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Subject[tip: x86/asm] x86/boot: Simplify calculation of output address
The following commit has been merged into the x86/asm branch of tip:

Commit-ID: 183ef7adf4ed638ac0fb0c3c9a71fc00e8512b61
Gitweb: https://git.kernel.org/tip/183ef7adf4ed638ac0fb0c3c9a71fc00e8512b61
Author: Arvind Sankar <nivedita@alum.mit.edu>
AuthorDate: Tue, 07 Jan 2020 14:44:34 -05:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 23 Jan 2020 11:58:43 +01:00

x86/boot: Simplify calculation of output address

Condense the calculation of decompressed kernel start a little.

Committer notes:

before:

ebp = ebx - (init_size - _end)

after:

eax = (ebx + _end) - init_size

where in both ebx contains the temporary address the kernel is moved to
for in-place decompression.

The before and after difference in register state is %eax and %ebp
but that is immaterial because the compressed image is not built with
-mregparm, i.e., all arguments of the following extract_kernel() call
are passed on the stack.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200107194436.2166846-1-nivedita@alum.mit.edu
---
arch/x86/boot/compressed/head_32.S | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index f2dfd6d..1cc55c7 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -240,11 +240,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
/* push arguments for extract_kernel: */
pushl $z_output_len /* decompressed length, end of relocs */

- movl BP_init_size(%esi), %eax
- subl $_end, %eax
- movl %ebx, %ebp
- subl %eax, %ebp
- pushl %ebp /* output address */
+ leal _end(%ebx), %eax
+ subl BP_init_size(%esi), %eax
+ pushl %eax /* output address */

pushl $z_input_len /* input_len */
leal input_data(%ebx), %eax
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