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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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