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

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>

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 47b4acc..c92bacc 100644 (file)
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -492,11 +492,11 @@ config ARC_KVADDR_SIZE
          kernel-user gutter)
 
 config ARC_CURR_IN_REG
-       bool "Dedicate Register r25 for current_task pointer"
+       bool "cache current task pointer in gp"
        default y
        help
-         This reserved Register R25 to point to Current Task in
-         kernel mode. This saves memory access for each such access
+         This reserves gp register to point to Current Task in
+         kernel mode eliding memory access for each access
 
 
 config ARC_EMUL_UNALIGNED

diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index 329400a..2390dd0 100644 (file)
--- a/arch/arc/Makefile
+++ b/arch/arc/Makefile
@@ -28,14 +28,14 @@ cflags-y                            += $(tune-mcpu-def-y)
 endif
 endif
 
-
 ifdef CONFIG_ARC_CURR_IN_REG
 # For a global register definition, make sure it gets passed to every file
 # We had a customer reported bug where some code built in kernel was NOT using
-# any kernel headers, and missing the r25 global register
+# any kernel headers, and missing the global register
 # Can't do unconditionally because of recursive include issues
 # due to <linux/thread_info.h>
 LINUXINCLUDE   +=  -include $(srctree)/arch/arc/include/asm/current.h
+cflags-y       += -ffixed-gp
 endif
 
 cflags-y                               += -fsection-anchors
@@ -67,7 +67,7 @@ cflags-$(CONFIG_ARC_DW2_UNWIND)               += -fasynchronous-unwind-tables $(cfi)
 # small data is default for elf32 tool-chain. If not usable, disable it
 # This also allows repurposing GP as scratch reg to gcc reg allocator
 disable_small_data := y
-cflags-$(disable_small_data)           += -mno-sdata -fcall-used-gp
+cflags-$(disable_small_data)           += -mno-sdata
 
 cflags-$(CONFIG_CPU_BIG_ENDIAN)                += -mbig-endian
 ldflags-$(CONFIG_CPU_BIG_ENDIAN)       += -EB

diff --git a/arch/arc/include/asm/current.h b/arch/arc/include/asm/current.h
index 9b9bdd3..06be89f 100644 (file)
--- a/arch/arc/include/asm/current.h
+++ b/arch/arc/include/asm/current.h
@@ -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

diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
index 0ff4c06..858742f 100644 (file)
--- a/arch/arc/include/asm/entry-arcv2.h
+++ b/arch/arc/include/asm/entry-arcv2.h
@@ -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
 

diff --git a/arch/arc/include/asm/entry-compact.h b/arch/arc/include/asm/entry-compact.h
index 67ff06e..e3383e1 100644 (file)
--- a/arch/arc/include/asm/entry-compact.h
+++ b/arch/arc/include/asm/entry-compact.h
@@ -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 */

diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 2980bc9..49c2e09 100644 (file)
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -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
+       SAVE_R13_TO_R25
+.endm
 
-       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
-
+/*
+ * 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
 
-/*--------------------------------------------------------------
- * 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
- *-------------------------------------------------------------*/
+/*
+ * save/restore kernel mode callee regs at the time of context switch
+ */
 .macro SAVE_CALLEE_SAVED_KERNEL
-
-       SAVE_R13_TO_R24
-
-#ifdef CONFIG_ARC_CURR_IN_REG
-       sub     sp, sp, 4
-#else
-       PUSH    r25
-#endif
+       SAVE_R13_TO_R25
 .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
- *-------------------------------------------------------------*/
-.macro RESTORE_CALLEE_SAVED_USER
-
-#ifdef CONFIG_ARC_CURR_IN_REG
-       POP     r12
-#else
-       POP     r25
-#endif
-       RESTORE_R24_TO_R13
-
-       ; SP is back to start of pt_regs
-#ifdef CONFIG_ARC_CURR_IN_REG
-       st      r12, [sp, PT_user_r25]
-#endif
+       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

diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index cf90fcd..e9798f4 100644 (file)
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -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  */

diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c
index 0e88403..37324fd 100644 (file)
--- a/arch/arc/kernel/asm-offsets.c
+++ b/arch/arc/kernel/asm-offsets.c
@@ -63,8 +63,6 @@ int main(void)
        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/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
index bf16f77..40d8944 100644 (file)
--- a/arch/arc/kernel/ctx_sw.c
+++ b/arch/arc/kernel/ctx_sw.c
@@ -38,11 +38,7 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
                "st.a    r22, [sp, -4]   \n\t"
                "st.a    r23, [sp, -4]   \n\t"
                "st.a    r24, [sp, -4]   \n\t"
-#ifndef CONFIG_ARC_CURR_IN_REG
                "st.a    r25, [sp, -4]   \n\t"
-#else
-               "sub     sp, sp, 4      \n\t"   /* usual r25 placeholder */
-#endif
 
                /* set ksp of outgoing task in tsk->thread.ksp */
 #if KSP_WORD_OFF <= 255
@@ -58,7 +54,7 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
 
                /*
                 * setup _current_task with incoming tsk.
-                * optionally, set r25 to that as well
+                * optionally, set caching reg to that as well
                 * For SMP extra work to get to &_current_task[cpu]
                 * (open coded SET_CURR_TASK_ON_CPU)
                 */
@@ -72,19 +68,14 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
                "st   %2,  [r24]                \n\t"
 #endif
 #ifdef CONFIG_ARC_CURR_IN_REG
-               "mov r25, %2   \n\t"
+               "mov gp, %2   \n\t"
 #endif
 
                /* get ksp of incoming task from tsk->thread.ksp */
                "ld.as  sp, [%2, %1]   \n\t"
 
                /* start loading it's CALLEE reg file */
-
-#ifndef CONFIG_ARC_CURR_IN_REG
                "ld.ab   r25, [sp, 4]   \n\t"
-#else
-               "add    sp, sp, 4       \n\t"
-#endif
                "ld.ab   r24, [sp, 4]   \n\t"
                "ld.ab   r23, [sp, 4]   \n\t"
                "ld.ab   r22, [sp, 4]   \n\t"

diff --git a/arch/arc/kernel/ctx_sw_asm.S b/arch/arc/kernel/ctx_sw_asm.S
index 02c4614..95cba62 100644 (file)
--- a/arch/arc/kernel/ctx_sw_asm.S
+++ b/arch/arc/kernel/ctx_sw_asm.S
@@ -49,7 +49,7 @@ __switch_to:
        SET_CURR_TASK_ON_CPU  r1, r3
 
        /* reload SP with kernel mode stack pointer in task->thread.ksp */
-       ld.as  sp, [r1, (TASK_THREAD + THREAD_KSP)/4]
+       ld.as  sp, [r1, KSP_WORD_OFF]
 
        /* restore the registers */
        RESTORE_CALLEE_SAVED_KERNEL

diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 54e91df..cd26e0f 100644 (file)
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -210,7 +210,6 @@ trap_with_param:
 
        ; Save callee regs in case gdb wants to have a look
        ; SP will grow up by size of CALLEE Reg-File
-       ; NOTE: clobbers r12
        SAVE_CALLEE_SAVED_USER
 
        ; save location of saved Callee Regs @ thread_struct->pc
@@ -318,7 +317,7 @@ resume_user_mode_begin:
        ;      tracer might call PEEKUSR(CALLEE reg)
        ;
        ; NOTE: SP will grow up by size of CALLEE Reg-File
-       SAVE_CALLEE_SAVED_USER          ; clobbers r12
+       SAVE_CALLEE_SAVED_USER
 
        ; save location of saved Callee Regs @ thread_struct->callee
        GET_CURR_TASK_FIELD_PTR   TASK_THREAD, r10

diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 980b71d..96f5915 100644 (file)
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -162,7 +162,6 @@ asmlinkage void ret_from_fork(void);
  * |      SP        |
  * |    orig_r0     |
  * |    event/ECR   |
- * |    user_r25    |
  * ------------------  <===== END of PAGE
  */
 int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
@@ -243,16 +242,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
         */
        c_callee->r25 = task_thread_info(p)->thr_ptr;
 
-#ifdef CONFIG_ARC_CURR_IN_REG
-       /*
-        * setup usermode thread pointer #2:
-        * however for this special use of r25 in kernel, __switch_to() sets
-        * r25 for kernel needs and only in the final return path is usermode
-        * r25 setup, from pt_regs->user_r25. So set that up as well
-        */
-       c_regs->user_r25 = c_callee->r25;
-#endif
-
        return 0;
 }
 

diff --git a/arch/arc/kernel/ptrace.c b/arch/arc/kernel/ptrace.c
index 2abdcd9..8226df3 100644 (file)
--- a/arch/arc/kernel/ptrace.c
+++ b/arch/arc/kernel/ptrace.c
@@ -47,7 +47,6 @@ static const struct pt_regs_offset regoffset_table[] = {
        REG_OFFSET_NAME(sp),
        REG_OFFSET_NAME(orig_r0),
        REG_OFFSET_NAME(event),
-       REG_OFFSET_NAME(user_r25),
        REG_OFFSET_END,
 };
 
@@ -57,7 +56,6 @@ static const struct pt_regs_offset regoffset_table[] = {
        REG_OFFSET_NAME(orig_r0),
        REG_OFFSET_NAME(event),
        REG_OFFSET_NAME(bta),
-       REG_OFFSET_NAME(user_r25),
        REG_OFFSET_NAME(r26),
        REG_OFFSET_NAME(fp),
        REG_OFFSET_NAME(sp),