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>

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 3c00020..1a52e14 100644 (file)
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -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)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 573fa87..ed6f6c7 100644 (file)
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -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