Re: Fix gcc bootstrap problem

[Michael Matz <matz at suse dot de>]

Hi Nick,

[full quote for Richard]

On Mon, 20 Aug 2007, Nick Clifton wrote:

> Hi Guys,
> 
>   I ran a x86 hosted bootstrap of the mainline gcc and binutils
>   sources over the weekend and it failed with this error report:
> 
>     bfd/elflink.c: In function 'elf_fixup_link_order':
>     bfd/elflink.c:9893: error: type mismatch in unary expression
>     long unsigned int
>     int
>     D.16764 = -D.16763

This and the error below are really compiler bugs (frontend missing to 
generate appropriate casts), which the type verifier now catches, i.e. 
internal compiler errors.  Please create a bug report or provide a 
preprocessed file showing the problem.

>   Not exactly the most helpful error report in the world, but with a
>   set of tree dumps and a bit of guesswork I tracked the problem down
>   to this line:
> 
>     offset &= ~(bfd_vma)((1 << s->alignment_power) - 1);
> 
>   Gcc has worked out that "~ foo - 1" is the same as "- foo" but it
>   has failed to appreciate that the (bfd_vma) cast should apply to the
>   constant 1 as well as the expression (1 << s->alignment_power).  So
>   it thinks that the expression above is equivalent to (paraphrasing
>   slightly....): 
> 
>     unsigned long int D.16764;
>     signed int D.16763;
> 
>     D.16763 = 1 << s->alignment_power;
>     D.16764 = - D.16763;
> 
>     offset = offset & D.16764;
> 
>   Hence it is complaining about the unary conversion of D.16763 into
>   D.16764.  I think that this is probably a gimplification bug but
>   that is beyond me, so I have Cc'ed this email to the gcc bugs list.
>   In the meantime however I have hit on a simple workaround:
>   
>     offset &= (bfd_vma)~((1 << s->alignment_power) - 1);
> 
>   (ie moving the cast to a (bfd_vma) to before the inversion
>   operator).  This works in the bootstrap although it would fail if
>   the alignment power is sufficiently large to cause the left shift to
>   overflow an integer.  So I am going to check in a variant of this
>   change:
> 
>     offset &= (bfd_vma)~((1L << s->alignment_power) - 1L);
> 
>   which I think should satisfy everyone.  I will also check the patch
>   into the 2.18 branch.
> 
> Cheers
>   Nick
> 
> PS.  The bootstrap still does not succeed with this patch
>   installed.  It fails later on with this error report:
> 
>   i386-dis.c:4213: error: type mismatch in pointer plus expression
>     struct dis386 *
>     struct dis386[8] *
>     unsigned int 
>     dp = &float_reg + D.7721
> 
>   I am looking into this now.
>   
> bfd/ChangeLog
> 2007-08-20  Nick Clifton  <nickc@redhat.com>
> 
> 	* elflink.c (elf_fixup_link_order): Rewrite conversion of
> 	s->alignment_power into an offset mask in order to avoid a gcc
> 	error message.
> 
> Index: bfd/elflink.c
> ===================================================================
> RCS file: /cvs/cvsfiles/devo/bfd/elflink.c,v
> retrieving revision 1.95
> diff -c -3 -p -r1.95 elflink.c
> *** bfd/elflink.c	19 Aug 2007 17:49:44 -0000	1.95
> --- bfd/elflink.c	20 Aug 2007 07:39:30 -0000
> *************** elf_fixup_link_order (bfd *abfd, asectio
> *** 9965,9971 ****
>     for (n = 0; n < seen_linkorder; n++)
>       {
>         s = sections[n]->u.indirect.section;
> !       offset &= ~(bfd_vma)((1 << s->alignment_power) - 1);
>         s->output_offset = offset;
>         sections[n]->offset = offset;
>         offset += sections[n]->size;
> --- 9965,9971 ----
>     for (n = 0; n < seen_linkorder; n++)
>       {
>         s = sections[n]->u.indirect.section;
> !       offset &= (bfd_vma)~((1L << s->alignment_power) - 1L);
>         s->output_offset = offset;
>         sections[n]->offset = offset;
>         offset += sections[n]->size;
>