Bug#1069066: LIMITS_H_TEST is frequently wrong on Debian

[Helmut Grohne <helmut@subdivi.de>]

Source: gcc-14
Tags: patch upstream
Forwarded: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80677
User: helmutg@debian.org
Usertags: rebootstrap
X-Debbugs-Cc: debian-cross@lists.debian.org

Hi Matthias,

I've been fighting LIMITS_H_TEST for a long time. The basic problem with
it is that it uses different search paths from the actual compiler and
thus ends up occasionally detecting absence of limits.h when limits.h
really does exist. There have been various attempts to rectify this and
most of them are documented in the forwarded gcc ticket. Ultimately
though, I think the best course of action is deferring the check from a
build-time check to a run-time check thus using the actual compiler's
search path removing any possibility for misdetection. This can be done
using has_include_next in principle, but until recently,
has_include_next was broken on gcc in ways that would make this solution
inapplicable. These problems with has_include_next have recently been
resolved in gcc-14 and the Debian package includes a working version. As
a result I suggest that we also move forward with my proposed
LIMITS_H_TEST replacement in Debian. Upstream gcc fails to move forward
here and the problem affects Debian in particular due to our use of
multiarch and our changing of the compiler search path. Would you agree
to carry this as a Debian patch until gcc manages to fix it one way or
another? I've been using this last iteration of the patch for quite a
while now and didn't have any misdetections since.

Helmut

--- a/src/gcc/limitx.h
+++ b/src/gcc/limitx.h
@@ -29,7 +29,7 @@
 #ifndef _GCC_LIMITS_H_  /* Terminated in limity.h.  */
 #define _GCC_LIMITS_H_

-#ifndef _LIBC_LIMITS_H_
+#if !defined(_LIBC_LIMITS_H_) && __has_include_next(<limits.h>)
 /* Use "..." so that we find syslimits.h only in this same directory.  */
 #include "syslimits.h"
 #endif
--- a/src/gcc/limity.h
+++ b/src/gcc/limity.h
@@ -3,7 +3,7 @@

 #else /* not _GCC_LIMITS_H_ */

-#ifdef _GCC_NEXT_LIMITS_H
+#if defined(_GCC_NEXT_LIMITS_H) && __has_include_next(<limits.h>)
 #include_next <limits.h>		/* recurse down to the real one */
 #endif

--- a/src/gcc/Makefile.in
+++ b/src/gcc/Makefile.in
@@ -3139,11 +3139,7 @@
 	  sysroot_headers_suffix=`echo $${ml} | sed -e 's/;.*$$//'`; \
 	  multi_dir=`echo $${ml} | sed -e 's/^[^;]*;//'`; \
	  include_dir=include$${multi_dir}; \
-	  if $(LIMITS_H_TEST) ; then \
-	    cat $(srcdir)/limitx.h $(T_GLIMITS_H) $(srcdir)/limity.h > tmp-xlimits.h; \
-	  else \
-	    cat $(T_GLIMITS_H) > tmp-xlimits.h; \
-	  fi; \
+	  cat $(srcdir)/limitx.h $(T_GLIMITS_H) $(srcdir)/limity.h > tmp-xlimits.h; \
	  $(mkinstalldirs) $${include_dir}; \
	  chmod a+rx $${include_dir} || true; \
 	  $(SHELL) $(srcdir)/../move-if-change \