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[Xen-devel] Allow compile with CONFIG_DEBUG_INFO=y, X86_PAE not set on g

To: linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Allow compile with CONFIG_DEBUG_INFO=y, X86_PAE not set on gcc 3.4.5
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Fri, 8 Aug 2008 15:04:33 +1000
Cc: Mark McLoughlin <markmc@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, Stephen Tweedie <sct@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Dhaval Giani <dhaval@xxxxxxxxxxxxxxxxxx>
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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.

        arch/x86/mm/pgtable.c: In function `pgd_prepopulate_pmd':
        arch/x86/mm/pgtable.c:222: internal compiler error: in remove_insn, at 
        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

        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>

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 
+++ 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)
-#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 
+{ }
+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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