[PATCH 4/5] ARCv2: entry: rewrite to enable use of double load/stores LDD/STD

From: Vineet Gupta
Date: Fri May 17 2019 - 15:34:45 EST

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- the motivation was to be remove blatent copy-paste due to hasty support
of CONFIG_ARC_IRQ_NO_AUTOSAVE support

- but with refactoring we could use LDD/STD to greatly optimize the code

Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
---
arch/arc/include/asm/entry-arcv2.h | 297 +++++++++++++++++--------------------
arch/arc/include/asm/linkage.h | 18 +++
arch/arc/kernel/asm-offsets.c | 7 +
arch/arc/kernel/entry-arcv2.S | 4 +-
4 files changed, 167 insertions(+), 159 deletions(-)

diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
index beaf655666cb..0733752ce7fe 100644
--- a/arch/arc/include/asm/entry-arcv2.h
+++ b/arch/arc/include/asm/entry-arcv2.h
@@ -46,7 +46,8 @@
*/

/*------------------------------------------------------------------------*/
-.macro INTERRUPT_PROLOGUE called_from
+.macro INTERRUPT_PROLOGUE
+
; (A) Before jumping to Interrupt Vector, hardware micro-ops did following:
; 1. SP auto-switched to kernel mode stack
; 2. STATUS32.Z flag set if in U mode at time of interrupt (U:1,K:0)
@@ -57,39 +58,87 @@
; (B) Manually saved some regs: r12,r25,r30, sp,fp,gp, ACCL pair

#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
-.ifnc \called_from, exception
- st.as r9, [sp, -10] ; save r9 in it's final stack slot
- sub sp, sp, 12 ; skip JLI, LDI, EI
-
- PUSH lp_count
- PUSHAX lp_start
- PUSHAX lp_end
- PUSH blink
-
- PUSH r11
- PUSH r10
-
- sub sp, sp, 4 ; skip r9
-
- PUSH r8
- PUSH r7
- PUSH r6
- PUSH r5
- PUSH r4
- PUSH r3
- PUSH r2
- PUSH r1
- PUSH r0
-.endif
-#endif
+ ; carve pt_regs on stack (case #3), PC/STAT32 already on stack
+ sub sp, sp, SZ_PT_REGS - 8

-#ifdef CONFIG_ARC_HAS_ACCL_REGS
- PUSH r59
- PUSH r58
+ __SAVE_REGFILE_HARD
+#else
+ ; carve pt_regs on stack (case #4), which grew partially already
+ sub sp, sp, PT_r0
#endif

- PUSH r30
- PUSH r12
+ __SAVE_REGFILE_SOFT
+.endm
+
+/*------------------------------------------------------------------------*/
+.macro EXCEPTION_PROLOGUE
+
+ ; (A) Before jumping to Exception Vector, hardware micro-ops did following:
+ ; 1. SP auto-switched to kernel mode stack
+ ; 2. STATUS32.Z flag set if in U mode at time of exception (U:1,K:0)
+ ;
+ ; (B) Manually save the complete reg file below
+
+ sub sp, sp, SZ_PT_REGS ; carve pt_regs
+
+ ; _HARD saves r10 clobbered by _SOFT as scratch hence comes first
+
+ __SAVE_REGFILE_HARD
+ __SAVE_REGFILE_SOFT
+
+ st r0, [sp] ; orig_r0
+
+ lr r10, [eret]
+ lr r11, [erstatus]
+ ST2 r10, r11, PT_ret
+
+ lr r10, [ecr]
+ lr r11, [erbta]
+ ST2 r10, r11, PT_event
+ mov r9, r10
+
+ ; OUTPUT: r9 has ECR
+.endm
+
+/*------------------------------------------------------------------------
+ * This macro saves the registers manually which would normally be autosaved
+ * by hardware on taken interrupts. It is used by
+ * - exception handlers (which don't have autosave)
+ * - interrupt autosave disabled due to CONFIG_ARC_IRQ_NO_AUTOSAVE
+ */
+.macro __SAVE_REGFILE_HARD
+
+ ST2 r0, r1, PT_r0
+ ST2 r2, r3, PT_r2
+ ST2 r4, r5, PT_r4
+ ST2 r6, r7, PT_r6
+ ST2 r8, r9, PT_r8
+ ST2 r10, r11, PT_r10
+
+ st blink, [sp, PT_blink]
+
+ lr r10, [lp_end]
+ lr r11, [lp_start]
+ ST2 r10, r11, PT_lpe
+
+ st lp_count, [sp, PT_lpc]
+
+ ; skip JLI, LDI, EI for now
+.endm
+
+/*------------------------------------------------------------------------
+ * This macros saves a bunch of other registers which can't be autosaved for
+ * various reasons:
+ * - r12: the last caller saved scratch reg since hardware saves in pairs so r0-r11
+ * - r30: free reg, used by gcc as scratch
+ * - ACCL/ACCH pair when they exist
+ */
+.macro __SAVE_REGFILE_SOFT
+
+ ST2 gp, fp, PT_r26 ; gp (r26), fp (r27)
+
+ st r12, [sp, PT_sp + 4]
+ st r30, [sp, PT_sp + 8]

; Saving pt_regs->sp correctly requires some extra work due to the way
; Auto stack switch works
@@ -100,46 +149,32 @@
; 2. Upon entry SP is always saved (for any inspection, unwinding etc),
; but on return, restored only if U mode

- lr r9, [AUX_USER_SP] ; U mode SP
+ lr r10, [AUX_USER_SP] ; U mode SP

- mov.nz r9, sp
- add.nz r9, r9, SZ_PT_REGS - PT_sp - 4 ; K mode SP
+ ; ISA requires ADD.nz to have same dest and src reg operands
+ mov.nz r10, sp
+ add.nz r10, r10, SZ_PT_REGS ; K mode SP

- PUSH r9 ; SP (pt_regs->sp)
-
- PUSH fp
- PUSH gp
+ st r10, [sp, PT_sp] ; SP (pt_regs->sp)

#ifdef CONFIG_ARC_CURR_IN_REG
- PUSH r25 ; user_r25
+ st r25, [sp, PT_user_r25]
GET_CURR_TASK_ON_CPU r25
-#else
- sub sp, sp, 4
#endif

-.ifnc \called_from, exception
- sub sp, sp, 12 ; BTA/ECR/orig_r0 placeholder per pt_regs
-.endif
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+ ST2 r58, r59, PT_sp + 12
+#endif

.endm

/*------------------------------------------------------------------------*/
-.macro INTERRUPT_EPILOGUE called_from
+.macro __RESTORE_REGFILE_SOFT

- ; INPUT: r0 has STAT32 of calling context
- ; INPUT: Z flag set if returning to K mode
-.ifnc \called_from, exception
- add sp, sp, 12 ; skip BTA/ECR/orig_r0 placeholderss
-.endif
-
-#ifdef CONFIG_ARC_CURR_IN_REG
- POP r25
-#else
- add sp, sp, 4
-#endif
+ LD2 gp, fp, PT_r26 ; gp (r26), fp (r27)

- POP gp
- POP fp
+ ld r12, [sp, PT_sp + 4]
+ ld r30, [sp, PT_sp + 8]

; Restore SP (into AUX_USER_SP) only if returning to U mode
; - for K mode, it will be implicitly restored as stack is unwound
@@ -147,129 +182,77 @@
; but that doesn't really matter
bz 1f

- POPAX AUX_USER_SP
+ ld r10, [sp, PT_sp] ; SP (pt_regs->sp)
+ sr r10, [AUX_USER_SP]
1:
- POP r12
- POP r30

-#ifdef CONFIG_ARC_HAS_ACCL_REGS
- POP r58
- POP r59
+#ifdef CONFIG_ARC_CURR_IN_REG
+ ld r25, [sp, PT_user_r25]
#endif

-#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
-.ifnc \called_from, exception
- POP r0
- POP r1
- POP r2
- POP r3
- POP r4
- POP r5
- POP r6
- POP r7
- POP r8
- POP r9
- POP r10
- POP r11
-
- POP blink
- POPAX lp_end
- POPAX lp_start
-
- POP r9
- mov lp_count, r9
-
- add sp, sp, 12 ; skip JLI, LDI, EI
- ld.as r9, [sp, -10] ; reload r9 which got clobbered
-.endif
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+ LD2 r58, r59, PT_sp + 12
#endif
-
.endm

/*------------------------------------------------------------------------*/
-.macro EXCEPTION_PROLOGUE
+.macro __RESTORE_REGFILE_HARD

- ; (A) Before jumping to Exception Vector, hardware micro-ops did following:
- ; 1. SP auto-switched to kernel mode stack
- ; 2. STATUS32.Z flag set if in U mode at time of exception (U:1,K:0)
- ;
- ; (B) Manually save the complete reg file below
+ ld blink, [sp, PT_blink]

- PUSH r9 ; freeup a register: slot of erstatus
+ LD2 r10, r11, PT_lpe
+ sr r10, [lp_end]
+ sr r11, [lp_start]

- PUSHAX eret
- sub sp, sp, 12 ; skip JLI, LDI, EI
- PUSH lp_count
- PUSHAX lp_start
- PUSHAX lp_end
- PUSH blink
+ ld r10, [sp, PT_lpc] ; lp_count can't be target of LD
+ mov lp_count, r10

- PUSH r11
- PUSH r10
+ LD2 r0, r1, PT_r0
+ LD2 r2, r3, PT_r2
+ LD2 r4, r5, PT_r4
+ LD2 r6, r7, PT_r6
+ LD2 r8, r9, PT_r8
+ LD2 r10, r11, PT_r10
+.endm

- ld.as r9, [sp, 10] ; load stashed r9 (status32 stack slot)
- lr r10, [erstatus]
- st.as r10, [sp, 10] ; save status32 at it's right stack slot

- PUSH r9
- PUSH r8
- PUSH r7
- PUSH r6
- PUSH r5
- PUSH r4
- PUSH r3
- PUSH r2
- PUSH r1
- PUSH r0
+/*------------------------------------------------------------------------*/
+.macro INTERRUPT_EPILOGUE

- ; -- for interrupts, regs above are auto-saved by h/w in that order --
- ; Now do what ISR prologue does (manually save r12, sp, fp, gp, r25)
+ ; INPUT: r0 has STAT32 of calling context
+ ; INPUT: Z flag set if returning to K mode

- INTERRUPT_PROLOGUE exception
+ ; _SOFT clobbers r10 restored by _HARD hence the order

- PUSHAX erbta
- PUSHAX ecr ; r9 contains ECR, expected by EV_Trap
+ __RESTORE_REGFILE_SOFT
+
+#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
+ __RESTORE_REGFILE_HARD
+ add sp, sp, SZ_PT_REGS - 8
+#else
+ add sp, sp, PT_r0
+#endif

- PUSH r0 ; orig_r0
- ; OUTPUT: r9 has ECR
.endm

/*------------------------------------------------------------------------*/
.macro EXCEPTION_EPILOGUE

; INPUT: r0 has STAT32 of calling context
- btst r0, STATUS_U_BIT ; Z flag set if K, used in INTERRUPT_EPILOGUE
-
- add sp, sp, 8 ; orig_r0/ECR don't need restoring
- POPAX erbta
-
- INTERRUPT_EPILOGUE exception
-
- POP r0
- POP r1
- POP r2
- POP r3
- POP r4
- POP r5
- POP r6
- POP r7
- POP r8
- POP r9
- POP r10
- POP r11
-
- POP blink
- POPAX lp_end
- POPAX lp_start
-
- POP r9
- mov lp_count, r9
-
- add sp, sp, 12 ; skip JLI, LDI, EI
- POPAX eret
- POPAX erstatus
-
- ld.as r9, [sp, -12] ; reload r9 which got clobbered
+
+ btst r0, STATUS_U_BIT ; Z flag set if K, used in restoring SP
+
+ ld r10, [sp, PT_event + 4]
+ sr r10, [erbta]
+
+ LD2 r10, r11, PT_ret
+ sr r10, [eret]
+ sr r11, [erstatus]
+
+ __RESTORE_REGFILE_SOFT
+ __RESTORE_REGFILE_HARD
+
+ add sp, sp, SZ_PT_REGS
.endm

.macro FAKE_RET_FROM_EXCPN
diff --git a/arch/arc/include/asm/linkage.h b/arch/arc/include/asm/linkage.h
index b29f1a9fd6f7..7d90163f716f 100644
--- a/arch/arc/include/asm/linkage.h
+++ b/arch/arc/include/asm/linkage.h
@@ -13,6 +13,24 @@

#ifdef __ASSEMBLY__

+.macro ST2 e, o, off
+#ifdef CONFIG_ARC_HAS_LL64
+ std \e, [sp, \off]
+#else
+ st \e, [sp, \off]
+ st \o, [sp, \off+4]
+#endif
+.endm
+
+.macro LD2 e, o, off
+#ifdef CONFIG_ARC_HAS_LL64
+ ldd \e, [sp, \off]
+#else
+ ld \e, [sp, \off]
+ ld \o, [sp, \off+4]
+#endif
+.endm
+
#define ASM_NL ` /* use '`' to mark new line in macro */

/* annotation for data we want in DCCM - if enabled in .config */
diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c
index ecaf34e9235c..e90dccecfd83 100644
--- a/arch/arc/kernel/asm-offsets.c
+++ b/arch/arc/kernel/asm-offsets.c
@@ -58,7 +58,14 @@ int main(void)
DEFINE(PT_r5, offsetof(struct pt_regs, r5));
DEFINE(PT_r6, offsetof(struct pt_regs, r6));
DEFINE(PT_r7, offsetof(struct pt_regs, r7));
+ DEFINE(PT_r8, offsetof(struct pt_regs, r8));
+ DEFINE(PT_r10, offsetof(struct pt_regs, r10));
+ DEFINE(PT_r26, offsetof(struct pt_regs, r26));
DEFINE(PT_ret, offsetof(struct pt_regs, ret));
+ DEFINE(PT_blink, offsetof(struct pt_regs, blink));
+ DEFINE(PT_lpe, offsetof(struct pt_regs, lp_end));
+ DEFINE(PT_lpc, offsetof(struct pt_regs, lp_count));
+ DEFINE(PT_user_r25, offsetof(struct pt_regs, user_r25));

DEFINE(SZ_CALLEE_REGS, sizeof(struct callee_regs));
DEFINE(SZ_PT_REGS, sizeof(struct pt_regs));
diff --git a/arch/arc/kernel/entry-arcv2.S b/arch/arc/kernel/entry-arcv2.S
index 562089d62d9d..6cbf0ee8a20a 100644
--- a/arch/arc/kernel/entry-arcv2.S
+++ b/arch/arc/kernel/entry-arcv2.S
@@ -70,7 +70,7 @@ reserved:

ENTRY(handle_interrupt)

- INTERRUPT_PROLOGUE irq
+ INTERRUPT_PROLOGUE

# irq control APIs local_irq_save/restore/disable/enable fiddle with
# global interrupt enable bits in STATUS32 (.IE for 1 prio, .E[] for 2 prio)
@@ -226,7 +226,7 @@ debug_marker_l1:
bset.nz r11, r11, AUX_IRQ_ACT_BIT_U ; NZ means U
sr r11, [AUX_IRQ_ACT]

- INTERRUPT_EPILOGUE irq
+ INTERRUPT_EPILOGUE
rtie

;####### Return from Exception / pure kernel mode #######
--
2.7.4

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