Re: [PATCH v3 6/7] x86/boot: Remove runtime relocations from head_{32,64}.S

[Kees Cook]

On Mon, Jun 29, 2020 at 10:09:27AM -0400, Arvind Sankar wrote:
> The BFD linker generates runtime relocations for z_input_len and
> z_output_len, even though they are absolute symbols.
> 
> This is fixed for binutils-2.35 [1]. Work around this for earlier
> versions by defining two variables input_len and output_len in addition
> to the symbols, and use them via position-independent references.
> 
> This eliminates the last two runtime relocations in the head code and
> allows us to drop the -z noreloc-overflow flag to the linker.
> 
> [1] https://sourceware.org/bugzilla/show_bug.cgi?id=25754
> 
> Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx>
> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/Makefile  |  8 --------
>  arch/x86/boot/compressed/head_32.S | 17 ++++++++---------
>  arch/x86/boot/compressed/head_64.S |  4 ++--
>  arch/x86/boot/compressed/mkpiggy.c |  6 ++++++
>  4 files changed, 16 insertions(+), 19 deletions(-)

I continue to really enjoy the smaller code. Anything that makes
mkpiggy.c smaller is a win. :)

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook