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ARC: entry: use gp to cache task pointer (vs. r25)

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The motivation is eventual ABI considerations for ARCv3 but even without
it this change us worthwhile as diffstat reduces 100 net lines

r25 is a callee saved register, normally not saved by entry code in
pt_regs. However because of its usage in CONFIG_ARC_CURR_IN_REG it needs
to be. This in turn requires a whole bunch of special casing when we
need to access r25. Then there is distinction between user mode r25 vs.
kernel mode r25 - hence distinct SAVE_CALLEE_SAVED_{USER,KERNEL}

Instead use gp which is a scratch register and thus saved already in entry
code. This cleans things up significantly and much nocer on eyes:

 - SAVE_CALLEE_SAVED_{USER,KERNEL} are now exactly same
 - no special user_r25 slot in pt_reggs

Note that typical global asm registers are callee-saved (r25), but gp is
not callee-saved thus needs additional -ffixed-<reg> toggle

Signed-off-by: Vineet Gupta <vgupta@kernel.org>
This commit is contained in:
Vineet Gupta
2020-05-12 22:18:08 -07:00
parent fad84e39f1
commit cfca4b5abe
13 changed files with 60 additions and 156 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/arc/include/asm/current.h
+1 -1
View File
@@ -13,7 +13,7 @@
#ifdef CONFIG_ARC_CURR_IN_REG
register struct task_struct *curr_arc asm("r25");
register struct task_struct *curr_arc asm("gp");
#define current (curr_arc)
#else
arch/arc/include/asm/entry-arcv2.h
+6 -11
View File
@@ -18,7 +18,6 @@
* | orig_r0 |
* | event/ECR |
* | bta |
* | user_r25 |
* | gp |
* | fp |
* | sp |
@@ -56,7 +55,7 @@
; hardware does even if CONFIG_ARC_IRQ_NO_AUTOSAVE
; 4. Auto save: (optional) r0-r11, blink, LPE,LPS,LPC, JLI,LDI,EI
;
; (B) Manually saved some regs: r12,r25,r30, sp,fp,gp, ACCL pair
; (B) Manually saved some regs: r12,r30, sp,fp,gp, ACCL pair
#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
; carve pt_regs on stack (case #3), PC/STAT32 already on stack
@@ -157,17 +156,17 @@
st r10, [sp, PT_sp] ; SP (pt_regs->sp)
#ifdef CONFIG_ARC_CURR_IN_REG
st r25, [sp, PT_user_r25]
GET_CURR_TASK_ON_CPU r25
#endif
#ifdef CONFIG_ARC_HAS_ACCL_REGS
ST2 r58, r59, PT_r58
#endif
/* clobbers r10, r11 registers pair */
DSP_SAVE_REGFILE_IRQ
#ifdef CONFIG_ARC_CURR_IN_REG
GET_CURR_TASK_ON_CPU gp
#endif
.endm
/*------------------------------------------------------------------------*/
@@ -188,10 +187,6 @@
sr r10, [AUX_USER_SP]
1:
#ifdef CONFIG_ARC_CURR_IN_REG
ld r25, [sp, PT_user_r25]
#endif
/* clobbers r10, r11 registers pair */
DSP_RESTORE_REGFILE_IRQ
arch/arc/include/asm/entry-compact.h
+11 -24
View File
@@ -151,14 +151,6 @@
/* ARC700 doesn't provide auto-stack switching */
SWITCH_TO_KERNEL_STK
#ifdef CONFIG_ARC_CURR_IN_REG
/* Treat r25 as scratch reg (save on stack) and load with "current" */
PUSH r25
GET_CURR_TASK_ON_CPU r25
#else
sub sp, sp, 4
#endif
st.a r0, [sp, -8] /* orig_r0 needed for syscall (skip ECR slot) */
sub sp, sp, 4 /* skip pt_regs->sp, already saved above */
@@ -179,6 +171,11 @@
lr r10, [ecr]
st r10, [sp, PT_event] /* EV_Trap expects r10 to have ECR */
#ifdef CONFIG_ARC_CURR_IN_REG
/* gp already saved on stack: now load with "current" */
GET_CURR_TASK_ON_CPU gp
#endif
.endm
/*--------------------------------------------------------------
@@ -208,11 +205,8 @@
POP gp
RESTORE_R12_TO_R0
#ifdef CONFIG_ARC_CURR_IN_REG
ld r25, [sp, 12]
#endif
ld sp, [sp] /* restore original sp */
/* orig_r0, ECR, user_r25 skipped automatically */
/* orig_r0, ECR skipped automatically */
.endm
/* Dummy ECR values for Interrupts */
@@ -229,13 +223,6 @@
SWITCH_TO_KERNEL_STK
#ifdef CONFIG_ARC_CURR_IN_REG
/* Treat r25 as scratch reg (save on stack) and load with "current" */
PUSH r25
GET_CURR_TASK_ON_CPU r25
#else
sub sp, sp, 4
#endif
PUSH 0x003\LVL\()abcd /* Dummy ECR */
sub sp, sp, 8 /* skip orig_r0 (not needed)
@@ -255,6 +242,10 @@
PUSHAX lp_start
PUSHAX bta_l\LVL\()
#ifdef CONFIG_ARC_CURR_IN_REG
/* gp already saved on stack: now load with "current" */
GET_CURR_TASK_ON_CPU gp
#endif
.endm
/*--------------------------------------------------------------
@@ -282,11 +273,7 @@
POP gp
RESTORE_R12_TO_R0
#ifdef CONFIG_ARC_CURR_IN_REG
ld r25, [sp, 12]
#endif
ld sp, [sp] /* restore original sp */
/* orig_r0, ECR, user_r25 skipped automatically */
ld sp, [sp] /* restore original sp; orig_r0, ECR skipped implicitly */
.endm
/* Get thread_info of "current" tsk */
arch/arc/include/asm/entry.h
+31 -80
View File
@@ -91,7 +91,7 @@
* Helpers to save/restore callee-saved regs:
* used by several macros below
*-------------------------------------------------------------*/
.macro SAVE_R13_TO_R24
.macro SAVE_R13_TO_R25
PUSH r13
PUSH r14
PUSH r15
@@ -104,9 +104,11 @@
PUSH r22
PUSH r23
PUSH r24
PUSH r25
.endm
.macro RESTORE_R24_TO_R13
.macro RESTORE_R25_TO_R13
POP r25
POP r24
POP r23
POP r22
@@ -121,81 +123,31 @@
POP r13
.endm
/*--------------------------------------------------------------
* Collect User Mode callee regs as struct callee_regs - needed by
* fork/do_signal/unaligned-access-emulation.
* (By default only scratch regs are saved on entry to kernel)
*
* Special handling for r25 if used for caching Task Pointer.
* It would have been saved in task->thread.user_r25 already, but to keep
* the interface same it is copied into regular r25 placeholder in
* struct callee_regs.
*-------------------------------------------------------------*/
/*
* save user mode callee regs as struct callee_regs
* - needed by fork/do_signal/unaligned-access-emulation.
*/
.macro SAVE_CALLEE_SAVED_USER
mov r12, sp ; save SP as ref to pt_regs
SAVE_R13_TO_R24
#ifdef CONFIG_ARC_CURR_IN_REG
; Retrieve orig r25 and save it with rest of callee_regs
ld r12, [r12, PT_user_r25]
PUSH r12
#else
PUSH r25
#endif
SAVE_R13_TO_R25
.endm
/*--------------------------------------------------------------
* Save kernel Mode callee regs at the time of Contect Switch.
*
* Special handling for r25 if used for caching Task Pointer.
* Kernel simply skips saving it since it will be loaded with
* incoming task pointer anyways
*-------------------------------------------------------------*/
.macro SAVE_CALLEE_SAVED_KERNEL
SAVE_R13_TO_R24
#ifdef CONFIG_ARC_CURR_IN_REG
sub sp, sp, 4
#else
PUSH r25
#endif
.endm
/*--------------------------------------------------------------
* Opposite of SAVE_CALLEE_SAVED_KERNEL
*-------------------------------------------------------------*/
.macro RESTORE_CALLEE_SAVED_KERNEL
#ifdef CONFIG_ARC_CURR_IN_REG
add sp, sp, 4 /* skip usual r25 placeholder */
#else
POP r25
#endif
RESTORE_R24_TO_R13
.endm
/*--------------------------------------------------------------
* Opposite of SAVE_CALLEE_SAVED_USER
*
* ptrace tracer or unaligned-access fixup might have changed a user mode
* callee reg which is saved back to usual r25 storage location
*-------------------------------------------------------------*/
/*
* restore user mode callee regs as struct callee_regs
* - could have been changed by ptrace tracer or unaligned-access fixup
*/
.macro RESTORE_CALLEE_SAVED_USER
RESTORE_R25_TO_R13
.endm
#ifdef CONFIG_ARC_CURR_IN_REG
POP r12
#else
POP r25
#endif
RESTORE_R24_TO_R13
/*
* save/restore kernel mode callee regs at the time of context switch
*/
.macro SAVE_CALLEE_SAVED_KERNEL
SAVE_R13_TO_R25
.endm
; SP is back to start of pt_regs
#ifdef CONFIG_ARC_CURR_IN_REG
st r12, [sp, PT_user_r25]
#endif
.macro RESTORE_CALLEE_SAVED_KERNEL
RESTORE_R25_TO_R13
.endm
/*--------------------------------------------------------------
@@ -231,10 +183,10 @@
#ifdef CONFIG_SMP
/*-------------------------------------------------
/*
* Retrieve the current running task on this CPU
* 1. Determine curr CPU id.
* 2. Use it to index into _current_task[ ]
* - loads it from backing _current_task[] (and can't use the
* caching reg for current task
*/
.macro GET_CURR_TASK_ON_CPU reg
GET_CPU_ID \reg
@@ -256,7 +208,7 @@
add2 \tmp, @_current_task, \tmp
st \tsk, [\tmp]
#ifdef CONFIG_ARC_CURR_IN_REG
mov r25, \tsk
mov gp, \tsk
#endif
.endm
@@ -271,21 +223,20 @@
.macro SET_CURR_TASK_ON_CPU tsk, tmp
st \tsk, [@_current_task]
#ifdef CONFIG_ARC_CURR_IN_REG
mov r25, \tsk
mov gp, \tsk
#endif
.endm
#endif /* SMP / UNI */
/* ------------------------------------------------------------------
/*
* Get the ptr to some field of Current Task at @off in task struct
* -Uses r25 for Current task ptr if that is enabled
* - Uses current task cached in reg if enabled
*/
#ifdef CONFIG_ARC_CURR_IN_REG
.macro GET_CURR_TASK_FIELD_PTR off, reg
add \reg, r25, \off
add \reg, gp, \off
.endm
#else
arch/arc/include/asm/ptrace.h
+1 -5
View File
@@ -52,11 +52,9 @@ struct pt_regs {
};
unsigned long event;
};
unsigned long user_r25;
};
#define MAX_REG_OFFSET offsetof(struct pt_regs, user_r25)
#define MAX_REG_OFFSET offsetof(struct pt_regs, event)
#else
@@ -79,8 +77,6 @@ struct pt_regs {
unsigned long bta; /* bta_l1, bta_l2, erbta */
unsigned long user_r25;
unsigned long r26; /* gp */
unsigned long fp;
unsigned long sp; /* user/kernel sp depending on where we came from */