Re: [Xen-ia64-devel] Mini-OS registers and libgcc

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>]

Hello,

Dietmar Hahn, le Wed 13 Feb 2008 11:53:59 +0100, a écrit :
> Am Dienstag, 12. Februar 2008 schrieb Samuel Thibault:
> > Is there a reason for using -mfixed-range=f2-f5,f12-f15,f32-f127
> > when compiling Mini-OS?  Is it really needed since it doesn't
> > have a user-land? (though I guess some support would be needed in
> > switch_context for instance)
> 
> To handle this in a clean way the trap_frame has to be expanded and some fp 
> registers have to stored/restored in trap handling.

Ok. Would this be needed in order to be able to use libgcc.a?

> > Then, are there other reasons for using __*div/di*.S instead of just
> > linking with libgcc?
> 
> It's possible to use libgcc.a but the flag -mconstant-gp has to be removed 
> from the mini-os makefiles and a clean way to add libgcc.a is needed.

Something like the attached patch?

Actually I'm asking because for other purpose, I would need __divdi on
x86_32, and using libgcc.a is a really simple solution.

> By the way current mini-os crashed with Unaligned Reference. 
> A small change is needed:
>  static void maybe_split(struct xmalloc_hdr *hdr, size_t size, size_t block)
>  {
>      struct xmalloc_hdr *extra;
> -    size_t leftover = block - size;
> +    size_t leftover;
> +#if defined(__ia64__)
> +    size = (size +7 ) & ~7;  /* alignment needed on 8 byte boundary. */
> +#endif
> +    leftover = block - size;

Does the following patch work?

diff -r 3cc84775d725 extras/mini-os/lib/xmalloc.c
--- a/extras/mini-os/lib/xmalloc.c      Tue Feb 12 17:04:32 2008 +0000
+++ b/extras/mini-os/lib/xmalloc.c      Wed Feb 13 12:03:52 2008 +0000
@@ -62,10 +62,19 @@ struct xmalloc_pad
     size_t hdr_size;
 };
 
+/* Return size, increased to alignment with align. */
+static inline size_t align_up(size_t size, size_t align)
+{
+    return (size + align - 1) & ~(align - 1);
+}
+
 static void maybe_split(struct xmalloc_hdr *hdr, size_t size, size_t block)
 {
     struct xmalloc_hdr *extra;
-    size_t leftover = block - size;
+    size_t leftover;
+    size = align_up(size, __alignof__(struct xmalloc_hdr));
+    size = align_up(size, __alignof__(struct xmalloc_pad));
+    leftover = block - size;
 
     /* If enough is left to make a block, put it on free list. */
     if ( leftover >= (2 * (sizeof(struct xmalloc_hdr) + sizeof(struct 
xmalloc_pad))) )
@@ -98,12 +107,6 @@ static struct xmalloc_hdr *xmalloc_new_p
     maybe_split(hdr, size, PAGE_SIZE);
 
     return hdr;
-}
-
-/* Return size, increased to alignment with align. */
-static inline size_t align_up(size_t size, size_t align)
-{
-    return (size + align - 1) & ~(align - 1);
 }
 
 /* Big object?  Just use the page allocator. */

Samuel

Attachment: patch
Description: Text document

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