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SubjectRe: [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage
On Thu, Jan 09, 2020 at 10:02:17AM -0500, Arvind Sankar wrote:
> Commit 5b11f1cee579 ("x86, boot: straighten out ranges to copy/zero in
> compressed/head*.S") introduced a separate .pgtable section, splitting
> it out from the rest of .bss. This section was added without the
> writeable flag, marking it as read-only. This results in the linker
> putting the .rela.dyn section (containing bogus dynamic relocations from
> head_64.o) after the .bss and .pgtable sections.
>
> When we use objcopy to convert compressed/vmlinux into a binary for the
> bzImage, the .bss and .pgtable sections get materialized as ~176KiB of
> zero bytes in the binary in order to place .rela.dyn at the correct
> location.
>
> Fix this by marking .pgtable as writeable. This moves the .rela.dyn
> section earlier so that .bss and .pgtable are the last allocated
> sections and so don't appear in bzImage.
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> ---
> arch/x86/boot/compressed/head_64.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index 58a512e33d8d..6eb30f8a3ce7 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -709,7 +709,7 @@ SYM_DATA_END_LABEL(boot_stack, SYM_L_LOCAL, boot_stack_end)
> /*
> * Space for page tables (not in .bss so not zeroed)
> */
> - .section ".pgtable","a",@nobits
> + .section ".pgtable","aw",@nobits
> .balign 4096
> SYM_DATA_LOCAL(pgtable, .fill BOOT_PGT_SIZE, 1, 0)
>
> --
> 2.24.1
>

Gentle reminder.

https://lore.kernel.org/lkml/20200109150218.16544-1-nivedita@alum.mit.edu

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