On 01.10.16 19:31, Stefan Brüns wrote:

allocate_pool has to return a buffer which is 8-byte aligned. Shift the region returned by allocate_pages by 8 byte and store the size in the headroom. The 8 byte overhead is neglegible, but provides the required size when freeing the allocation later.

Signed-off-by: Stefan Brüns stefan.bruens@rwth-aachen.de

lib/efi_loader/efi_boottime.c | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c index 784891b..c413ecb 100644 --- a/lib/efi_loader/efi_boottime.c +++ b/lib/efi_loader/efi_boottime.c @@ -135,19 +135,37 @@ static efi_status_t EFIAPI efi_allocate_pool(int pool_type, unsigned long size, { efi_status_t r; efi_physical_addr_t t;

• u64 num_pages = (size + 8 + EFI_PAGE_MASK) >> EFI_PAGE_SHIFT;

Would it make things more readable if you used sizeof(u64) here?

Also, it's great to have a nice patch description which described why we have the 8 byte padding here, but we definitely need it as comment in the code as well. Otherwise people 2 years from now will have no idea why we allocate 8 bytes more ;). At least not without reverse engineering the source.

EFI_ENTRY("%d, %ld, %p", pool_type, size, buffer);

• r = efi_allocate_pages(0, pool_type, (size + 0xfff) >> 12, &t);
• *buffer = (void *)(uintptr_t)t;

• if (size == 0) {

• *buffer = NULL;
  

• return EFI_EXIT(EFI_SUCCESS);
  

• }
• r = efi_allocate_pages(0, pool_type, num_pages, &t);
• if (r == EFI_SUCCESS) {

• *(u64 *)(uintptr_t)t = num_pages;
  

I would prefer if we could make that cast a bit more expressive. How about

u64 *num_pages_hint = (void *)(uintptr_t)t;

*num_pages_hint = num_pages; *buffer = &num_pages_hint[1];

or maybe even better would be a trivial struct. Something like

struct efi_pool_allocation { u64 num_pages; char data[]; };

Then you could basically write mostly self-documenting code:

struct efi_pool_alloction *alloc = (void *)(uintptr_t)t;

alloc->num_pages = num_pages; *buffer = alloc->data;

I would still prefer if you could write a comment about what's going on, but with this it's much more obvious IMHO.

• *buffer = (void *)(uintptr_t)(t + 8);
  

• }
• return EFI_EXIT(r);

}

static efi_status_t EFIAPI efi_free_pool(void *buffer) { efi_status_t r;

• u64 num_pages;

  EFI_ENTRY("%p", buffer);

• r = efi_free_pages((ulong)buffer, 0);

• buffer = (char *)(buffer) - 8;
• assert(((ulong)buffer & EFI_PAGE_MASK) == 0);
• num_pages = *(u64 *)buffer;

With the struct, this could look a lot cleaner too:

struct efi_pool_alloction *alloc = container_of(buffer, struct efi_pool_alloction, data);

/* Pool allocations always happen on page boundaries */ assert(!((uintptr_t)alloc & EFI_PAGE_MASK)); r = efi_free_pages((uintptr_t)alloc->data, alloc->num_pages);

Alex

• r = efi_free_pages((ulong)buffer, num_pages); return EFI_EXIT(r);

}