[Xen-devel] Re: Allow compile with CONFIG_DEBUG_INFO=y, X86_PAE not set on gcc 3.4.5

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Simon Horman wrote:
> Hi,
>
> It appears that "x86: preallocate and prepopulate separately"
> (d8d5900ef8afc562088f8470feeaf17c4747790f) introduced a minor regression.
> The build fails on gcc 3.4.5 if CONFIG_DEBUG_INFO=y (that is gcc is
> called with -g) and X86_PAE not set.
>
> There was previously some discussion of this without resolution.
> http://lkml.org/lkml/2008/7/18/250
>
>         arch/x86/mm/pgtable.c: In function `pgd_prepopulate_pmd':
>         arch/x86/mm/pgtable.c:222: internal compiler error: in remove_insn, at 
> emit-rtl.c:3746
>         Please submit a full bug report,
>         with preprocessed source if appropriate.
>         See <URL:http://gcc.gnu.org/bugs.html> for instructions.
>
>         # i686-unknown-linux-gnu-gcc --version
>         i686-unknown-linux-gnu-gcc (GCC) 3.4.5
>
> My investigations seem to show that gcc 3.4.5 can't cope with the following
> construct:
>
>         for (i = 0; i < 0; i++)
>                 ...
>
> or more specifically:
>
>         for (i = 0; i < PREALLOCTED_PMDS; i++)
>                 ...
>
> when PREALLOCTED_PMDS is 0. That is, when X86_PAE is not set.
>
> This patch resolves this problem by moving the relevant code inside
> #define X86_PAE and providing dummy functions outside !X86_PAE.
>
> Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
>   
We resolved the other report by saying that gcc 3.4.4 is broken. It 
seems 3.4.5 is as well.  Could you just update the compiler?  I'd rather 
not have to clutter the code with more ifdefs if we can possibly avoid it.
Does putting

        if (PREALLOCATED_PMDS == 0)
                return;


before the for loop help?

   J

> Index: linux-2.6/arch/x86/mm/pgtable.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/pgtable.c        2008-08-08 14:35:29.000000000 
> +1000
> +++ linux-2.6/arch/x86/mm/pgtable.c     2008-08-08 15:00:07.000000000 +1000
> @@ -141,12 +141,6 @@ void pud_populate(struct mm_struct *mm, 
>  	if (mm == current->active_mm)
>                 write_cr3(read_cr3());
>  }
> -#else  /* !CONFIG_X86_PAE */
> -
> -/* No need to prepopulate any pagetable entries in non-PAE modes. */
> -#define PREALLOCATED_PMDS      0
> -
> -#endif /* CONFIG_X86_PAE */
>  
>  static void free_pmds(pmd_t *pmds[])
>  {
> @@ -221,6 +215,19 @@ static void pgd_prepopulate_pmd(struct m
>         }
>  }
>  
> +#else  /* !CONFIG_X86_PAE */
> +
> +/* No need to prepopulate any pagetable entries in non-PAE modes. */
> +#define PREALLOCATED_PMDS      0
> +
> +static int preallocate_pmds(pmd_t *pmds[]) { return 0; }
> +static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t 
> *pmds[])
> +{ }
> +static void free_pmds(pmd_t *pmds[]) { }
> +static void pgd_mop_up_pmds(struct mm_struct *mm, pgd_t *pgdp) { }
> +
> +#endif /* CONFIG_X86_PAE */
> +
>  pgd_t *pgd_alloc(struct mm_struct *mm)
>  {
>         pgd_t *pgd;
>   
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