On Wed,  4 Aug 2021 11:37:39 +0100
Sergei Trofimovich <slyfox@gentoo.org> wrote:

> In https://gcc.gnu.org/PR101305 gcc introduced ABI-specific
> internal `include` include directory:
> 
> gcc-12:
>   /usr/lib/gcc/x86_64-pc-linux-gnu/12.0.0/32/include
>   /usr/lib/gcc/x86_64-pc-linux-gnu/12.0.0/include
> gcc-11:
>   /usr/lib/gcc/x86_64-pc-linux-gnu/11.2.0/include
> 
> glibc's build system tries to extract only one of them and fails
> the build for 32-bit ABI on x86_64:
> 
>   ../glibc/configure \
>     --prefix=/usr \
>     --build=x86_64-pc-linux-gnu \
>     --host=i686-pc-linux-gnu \
>     --with-headers=/usr/include \
>     CC='x86_64-pc-linux-gnu-gcc -m32' \
>     CXX='x86_64-pc-linux-gnu-g++ -m32' &&
>   make
> 
>   python3 -B ../scripts/gen-as-const.py ...
>   <stdin>:1:10: fatal error: stddef.h: No such file or directory
> 
> To workaround the failure we extend `configure.ac` to also
> lookup `stddef.h` include directory and add it as a lower priority
> search path.
> 
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
>  configure    | 37 ++++++++++++++++++++++++++++++++++---
>  configure.ac | 15 ++++++++++++---
>  2 files changed, 46 insertions(+), 6 deletions(-)
> 
> diff --git a/configure b/configure
> index 9619c10991..cac124f346 100755
> --- a/configure
> +++ b/configure
> @@ -5452,15 +5452,46 @@ $as_echo "$as_me: WARNING:
>  *** some features or tests will be disabled.
>  *** Check the INSTALL file for required versions." >&2;}
>  
> -# if using special system headers, find out the compiler's sekrit
> -# header directory and add that to the list.  NOTE: Only does the right
> -# thing on a system that doesn't need fixincludes.  (Not presently a problem.)
> +# If using special system headers, find out the compiler's internal
> +# header directory and add that to the list to negate -nostdinc effect.
> +# NOTE: Only does the right thing on a system that doesn't need fixincludes.
> +# (Not presently a problem.)
> +# NOTE: sometimes 'include' is also present in gcc's ABI-specific paths
> +# like in https://sourceware.org/PR28183. To avoid it we probe a known
> +# 'stddef.h' header that resides in a common include directory.
>  if test -n "$sysheaders"; then
>    SYSINCLUDES=-nostdinc
>    for d in include include-fixed; do
>      i=`$CC -print-file-name="$d"` && test "x$i" != x && test "x$i" != "x$d" &&
>      SYSINCLUDES="$SYSINCLUDES -isystem $i"
>    done
> +  for f in include/stddef.h; do
> +    i=`$CC -print-file-name="$f"` && test "x$i" != x && test "x$i" != "x$f" &&
> +    d=`$as_dirname -- "$i" ||
> +$as_expr X"$i" : 'X\(.*[^/]\)//*[^/][^/]*/*$' \| \
> +	 X"$i" : 'X\(//\)[^/]' \| \
> +	 X"$i" : 'X\(//\)$' \| \
> +	 X"$i" : 'X\(/\)' \| . 2>/dev/null ||
> +$as_echo X"$i" |
> +    sed '/^X\(.*[^/]\)\/\/*[^/][^/]*\/*$/{
> +	    s//\1/
> +	    q
> +	  }
> +	  /^X\(\/\/\)[^/].*/{
> +	    s//\1/
> +	    q
> +	  }
> +	  /^X\(\/\/\)$/{
> +	    s//\1/
> +	    q
> +	  }
> +	  /^X\(\/\).*/{
> +	    s//\1/
> +	    q
> +	  }
> +	  s/.*/./; q'` &&
> +    SYSINCLUDES="$SYSINCLUDES -isystem $d"
> +  done
>    SYSINCLUDES="$SYSINCLUDES \
>  -isystem `echo $sysheaders | sed 's/:/ -isystem /g'`"
>    if test -n "$CXX"; then
> diff --git a/configure.ac b/configure.ac
> index 34ecbba540..9507a552ff 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1083,15 +1083,24 @@ test -n "$aux_missing" && AC_MSG_WARN([
>  *** some features or tests will be disabled.
>  *** Check the INSTALL file for required versions.])
>  
> -# if using special system headers, find out the compiler's sekrit
> -# header directory and add that to the list.  NOTE: Only does the right
> -# thing on a system that doesn't need fixincludes.  (Not presently a problem.)
> +# If using special system headers, find out the compiler's internal
> +# header directory and add that to the list to negate -nostdinc effect.
> +# NOTE: Only does the right thing on a system that doesn't need fixincludes.
> +# (Not presently a problem.)
> +# NOTE: sometimes 'include' is also present in gcc's ABI-specific paths
> +# like in https://sourceware.org/PR28183. To avoid it we probe a known
> +# 'stddef.h' header that resides in a common include directory.
>  if test -n "$sysheaders"; then
>    SYSINCLUDES=-nostdinc
>    for d in include include-fixed; do
>      i=`$CC -print-file-name="$d"` && test "x$i" != x && test "x$i" != "x$d" &&
>      SYSINCLUDES="$SYSINCLUDES -isystem $i"
>    done
> +  for f in include/stddef.h; do
> +    i=`$CC -print-file-name="$f"` && test "x$i" != x && test "x$i" != "x$f" &&
> +    d=`AS_DIRNAME(["$i"])` &&
> +    SYSINCLUDES="$SYSINCLUDES -isystem $d"
> +  done
>    SYSINCLUDES="$SYSINCLUDES \
>  -isystem `echo $sysheaders | sed 's/:/ -isystem /g'`"
>    if test -n "$CXX"; then

Does approach look reasonable?

-- 

  Sergei