Commit 183ef7ad authored Jan 07, 2020 by Arvind Sankar Committed by Borislav Petkov Jan 23, 2020

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

parent b2b1d94c

arch/x86/boot/compressed/head_32.S

+3 −5

Original line number	Diff line number	Diff line
		@@ -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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