #  define __STDC_LIMIT_MACROS
>       #  undef __STDC_CONSTANT_MACROS
>       #  define __STDC_CONSTANT_MACROS
>     # endif
>     # include_next <stdint.h>
>   #else
>     # include "stdint-gcc.h" <-- This one gets included.
>   #endif
>   #define _GCC_WRAP_STDINT_H
> #endif
>
>
> So the <stdint.h> from glibc (marked [2] above) is neved included. And
> that's good because this header would try to include <gnu/stubs-32.h>
> that our glibc does not provide.

[...]

> Now, what's happening on core-updates? Because of CPATH ->
> C_INCLUDE_PATH transition, we have a different behaviour. The same
> command as above states:
>
> ignoring duplicate directory "/gnu/store/jsjsczgr8xdnbdminl7lm2v56b7dq7lq-glibc-2.31/include"
> ...
>  /gnu/store/kyypmcn2miyzllqqmcx28gvj89qnvhpi-flex-2.6.4/include
>  ...
>  /gnu/store/jsjsczgr8xdnbdminl7lm2v56b7dq7lq-glibc-2.31/include [1]
>  ...
>  /gnu/store/wl7zanqf0s9bfppggmv8qxqan71fjfw8-gcc-7.5.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.5.0/include [2]
>  /gnu/store/wl7zanqf0s9bfppggmv8qxqan71fjfw8-gcc-7.5.0-lib/lib/gcc/x86_64-unknown-linux-gnu/7.5.0/include-fixed
>
> The glibc ignored seems to be the hardcoded one. The one from the
> C_INCLUDE_PATH is kept. So the <stdint.h> included is the one from glibc
> (marked [1] above), which triggers <gnu/stubs-32.h> inclusion and makes
> build fail.

Woow, thanks for the analysis.

It’s a bug on ‘core-updates’ that GCC’s headers come after libc’s.  This
is what should be fixed IMO.

So is it expected that C_INCLUDE_PATH comes before the hard-coded GCC
include directory?  How can we work around that?

Thanks!

Ludo’.