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powerpc: Redefine TIF_32BITS thread flag 

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@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Breno Leitao 2018-09-20 13:45:05 -03:00 committed by Michael Ellerman
parent 06ec27aea9
commit 16d7c69c89
2 changed files with 2 additions and 2 deletions
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2
arch/powerpc/include/asm/thread_info.h
View File

@ -81,7 +81,6 @@ extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src
#define TIF_SIGPENDING 1 /* signal pending */
#define TIF_NEED_RESCHED 2 /* rescheduling necessary */
#define TIF_FSCHECK 3 /* Check FS is USER_DS on return */
#define TIF_32BIT 4 /* 32 bit binary */
#define TIF_RESTORE_TM 5 /* need to restore TM FP/VEC/VSX */
#define TIF_PATCH_PENDING 6 /* pending live patching update */
#define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
@ -100,6 +99,7 @@ extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src
#define TIF_ELF2ABI 18 /* function descriptors must die! */
#endif
#define TIF_POLLING_NRFLAG 19 /* true if poll_idle() is polling TIF_NEED_RESCHED */
#define TIF_32BIT 20 /* 32 bit binary */
/* as above, but as bit values */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)

2
arch/powerpc/kernel/entry_64.S
View File

@ -171,7 +171,7 @@ system_call: /* label this so stack traces look sane */
* based on caller's run-mode / personality.
*/
ld r11,SYS_CALL_TABLE@toc(2)
andi. r10,r10,_TIF_32BIT
andis. r10,r10,_TIF_32BIT@h
beq 15f
addi r11,r11,8 /* use 32-bit syscall entries */
clrldi r3,r3,32