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Re: [PATCHv2 1/2] x86/boot/compressed/64: Set up GOT for paging_prepare() and cleanup_trampoline()




On Wed, 16 May 2018, Kirill A. Shutemov wrote:

> Eric and Hugh have reported instant reboot due to my recent changes in
> decompression code.
> 
> The root cause is that I didn't realize that we need to adjust GOT to be
> able to run C code that early.
> 
> The problem is only visible with an older toolchain. Binutils >= 2.24 is
> able to eliminate GOT references by replacing them with RIP-relative
> address loads[1].
> 
> We need to adjust GOT two times:
>  - before calling paging_prepare() using the initial load address
>  - before calling C code from the relocated kernel
> 
> [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=80d873266dec
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Fixes: 194a9749c73d ("x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G")
> Reported-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>

Very nice and well done!

Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>