arc: Rework default exception handlers for ARC EM and HS

Initially crt0.S used a special function, declared as weak as a default
exception handler in interrupt vector table. To let user override individual
handlers, this function had multiple names - one for each IVT entry, which,
however, was terribly confusing for the debugger and user - because it
wasn't clear which symbol will be used as a function name in debugger.
Defining multiple separate functions - one for each handler, would resolve
the mess, but would increase code size of crt0.o.

To clean this up, this patch defines exception handlers as weak symbols as
well, but those are defined as just symbols, not functions, hence there
would be less confusion over what is what. At the same time, users still can
redefine exception handlers symbol by creating functions with respective
names.

libgloss/
2016-05-24  Anton Kolesov  <Anton.Kolesov@synopsys.com>

	* arc/crt0.S: Convert memory_error and friends to non-function
	  symbols.

1 files changed, 34 insertions, 73 deletions

diff --git a/libgloss/arc/crt0.S b/libgloss/arc/crt0.S
index 99c871f21..1d966c211 100644
--- a/libgloss/arc/crt0.S
+++ b/libgloss/arc/crt0.S
@@ -61,29 +61,40 @@
 #if defined (__ARCEM__) || defined (__ARCHS__)
 	.section .ivt, "a", @progbits
 
-; handler's name,          type,    number,name,   offset in IVT (hex/dec)
-.word   __start           ; exception   0   program entry point  0x0     0
-.word   memory_error      ; exception   1   memory_error         0x4     4
-.word   instruction_error ; exception   2   instruction_error    0x8     8
-.word   EV_MachineCheck   ; exception   3   EV_MachineCheck      0xC     12
-.word   EV_TLBMissI       ; exception   4   EV_TLBMissI          0x10    16
-.word   EV_TLBMissD       ; exception   5   EV_TLBMissD          0x14    20
-.word   EV_ProtV          ; exception   6   EV_ProtV             0x18    24
-.word   EV_PrivilegeV     ; exception   7   EV_PrivilegeV        0x1C    28
-.word   EV_SWI            ; exception   8   EV_SWI               0x20    32
-.word   EV_Trap           ; exception   9   EV_Trap              0x24    36
-.word   EV_Extension      ; exception   10  EV_Extension         0x28    40
-.word   EV_DivZero        ; exception   11  EV_DivZero           0x2C    44
-.word   EV_DCError        ; exception   12  EV_DCError           0x30    48
-.word   EV_Malignedr      ; exception   13  EV_Maligned          0x34    52
-.word   _exit_halt        ; exception   14  unused               0x38    56
-.word   _exit_halt        ; exception   15  unused               0x3C    60
-.word   IRQ_Timer0        ; IRQ         16  Timer 0              0x40    64
-.word   IRQ_Timer1        ; IRQ         17  Timer 1              0x44    68
-.word   IRQ_18            ; IRQ         18                       0x48    72
-.word   IRQ_19            ; IRQ         19                       0x4C    76
-.word   IRQ_20            ; IRQ         20                       0x50    80
-
+; Helper macro to define weak symbols to include into interrupt vector table.
+; User code may define those functions in them, so user function will be
+; referenced in the IVT. By default all handlers point to _exit_halt - so they
+; always cause application halt, because if application causes an exception or
+; interrupt, but doesn't set a handler for it - something is wrong in
+; application. Exception is "start" entry of IVT, which points to __start
+; function.
+#define IVT_ENTRY(name) \
+    .word name `\
+    .weak name `\
+    .set name, _exit_halt
+
+; handler's name,          number, name,       offset in IVT (hex/dec)
+.word __start                ; 0   program entry point  0x0     0
+IVT_ENTRY(memory_error)      ; 1   memory_error         0x4     4
+IVT_ENTRY(instruction_error) ; 2   instruction_error    0x8     8
+IVT_ENTRY(EV_MachineCheck)   ; 3   EV_MachineCheck      0xC     12
+IVT_ENTRY(EV_TLBMissI)       ; 4   EV_TLBMissI          0x10    16
+IVT_ENTRY(EV_TLBMissD)       ; 5   EV_TLBMissD          0x14    20
+IVT_ENTRY(EV_ProtV)          ; 6   EV_ProtV             0x18    24
+IVT_ENTRY(EV_PrivilegeV)     ; 7   EV_PrivilegeV        0x1C    28
+IVT_ENTRY(EV_SWI)            ; 8   EV_SWI               0x20    32
+IVT_ENTRY(EV_Trap)           ; 9   EV_Trap              0x24    36
+IVT_ENTRY(EV_Extension)      ; 10  EV_Extension         0x28    40
+IVT_ENTRY(EV_DivZero)        ; 11  EV_DivZero           0x2C    44
+IVT_ENTRY(EV_DCError)        ; 12  EV_DCError           0x30    48
+IVT_ENTRY(EV_Maligned)       ; 13  EV_Maligned          0x34    52
+IVT_ENTRY(EV_Ex14)           ; 14  unused               0x38    56
+IVT_ENTRY(EV_Ex15)           ; 15  unused               0x3C    60
+IVT_ENTRY(IRQ_Timer0)        ; 16  Timer 0              0x40    64
+IVT_ENTRY(IRQ_Timer1)        ; 17  Timer 1              0x44    68
+IVT_ENTRY(IRQ_18)            ; 18                       0x48    72
+IVT_ENTRY(IRQ_19)            ; 19                       0x4C    76
+IVT_ENTRY(IRQ_20)            ; 20                       0x50    80
 
 	.section .text.__startup, "ax", @progbits
 #else
@@ -196,56 +207,6 @@ __start:
 	; r0 contains exit code
 	j	@exit
 
-#if defined (__ARCEM__) || defined (__ARCHS__)
-; ARCv2 default interrupt routines, defined as weak symbols.
-; Default implementation halts the core.  To conserve code size those symbols
-; share a single implementation, however as a downside debugger and
-; disassembler will not be able to distinguish one from another.
-.weak   memory_error
-.weak   instruction_error
-.weak   EV_MachineCheck
-.weak   EV_TLBMissI
-.weak   EV_TLBMissD
-.weak   EV_ProtV
-.weak   EV_PrivilegeV
-.weak   EV_SWI
-.weak   EV_Trap
-.weak   EV_Extension
-.weak   EV_DivZero
-.weak   EV_DCError
-.weak   EV_Malignedr
-.weak   IRQ_Timer0
-.weak   IRQ_Timer1
-.weak   IRQ_18
-.weak   IRQ_19
-.weak   IRQ_20
-
-.balign 4
-memory_error        :
-instruction_error   :
-EV_MachineCheck     :
-EV_TLBMissI         :
-EV_TLBMissD         :
-EV_ProtV            :
-EV_PrivilegeV       :
-EV_SWI              :
-EV_Trap             :
-EV_Extension        :
-EV_DivZero          :
-EV_DCError          :
-EV_Malignedr        :
-IRQ_Timer0          :
-IRQ_Timer1          :
-IRQ_18              :
-IRQ_19              :
-IRQ_20              :
-.Lloop_halt:
-	flag	0x01
-	nop
-	b	.Lloop_halt
-	nop
-#endif /* __ARCEM__ || __ARCHS__ */
-
 	.section .text._exit_halt,"ax",@progbits
 	.global	 _exit_halt
 	.type	 _exit_halt, @function