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/* entry.S - exception handler for emulating MIPS16 'entry' and 'exit'
pseudo-instructions. These instructions are generated by the compiler
when the -mentry switch is used. The instructions are not implemented
in the MIPS16 CPU; hence the exception handler that emulates them.
This module contains the following public functions:
* void __install_entry_handler(void);
This function installs the entry/exit exception handler. It should
be called before executing any MIPS16 functions that were compiled with
-mentry, typically before main() is called.
* void __remove_entry_handler(void);
This function removes the entry/exit exception handler. It should
be called when the program is exiting, or when it is known that no
more MIPS16 functions compiled with -mentry will be called.
*/
#ifdef __mips16
/* This file contains 32 bit assembly code. */
.set nomips16
#endif
#include "regs.S"
#define CAUSE_EXCMASK 0x3c /* mask for ExcCode in Cause Register */
#define EXC_RI 0x28 /* 101000 == 10 << 2 */
/* Set DEBUG to 1 to enable recording of the last 16 interrupt causes. */
#define DEBUG 0
#if DEBUG
.sdata
int_count:
.space 4 /* interrupt count modulo 16 */
int_cause:
.space 4*16 /* last 16 interrupt causes */
#endif
.text
.set noreorder /* Do NOT reorder instructions */
/* __entry_exit_handler - the reserved instruction exception handler
that emulates the entry and exit instruction. */
__entry_exit_handler:
.set noat /* Do NOT use at register */
#if DEBUG
/* Must avoid using 'la' pseudo-op because it uses gp register, which
may not have a good value in an exception handler. */
# la k0, int_count /* intcount = (intcount + 1) & 0xf */
lui k0 ,%hi(int_count)
addiu k0, k0 ,%lo(int_count)
lw k1, (k0)
addiu k1, k1, 1
andi k1, k1, 0x0f
sw k1, (k0)
# la k0, int_cause /* k1 = &int_cause[intcount] */
lui k0, %hi(int_cause)
addiu k0, k0, %lo(int_cause)
sll k1, k1, 2
add k1, k1, k0
#endif
mfc0 k0, C0_CAUSE /* Fetch cause */
#if DEBUG
sw k0, -4(k1) /* Save exception cause in buffer */
#endif
mfc0 k1, C0_EPC /* Check for Reserved Inst. without */
and k0, CAUSE_EXCMASK /* destroying any register */
subu k0, EXC_RI
bne k0, zero, check_others /* Sorry, go do something else */
and k0, k1, 1 /* Check for TR mode (pc.0 = 1) */
beq k0, zero, ri_in_32 /* Sorry, RI in 32-bit mode */
xor k1, 1
/* Since we now are going to emulate or die, we can use all the T-registers */
/* that MIPS16 does not use (at, t0-t8), and we don't have to save them. */
.set at /* Now it's ok to use at again */
#if 0
j leave
rfe
#endif
lhu t0, 0(k1) /* Fetch the offending instruction */
xor t8, k1, 1 /* Prepare t8 for exit */
and t1, t0, 0xf81f /* Check for entry/exit opcode */
bne t1, 0xe809, other_ri
deareg: and t1, t0, 0x0700 /* Isolate the three a-bits */
srl t1, 6 /* Adjust them so x4 is applied */
slt t2, t1, 17 /* See if this is the exit instruction */
beqz t2, doexit
la t2, savea
subu t2, t1
jr t2 /* Jump into the instruction table */
rfe /* We run the rest in user-mode */
/* This is the entry instruction! */
sw a3, 12(sp) /* 4: a0-a3 saved */
sw a2, 8(sp) /* 3: a0-a2 saved */
sw a1, 4(sp) /* 2: a0-a1 saved */
sw a0, 0(sp) /* 1: a0 saved */
savea: /* 0: No arg regs saved */
dera: and t1, t0, 0x0020 /* Isolate the save-ra bit */
move t7, sp /* Temporary SP */
beq t1, zero, desreg
subu sp, 32 /* Default SP adjustment */
sw ra, -4(t7)
subu t7, 4
desreg: and t1, t0, 0x00c0 /* Isolate the two s-bits */
beq t1, zero, leave
subu t1, 0x0040
beq t1, zero, leave /* Only one to save... */
sw s0, -4(t7) /* Do the first one */
sw s1, -8(t7) /* Do the last one */
leave: jr t8 /* Exit to unmodified EPC */
nop /* Urgh - the only nop!! */
doexf0: mtc1 v0,$f0 /* Copy float value */
b doex2
doexf1: mtc1 v1,$f0 /* Copy double value */
mtc1 v0,$f1
b doex2
doexit: slt t2, t1, 21
beq t2, zero, doexf0
slt t2, t1, 25
beq t2, zero, doexf1
doex2: and t1, t0, 0x0020 /* Isolate ra bit */
beq t1, zero, dxsreg /* t1 holds ra-bit */
addu t7, sp, 32 /* Temporary SP */
lw ra, -4(t7)
subu t7, 4
dxsreg: and t1, t0, 0x00c0 /* Isolate the two s-bits */
beq t1, zero, leavex
subu t1, 0x0040
beq t1, zero, leavex /* Only one to save... */
lw s0, -4(t7) /* Do the first one */
lw s1, -8(t7) /* Do the last one */
leavex: jr ra /* Exit to ra */
addu sp, 32 /* Clean up stack pointer */
/* Come here for exceptions we can't handle. */
ri_in_32:
other_ri:
check_others: /* call the previous handler */
la k0,__previous
jr k0
nop
__exception_code:
.set noreorder
la k0, __entry_exit_handler
# lui k0, %hi(exception)
# addiu k0, k0, %lo(exception)
jr k0
nop
.set reorder
__exception_code_end:
.data
__previous:
.space (__exception_code_end - __exception_code)
.text
/* void __install_entry_handler(void)
Install our entry/exit reserved instruction exception handler.
*/
.ent __install_entry_handler
.globl __install_entry_handler
__install_entry_handler:
.set noreorder
mfc0 a0,C0_SR
nop
li a1,SR_BEV
and a1,a1,a0
beq a1,$0,baseaddr
lui a0,0x8000 /* delay slot */
lui a0,0xbfc0
addiu a0,a0,0x0100
baseaddr:
addiu a0,a0,0x080 /* a0 = base vector table address */
li a1,(__exception_code_end - __exception_code)
la a2,__exception_code
la a3,__previous
/* there must be a better way of doing this???? */
copyloop:
lw v0,0(a0)
sw v0,0(a3)
lw v0,0(a2)
sw v0,0(a0)
addiu a0,a0,4
addiu a2,a2,4
addiu a3,a3,4
subu a1,a1,4
bne a1,$0,copyloop
nop
j ra
nop
.set reorder
.end __install_entry_handler
/* void __remove_entry_handler(void);
Remove our entry/exit reserved instruction exception handler.
*/
.ent __remove_entry_handler
.globl __remove_entry_handler
__remove_entry_handler:
.set noreorder
mfc0 a0,C0_SR
nop
li a1,SR_BEV
and a1,a1,a0
beq a1,$0,res_baseaddr
lui a0,0x8000 /* delay slot */
lui a0,0xbfc0
addiu a0,a0,0x0200
res_baseaddr:
addiu a0,a0,0x0180 /* a0 = base vector table address */
li a1,(__exception_code_end - __exception_code)
la a3,__previous
/* there must be a better way of doing this???? */
res_copyloop:
lw v0,0(a3)
sw v0,0(a0)
addiu a0,a0,4
addiu a3,a3,4
subu a1,a1,4
bne a1,$0,res_copyloop
nop
j ra
nop
.set reorder
.end __remove_entry_handler
/* software_init_hook - install entry/exit handler and arrange to have it
removed at exit. This function is called by crt0.S. */
.text
.globl software_init_hook
.ent software_init_hook
software_init_hook:
.set noreorder
subu sp, sp, 8 /* allocate stack space */
sw ra, 4(sp) /* save return address */
jal __install_entry_handler /* install entry/exit handler */
nop
lui a0, %hi(__remove_entry_handler) /* arrange for exit to */
jal atexit /* de-install handler */
addiu a0, a0, %lo(__remove_entry_handler) /* delay slot */
lw ra, 4(sp) /* get return address */
j ra /* return */
addu sp, sp, 8 /* deallocate stack */
.set reorder
.end software_init_hook
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