Commit 195b58ad authored by Russell King's avatar Russell King
Browse files

ARM: Avoid writing to control register on every exception

If we are not changing the control register value, avoid writing to it.
Writes to the control register can be very expensive, taking around a
hundred cycles or so.
Signed-off-by: default avatarRussell King <>
parent 8b521cb2
......@@ -321,6 +321,9 @@ ENDPROC(__pabt_svc)
ARM( stmib sp, {r1 - r12} )
THUMB( stmia sp, {r0 - r12} )
ATRAP( mrc p15, 0, r7, c1, c0, 0)
ATRAP( ldr r8, .LCcralign)
ldmia r0, {r3 - r5}
add r0, sp, #S_PC @ here for interlock avoidance
mov r6, #-1 @ "" "" "" ""
......@@ -328,6 +331,8 @@ ENDPROC(__pabt_svc)
str r3, [sp] @ save the "real" r0 copied
@ from the exception stack
ATRAP( ldr r8, [r8, #0])
@ We are now ready to fill in the remaining blanks on the stack:
......@@ -341,10 +346,9 @@ ENDPROC(__pabt_svc)
ARM( stmdb r0, {sp, lr}^ )
THUMB( store_user_sp_lr r0, r1, S_SP - S_PC )
@ Enable the alignment trap while in kernel mode
alignment_trap r0, .LCcralign
ATRAP( teq r8, r7)
ATRAP( mcrne p15, 0, r8, c1, c0, 0)
@ Clear FP to mark the first stack frame
......@@ -366,7 +366,7 @@ ENTRY(vector_swi)
str r0, [sp, #S_OLD_R0] @ Save OLD_R0
alignment_trap ip, __cr_alignment
alignment_trap r10, ip, __cr_alignment
get_thread_info tsk
......@@ -37,11 +37,19 @@
.macro alignment_trap, rtemp, label
ldr \rtemp, \label
ldr \rtemp, [\rtemp]
mcr p15, 0, \rtemp, c1, c0
#define ATRAP(x...) x
#define ATRAP(x...)
.macro alignment_trap, rtmp1, rtmp2, label
mrc p15, 0, \rtmp2, c1, c0, 0
ldr \rtmp1, \label
ldr \rtmp1, [\rtmp1]
teq \rtmp1, \rtmp2
mcrne p15, 0, \rtmp1, c1, c0, 0
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