[U-Boot] [PATCH 0/3] ARM: use r9 for gd instead of r8

Benoît Thébaudeau
2013-08-11T22:08:59Z

Dear Jeroen Hofstee,

On Sunday, August 11, 2013 10:58:36 PM, Jeroen Hofstee wrote:
> To be EABI compliant (r9 is a platform specific register) and as
> a prepration for building u-boot with clang/llvm (with does / will
> support r9 as reserved register), store the pointer to gd in r9.

If r9 is reserved, I understand that its current usage may conflict with clang's
but why would gd have to be stored in r9 for clang? Moreover, if r9 is reserved
for clang (reserved for what?), why can it be used for gd?

I'm also wondering if r9 as initialized by relocate.S is not sometimes used by
GCC to handle position-independent code within generated code, i.e. like the
static base feature described for r9 as a possible usage in the ARM EABI AAPCS
document (5.1.1). If this is the case, changing r9 to gd would break GCC code at
runtime.

Best regards,
Beno?t