Re: [Xen-devel] [PATCH v4 13/16] livepatch: Initial ARM32 support.

[Julien Grall <julien.grall@xxxxxxx>]

Hello Konrad,

On 16/09/2016 18:38, Konrad Rzeszutek Wilk wrote:
> The patch piggybacks on: livepatch: Initial ARM64 support, which
> brings up all of the neccessary livepatch infrastructure pieces in.
s/neccessary/necessary/

> This patch adds three major pieces:
>
>  1) ELF relocations. ARM32 uses SHT_REL instead of SHT_RELA which
>     means the adddendum had to be extracted from within the
>     instruction. Which required parsing BL/BLX, B/BL<cond>,
>     MOVT, and MOVW instructions.
>
>     The code was written from scratch using the ARM ELF manual
>     (and the ARM Architecture Reference Manual)
>
>  2) Inserting an trampoline. We use the B (branch to address)
>     which uses an offset that is based on the PC value: PC + imm32.
>     Because we insert the branch at the start of the old function
>     we have to account for the instruction already being fetched
>     and subtract -8 from the delta (new_addr - old_addr). See
>     ARM DDI 0406C.c, see A2.3 (pg 45) and A8.8.18 pg (pg 334,335)
>
>  3) Allows the test-cases to be built under ARM 32.
>     The "livepatch: tests: Make them compile under ARM64"
>     put in the right infrastructure for it and we piggyback on it.
>
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx> [for non-ARM parts]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Acked-by: Julien Grall <julien.grall@xxxxxxx>

Regards,

--
Julien Grall

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