[1/3] powerpc: Redefine TIF_32BITS thread flag

[Michael Ellerman]

On Thu, 2018-09-20 at 16:45:05 UTC, Breno Leitao wrote:
> Moving TIF_32BIT to use bit 20 instead of 4 in the task flag field.
> 
> This change is making room for an upcoming new task macro
> (_TIF_SYSCALL_EMU) which is preferred to set a bit in the lower 16-bits
> part of the word.
> 
> This upcoming flag macro will take part in a composed macro
> (_TIF_SYSCALL_DOTRACE) which will contain other flags as well, and it is
> preferred that the whole _TIF_SYSCALL_DOTRACE macro only sets the lower 16
> bits of a word, so, it could be handled using immediate operations (as load
> immediate, add immediate, ...) where the immediate operand (SI) is limited
> to 16-bits.
> 
> Another possible solution would be using the LOAD_REG_IMMEDIATE() macro
> to load a full 64-bits word immediate, but it takes 5 operations instead of
> one.
> 
> Having TIF_32BITS being redefined to use an upper bit is not a problem
> since there is only one place in the assembly code where TIF_32BIT is being
> used, and it could be replaced with an operation with right shift (addis),
> since it is used alone, i.e. not being part of a composed macro, which has
> different bits set, and would require LOAD_REG_IMMEDIATE().
> 
> Tested on a 64 bits Big Endian machine running a 32 bits task.
> 
> Signed-off-by: Breno Leitao <leitao at debian.org>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/16d7c69c898531210d13dbd1eb2053

cheers