hwstub: rewrite exception catching

Since we can catch exceptions like data aborts on read/write, it takes very
little to also catch exceptions in calls. When extending this with the catching
of illegal instructions, the call instruction now becomes much more robust and
also for address and instruction probing. Since we can catch several types of
exception, rename set_data_abort_jmp to set_exception_jmp. At the same time,
simplify the logic in read/write request handlers. Also fix a bug in ARM
jump code: it was using
  stmia r1, {..., pc}
as if pc would get current pc + 8 but this is actually implementation defined
on older ARMs (typically pc + 12) and deprecated on newer ARMs, so rewrite the
code avoid that. The set_exception_jmp() function now also reports the exception
type.

Change-Id: Icd0dd52d2456b361b27c4776be09c3d13528ed93

2 files changed, 30 insertions, 25 deletions

diff --git a/utils/hwstub/stub/asm/arm/system.S b/utils/hwstub/stub/asm/arm/system.S
index df6b5a2e81..41551a8004 100644
--- a/utils/hwstub/stub/asm/arm/system.S
+++ b/utils/hwstub/stub/asm/arm/system.S
@@ -18,32 +18,33 @@
  * KIND, either express or implied.
  *
  ****************************************************************************/
+#include "system.h"
 
 /* Handling of data abort:
  * the code can register a "longjmp" buffer to restore the context in case of
  * fault */
 .data
-data_abort_jmp_ctx_ptr:
+exception_jmp_ctx_ptr:
 /* buffer contains in order: cpsr,r4-r11,sp,lr,pc */
 .skip   48 /* = 4 * (cpsr +  11 registers) */
 
 .text
-/* Prototype: int set_data_abort_jmp()
- * Return: 1 in case of data abort, 0 otherwise */
-.global set_data_abort_jmp
-set_data_abort_jmp:
+/* Prototype: int set_exception_jmp()
+ * Return: !=0 in case of exception, 0 otherwise */
+.global set_exception_jmp
+set_exception_jmp:
     mrs     r2, cpsr
-    ldr     r1, =data_abort_jmp_ctx_ptr
-    mov     r0, #0
-    stmia   r1, {r2,r4-r11,sp,lr,pc} /* see PC note below */
-    bx      lr
-    mov     r0, #1 /* <-- PC points here in stmia */
-    bx      lr
+    ldr     r1, =exception_jmp_ctx_ptr
+    mov     r0, #EXCEPTION_NONE /* nothing to report */
+    stmia   r1!, {r2,r4-r11,sp,lr} /* see PC note below */
+    mov     r3, pc /* see note below */
+    str     r3, [r1] /* store PC */
+    bx      lr   /* <-- PC points here in mov */
 
 .global data_abort_handler
 data_abort_handler:
     /* restore everything from context */
-    ldr     r1, =data_abort_jmp_ctx_ptr
+    ldr     r1, =exception_jmp_ctx_ptr
     /* NOTE: we need to restore sp_sys and lr_sys, for this we need the
      * LDM  Rn, {}^
      * variant, but we cannot restore PC from it because ^ has a different
@@ -54,4 +55,5 @@ data_abort_handler:
      * because we do not save the abort address and we don't use an abort stack */
     ldmia   r1, {r0,r4-r11,sp,lr}^  /* this variant cannot have writeback (r1!) */
     msr     spsr, r0
-    ldmia   r1, {r0,r4-r11,sp,lr,pc}^ /* reload some registers but we don't care */
+    mov     r0, #EXCEPTION_ADDR
+    ldmia   r1, {r1,r4-r11,sp,lr,pc}^ /* reload some registers but we don't care */
diff --git a/utils/hwstub/stub/asm/mips/system.S b/utils/hwstub/stub/asm/mips/system.S
index 2d89bde096..7f619c6edd 100644
--- a/utils/hwstub/stub/asm/mips/system.S
+++ b/utils/hwstub/stub/asm/mips/system.S
@@ -19,23 +19,24 @@
  ****************************************************************************/
 #include "mips.h"
 #include "target-config.h"
+#include "system.h"
 
-/* Handling of data abort:
+/* Handling of exception:
  * the code can register a "longjmp" buffer to restore the context in case of
  * fault */
 .data
-.global data_abort_jmp_ctx_ptr
-data_abort_jmp_ctx_ptr:
+.global exception_jmp_ctx_ptr
+exception_jmp_ctx_ptr:
 /* buffer contains in order: s0-s7, sp, s8, ra */
 .skip   44 /* = 4 * (9 callee saved registers + sp + ra) */
 
 .set noreorder
 .section .icode, "ax", %progbits
-/* Prototype: int set_data_abort_jmp()
+/* Prototype: int set_exception_jmp()
  * Return: 1 in case of data abort, 0 otherwise */
-.global set_data_abort_jmp
-set_data_abort_jmp:
-    la v0,  data_abort_jmp_ctx_ptr
+.global set_exception_jmp
+set_exception_jmp:
+    la v0,  exception_jmp_ctx_ptr
     sw s0,  0(v0)
     sw s1,  4(v0)
     sw s2,  8(v0)
@@ -50,10 +51,12 @@ set_data_abort_jmp:
     jr ra
     move v0, zero
 
-/* restore context on read/write error, performs the interrupt return */
-.global restore_data_abort_jmp
-restore_data_abort_jmp:
-la k1, data_abort_jmp_ctx_ptr
+/* restore context on read/write error, performs the interrupt return
+ * arguments:
+ * a0: exception type (EXCEPTION_*) */
+.global restore_exception_jmp
+restore_exception_jmp:
+    la k1, exception_jmp_ctx_ptr
     lw s0,  0(k1)
     lw s1,  4(k1)
     lw s2,  8(k1)
@@ -73,7 +76,7 @@ la k1, data_abort_jmp_ctx_ptr
 #else
     ehb
 #endif
-    li v0, 1
+    move v0, a0 /* set exception type */
     eret
     nop
 .set reorder