wip doc, still not working for SPIKE32

src/arch/riscv/traps.S

@@ -26,92 +26,78 @@
 trap_entry:
 
 #ifdef ENABLE_SMP_SUPPORT
-/* The sscratch contains the stack for the current core */
-  csrrw sp, sscratch, sp
-/* Now we have a valid kernel stack */
-  STORE t0, (-2*REGBYTES)(sp)
-  LOAD  t0, (-1*REGBYTES)(sp)
+  /* We need two things now:
+   *   - the stack pointer for the kernel, which is in SSCRATCH
+   *   - a pointer to a space where to store the thread context
+   */
+  csrrw sp, sscratch, sp        /* swap sp and sscratch to get a kernel stack */
+  STORE tp, (-2*REGBYTES)(sp)   /* sp[-2] = tp/x4 */
+  LOAD  tp, (-1*REGBYTES)(sp)   /* tp = sp[-1] */
+  STORE ra, (0*REGBYTES)(tp)    /* t0[0] = ra/x1 */
+  csrrw ra, sscratch, sp        /* sscratch -> ra, sp -> scratch */
+  STORE ra, (1*REGBYTES)(tp)    /* tp[1] = user sp */
+  LOAD  ra, (-2*REGBYTES)(sp)   /* get user tp from sscratch */
 #else
-  csrrw t0, sscratch, t0
-#endif
-  STORE ra, (0*REGBYTES)(t0)
-#ifndef ENABLE_SMP_SUPPORT
-  STORE sp, (1*REGBYTES)(t0)
-#endif
-  STORE gp, (2*REGBYTES)(t0)
-  STORE tp, (3*REGBYTES)(t0)
-  STORE t1, (5*REGBYTES)(t0)
-  STORE t2, (6*REGBYTES)(t0)
-  STORE s0, (7*REGBYTES)(t0)
-  STORE s1, (8*REGBYTES)(t0)
-  STORE a0, (9*REGBYTES)(t0)
-  STORE a1, (10*REGBYTES)(t0)
-  STORE a2, (11*REGBYTES)(t0)
-  STORE a3, (12*REGBYTES)(t0)
-  STORE a4, (13*REGBYTES)(t0)
-  STORE a5, (14*REGBYTES)(t0)
-  STORE a6, (15*REGBYTES)(t0)
-  STORE a7, (16*REGBYTES)(t0)
-  STORE s2, (17*REGBYTES)(t0)
-  STORE s3, (18*REGBYTES)(t0)
-  STORE s4, (19*REGBYTES)(t0)
-  STORE s5, (20*REGBYTES)(t0)
-  STORE s6, (21*REGBYTES)(t0)
-  STORE s7, (22*REGBYTES)(t0)
-  STORE s8, (23*REGBYTES)(t0)
-  STORE s9, (24*REGBYTES)(t0)
-  STORE s10, (25*REGBYTES)(t0)
-  STORE s11, (26*REGBYTES)(t0)
-  STORE t3, (27*REGBYTES)(t0)
-  STORE t4, (28*REGBYTES)(t0)
-  STORE t5, (29*REGBYTES)(t0)
-  STORE t6, (30*REGBYTES)(t0)
-  /* save t0 value */
-#ifdef ENABLE_SMP_SUPPORT
-  LOAD  x1, (-2*REGBYTES)(sp)
-#else
-  csrr  x1, sscratch
+  csrrw tp, sscratch, tp        /* swap tp/x4 and sscratch */
+  STORE ra, (0*REGBYTES)(tp)    /* tp[0] = ra/x1 */
+  STORE sp, (1*REGBYTES)(tp)    /* tp[1] = sp/x2 */
+  la sp, (kernel_stack_alloc + BIT(CONFIG_KERNEL_STACK_BITS))
+  csrr  ra, sscratch            /* ra/x1 = sscratch (t0/x5 of user thread) */
 #endif
-  STORE    x1, (4*REGBYTES)(t0)
-
-  csrr x1, sstatus
-  STORE x1, (32*REGBYTES)(t0)
-
-  csrr s0, scause
-  STORE s0, (31*REGBYTES)(t0)
+  /* x1/ra and x2/sp have already been saved */
+  STORE gp, (2*REGBYTES)(tp)    /* x3 */
+  STORE ra, (3*REGBYTES)(tp)    /* user tp/x4 is in ra/x1 */
+  STORE t0, (4*REGBYTES)(tp)    /* x5 */
+  STORE t1, (5*REGBYTES)(tp)    /* x6 */
+  STORE t2, (6*REGBYTES)(tp)    /* x7 */
+  STORE s0, (7*REGBYTES)(tp)    /* x8 */
+  STORE s1, (8*REGBYTES)(tp)    /* x9 */
+  STORE a0, (9*REGBYTES)(tp)    /* x10 */
+  STORE a1, (10*REGBYTES)(tp)   /* x11*/
+  STORE a2, (11*REGBYTES)(tp)   /* x12 */
+  STORE a3, (12*REGBYTES)(tp)   /* x13 */
+  STORE a4, (13*REGBYTES)(tp)   /* x14 */
+  STORE a5, (14*REGBYTES)(tp)   /* x15 */
+  STORE a6, (15*REGBYTES)(tp)   /* x16 */
+  STORE a7, (16*REGBYTES)(tp)   /* x17 */
+  STORE s2, (17*REGBYTES)(tp)   /* x18 */
+  STORE s3, (18*REGBYTES)(tp)   /* x19 */
+  STORE s4, (19*REGBYTES)(tp)   /* x20 */
+  STORE s5, (20*REGBYTES)(tp)   /* x21 */
+  STORE s6, (21*REGBYTES)(tp)   /* x22 */
+  STORE s7, (22*REGBYTES)(tp)   /* x23 */
+  STORE s8, (23*REGBYTES)(tp)   /* x24 */
+  STORE s9, (24*REGBYTES)(tp)   /* x25 */
+  STORE s10, (25*REGBYTES)(tp)  /* x26 */
+  STORE s11, (26*REGBYTES)(tp)  /* x27 */
+  STORE t3, (27*REGBYTES)(tp)   /* x28 */
+  STORE t4, (28*REGBYTES)(tp)   /* x29 */
+  STORE t5, (29*REGBYTES)(tp)   /* x30 */
+  STORE t6, (30*REGBYTES)(tp)   /* x31 */
+  csrr  t0, scause
+  STORE t0, (31*REGBYTES)(tp)
+  csrr  t1, sstatus
+  STORE t1, (32*REGBYTES)(tp)
+  csrr  t2, sepc
+  STORE t2, (33*REGBYTES)(t0)
 
 .option push
 .option norelax
   la gp, __global_pointer$
 .option pop
 
-#ifdef ENABLE_SMP_SUPPORT
-  /* save the user sp */
-  csrr  x1, sscratch
-  STORE x1, (1*REGBYTES)(t0)
-  /* restore the sscratch */
-  csrw  sscratch, sp
-#else
-  /* Load kernel's stack address */
-  la sp, (kernel_stack_alloc + BIT(CONFIG_KERNEL_STACK_BITS))
-#endif
-
-  /* Save exception PC */
-  csrr x1,  sepc
-  STORE   x1, (33*REGBYTES)(t0)
-
   /* Check if it's an interrupt */
-  bltz s0, interrupt
+  bltz t0, interrupt
 
   /* ratified priv has value 8 for ecall from U-mode exception */
   li   s4, 8
-  bne  s0, s4, exception
+  bne  t0, s4, exception
 
 handle_syscall:
   /* Set the return address to sepc + 4 in the case of a system/environment call */
-  addi x1, x1, 4
+  addi s2, s2, 4
   /* Save NextIP */
-  STORE   x1, (34*REGBYTES)(t0)
+  STORE   s2, (34*REGBYTES)(t0)
 
 #ifdef CONFIG_FASTPATH
   li t3, SYSCALL_CALL
@@ -133,10 +119,10 @@ handle_syscall:
 /* Not an interrupt or a syscall */
 exception:
   /* Save NextIP */
-  STORE   x1, (34*REGBYTES)(t0)
+  STORE  s2, (34*REGBYTES)(t0)
   j c_handle_exception
 
 interrupt:
   /* Save NextIP */
-  STORE   x1, (34*REGBYTES)(t0)
+  STORE   s2, (34*REGBYTES)(t0)
   j c_handle_interrupt