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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Thu, 21 Apr 2022 15:24:15 +1000
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Subject: [PATCH] mm: When adding a region, merge with region after as well as
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before
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On x86_64-efi (at least) regions seem to be added from top down. The mm
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code will merge a new region with an existing region that comes
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immediately before the new region. This allows larger allocations to be
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satisfied that would otherwise be the case.
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On powerpc-ieee1275, however, regions are added from bottom up. So if
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we add 3x 32MB regions, we can still only satisfy a 32MB allocation,
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rather than the 96MB allocation we might otherwise be able to satisfy.
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* Define 'post_size' as being bytes lost to the end of an allocation
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due to being given weird sizes from firmware that are not multiples
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of GRUB_MM_ALIGN.
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* Allow merging of regions immediately _after_ existing regions, not
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just before. As with the other approach, we create an allocated
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block to represent the new space and the pass it to grub_free() to
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get the metadata right.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Tested-by: Stefan Berger <stefanb@linux.ibm.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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Tested-by: Patrick Steinhardt <ps@pks.im>
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(cherry picked from commit 052e6068be622ff53f1238b449c300dbd0a8abcd)
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---
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grub-core/kern/mm.c | 128 +++++++++++++++++++++++++++++-----------------
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include/grub/mm_private.h | 9 ++++
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2 files changed, 91 insertions(+), 46 deletions(-)
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diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
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index 1cbf98c7ab..7be33e23bf 100644
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--- a/grub-core/kern/mm.c
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+++ b/grub-core/kern/mm.c
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@@ -130,53 +130,88 @@ grub_mm_init_region (void *addr, grub_size_t size)
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/* Attempt to merge this region with every existing region */
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for (p = &grub_mm_base, q = *p; q; p = &(q->next), q = *p)
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- /*
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- * Is the new region immediately below an existing region? That
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- * is, is the address of the memory we're adding now (addr) + size
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- * of the memory we're adding (size) + the bytes we couldn't use
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- * at the start of the region we're considering (q->pre_size)
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- * equal to the address of q? In other words, does the memory
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- * looks like this?
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- *
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- * addr q
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- * |----size-----|-q->pre_size-|<q region>|
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- */
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- if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)
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- {
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- /*
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- * Yes, we can merge the memory starting at addr into the
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- * existing region from below. Align up addr to GRUB_MM_ALIGN
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- * so that our new region has proper alignment.
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- */
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- r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
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- /* Copy the region data across */
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- *r = *q;
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- /* Consider all the new size as pre-size */
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- r->pre_size += size;
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+ {
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+ /*
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+ * Is the new region immediately below an existing region? That
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+ * is, is the address of the memory we're adding now (addr) + size
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+ * of the memory we're adding (size) + the bytes we couldn't use
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+ * at the start of the region we're considering (q->pre_size)
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+ * equal to the address of q? In other words, does the memory
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+ * looks like this?
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+ *
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+ * addr q
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+ * |----size-----|-q->pre_size-|<q region>|
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+ */
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+ if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)
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+ {
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+ /*
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+ * Yes, we can merge the memory starting at addr into the
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+ * existing region from below. Align up addr to GRUB_MM_ALIGN
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+ * so that our new region has proper alignment.
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+ */
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+ r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
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+ /* Copy the region data across */
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+ *r = *q;
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+ /* Consider all the new size as pre-size */
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+ r->pre_size += size;
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- /*
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- * If we have enough pre-size to create a block, create a
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- * block with it. Mark it as allocated and pass it to
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- * grub_free (), which will sort out getting it into the free
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- * list.
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- */
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- if (r->pre_size >> GRUB_MM_ALIGN_LOG2)
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- {
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- h = (grub_mm_header_t) (r + 1);
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- /* block size is pre-size converted to cells */
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- h->size = (r->pre_size >> GRUB_MM_ALIGN_LOG2);
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- h->magic = GRUB_MM_ALLOC_MAGIC;
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- /* region size grows by block size converted back to bytes */
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- r->size += h->size << GRUB_MM_ALIGN_LOG2;
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- /* adjust pre_size to be accurate */
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- r->pre_size &= (GRUB_MM_ALIGN - 1);
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- *p = r;
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- grub_free (h + 1);
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- }
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- /* Replace the old region with the new region */
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- *p = r;
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- return;
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- }
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+ /*
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+ * If we have enough pre-size to create a block, create a
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+ * block with it. Mark it as allocated and pass it to
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+ * grub_free (), which will sort out getting it into the free
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+ * list.
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+ */
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+ if (r->pre_size >> GRUB_MM_ALIGN_LOG2)
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+ {
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+ h = (grub_mm_header_t) (r + 1);
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+ /* block size is pre-size converted to cells */
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+ h->size = (r->pre_size >> GRUB_MM_ALIGN_LOG2);
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+ h->magic = GRUB_MM_ALLOC_MAGIC;
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+ /* region size grows by block size converted back to bytes */
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+ r->size += h->size << GRUB_MM_ALIGN_LOG2;
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+ /* adjust pre_size to be accurate */
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+ r->pre_size &= (GRUB_MM_ALIGN - 1);
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+ *p = r;
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+ grub_free (h + 1);
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+ }
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+ /* Replace the old region with the new region */
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+ *p = r;
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+ return;
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+ }
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+
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+ /*
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+ * Is the new region immediately above an existing region? That
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+ * is:
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+ * q addr
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+ * |<q region>|-q->post_size-|----size-----|
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+ */
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+ if ((grub_uint8_t *) q + sizeof (*q) + q->size + q->post_size ==
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+ (grub_uint8_t *) addr)
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+ {
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+ /*
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+ * Yes! Follow a similar pattern to above, but simpler.
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+ * Our header starts at address - post_size, which should align us
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+ * to a cell boundary.
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+ *
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+ * Cast to (void *) first to avoid the following build error:
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+ * kern/mm.c: In function ‘grub_mm_init_region’:
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+ * kern/mm.c:211:15: error: cast increases required alignment of target type [-Werror=cast-align]
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+ * 211 | h = (grub_mm_header_t) ((grub_uint8_t *) addr - q->post_size);
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+ * | ^
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+ * It is safe to do that because proper alignment is enforced in grub_mm_size_sanity_check().
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+ */
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+ h = (grub_mm_header_t)(void *) ((grub_uint8_t *) addr - q->post_size);
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+ /* our size is the allocated size plus post_size, in cells */
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+ h->size = (size + q->post_size) >> GRUB_MM_ALIGN_LOG2;
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+ h->magic = GRUB_MM_ALLOC_MAGIC;
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+ /* region size grows by block size converted back to bytes */
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+ q->size += h->size << GRUB_MM_ALIGN_LOG2;
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+ /* adjust new post_size to be accurate */
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+ q->post_size = (q->post_size + size) & (GRUB_MM_ALIGN - 1);
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+ grub_free (h + 1);
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+ return;
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+ }
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+ }
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/* Allocate a region from the head. */
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r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
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@@ -195,6 +230,7 @@ grub_mm_init_region (void *addr, grub_size_t size)
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r->first = h;
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r->pre_size = (grub_addr_t) r - (grub_addr_t) addr;
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r->size = (h->size << GRUB_MM_ALIGN_LOG2);
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+ r->post_size = size - r->size;
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/* Find where to insert this region. Put a smaller one before bigger ones,
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to prevent fragmentation. */
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diff --git a/include/grub/mm_private.h b/include/grub/mm_private.h
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index a688b92a83..96c2d816be 100644
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--- a/include/grub/mm_private.h
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+++ b/include/grub/mm_private.h
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@@ -81,8 +81,17 @@ typedef struct grub_mm_region
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*/
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grub_size_t pre_size;
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+ /*
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+ * Likewise, the post-size is the number of bytes we wasted at the end
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+ * of the allocation because it wasn't a multiple of GRUB_MM_ALIGN
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+ */
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+ grub_size_t post_size;
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+
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/* How many bytes are in this region? (free and allocated) */
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grub_size_t size;
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+
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+ /* pad to a multiple of cell size */
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+ char padding[3 * GRUB_CPU_SIZEOF_VOID_P];
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}
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*grub_mm_region_t;
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