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39 |
lampret |
/* entry.S - exception handler for emulating MIPS16 'entry' and 'exit'
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pseudo-instructions. These instructions are generated by the compiler
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when the -mentry switch is used. The instructions are not implemented
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in the MIPS16 CPU; hence the exception handler that emulates them.
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This module contains the following public functions:
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* void __install_entry_handler(void);
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This function installs the entry/exit exception handler. It should
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be called before executing any MIPS16 functions that were compiled with
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-mentry, typically before main() is called.
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* void __remove_entry_handler(void);
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This function removes the entry/exit exception handler. It should
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be called when the program is exiting, or when it is known that no
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more MIPS16 functions compiled with -mentry will be called.
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*/
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#include "regs.S"
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#define CAUSE_EXCMASK 0x3c /* mask for ExcCode in Cause Register */
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#define EXC_RI 0x28 /* 101000 == 10 << 2 */
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/* Set DEBUG to 1 to enable recording of the last 16 interrupt causes. */
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#define DEBUG 0
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#if DEBUG
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.sdata
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int_count:
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.space 4 /* interrupt count modulo 16 */
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int_cause:
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.space 4*16 /* last 16 interrupt causes */
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#endif
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.text
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.set noreorder /* Do NOT reorder instructions */
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/* __entry_exit_handler - the reserved instruction exception handler
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that emulates the entry and exit instruction. */
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__entry_exit_handler:
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.set noat /* Do NOT use at register */
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#if DEBUG
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/* Must avoid using 'la' pseudo-op because it uses gp register, which
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may not have a good value in an exception handler. */
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# la k0, int_count /* intcount = (intcount + 1) & 0xf */
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lui k0 ,%hi(int_count)
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addiu k0, k0 ,%lo(int_count)
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lw k1, (k0)
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addiu k1, k1, 1
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andi k1, k1, 0x0f
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sw k1, (k0)
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# la k0, int_cause /* k1 = &int_cause[intcount] */
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lui k0, %hi(int_cause)
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addiu k0, k0, %lo(int_cause)
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sll k1, k1, 2
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add k1, k1, k0
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#endif
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mfc0 k0, C0_CAUSE /* Fetch cause */
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#if DEBUG
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sw k0, -4(k1) /* Save exception cause in buffer */
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#endif
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mfc0 k1, C0_EPC /* Check for Reserved Inst. without */
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and k0, CAUSE_EXCMASK /* destroying any register */
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subu k0, EXC_RI
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bne k0, zero, check_others /* Sorry, go do something else */
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and k0, k1, 1 /* Check for TR mode (pc.0 = 1) */
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beq k0, zero, ri_in_32 /* Sorry, RI in 32-bit mode */
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xor k1, 1
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/* Since we now are going to emulate or die, we can use all the T-registers */
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/* that MIPS16 does not use (at, t0-t8), and we don't have to save them. */
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.set at /* Now it's ok to use at again */
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#if 0
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j leave
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rfe
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#endif
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lhu t0, 0(k1) /* Fetch the offending instruction */
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xor t8, k1, 1 /* Prepare t8 for exit */
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and t1, t0, 0xf81f /* Check for entry/exit opcode */
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bne t1, 0xe809, other_ri
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deareg: and t1, t0, 0x0700 /* Isolate the three a-bits */
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srl t1, 6 /* Adjust them so x4 is applied */
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slt t2, t1, 17 /* See if this is the exit instruction */
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beqz t2, doexit
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la t2, savea
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subu t2, t1
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jr t2 /* Jump into the instruction table */
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rfe /* We run the rest in user-mode */
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/* This is the entry instruction! */
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sw a3, 12(sp) /* 4: a0-a3 saved */
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sw a2, 8(sp) /* 3: a0-a2 saved */
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sw a1, 4(sp) /* 2: a0-a1 saved */
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sw a0, 0(sp) /* 1: a0 saved */
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savea: /* 0: No arg regs saved */
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dera: and t1, t0, 0x0020 /* Isolate the save-ra bit */
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move t7, sp /* Temporary SP */
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beq t1, zero, desreg
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subu sp, 32 /* Default SP adjustment */
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sw ra, -4(t7)
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subu t7, 4
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desreg: and t1, t0, 0x00c0 /* Isolate the two s-bits */
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beq t1, zero, leave
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subu t1, 0x0040
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beq t1, zero, leave /* Only one to save... */
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sw s0, -4(t7) /* Do the first one */
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sw s1, -8(t7) /* Do the last one */
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leave: jr t8 /* Exit to unmodified EPC */
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nop /* Urgh - the only nop!! */
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doexf0: mtc1 v0,$f0 /* Copy float value */
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b doex2
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doexf1: mtc1 v1,$f0 /* Copy double value */
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mtc1 v0,$f1
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b doex2
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doexit: slt t2, t1, 21
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beq t2, zero, doexf0
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slt t2, t1, 25
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beq t2, zero, doexf1
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doex2: and t1, t0, 0x0020 /* Isolate ra bit */
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beq t1, zero, dxsreg /* t1 holds ra-bit */
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addu t7, sp, 32 /* Temporary SP */
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lw ra, -4(t7)
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subu t7, 4
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dxsreg: and t1, t0, 0x00c0 /* Isolate the two s-bits */
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beq t1, zero, leavex
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subu t1, 0x0040
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beq t1, zero, leavex /* Only one to save... */
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lw s0, -4(t7) /* Do the first one */
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lw s1, -8(t7) /* Do the last one */
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leavex: jr ra /* Exit to ra */
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addu sp, 32 /* Clean up stack pointer */
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/* Come here for exceptions we can't handle. */
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ri_in_32:
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other_ri:
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check_others: /* call the previous handler */
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la k0,__previous
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jr k0
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nop
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__exception_code:
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.set noreorder
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la k0, __entry_exit_handler
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# lui k0, %hi(exception)
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# addiu k0, k0, %lo(exception)
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jr k0
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nop
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.set reorder
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__exception_code_end:
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.data
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__previous:
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.space (__exception_code_end - __exception_code)
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.text
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/* void __install_entry_handler(void)
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Install our entry/exit reserved instruction exception handler.
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*/
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.ent __install_entry_handler
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.globl __install_entry_handler
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__install_entry_handler:
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.set noreorder
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mfc0 a0,C0_SR
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nop
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li a1,SR_BEV
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and a1,a1,a0
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beq a1,$0,baseaddr
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lui a0,0x8000 /* delay slot */
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lui a0,0xbfc0
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addiu a0,a0,0x0100
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baseaddr:
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addiu a0,a0,0x080 /* a0 = base vector table address */
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li a1,(__exception_code_end - __exception_code)
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la a2,__exception_code
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la a3,__previous
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/* there must be a better way of doing this???? */
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copyloop:
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lw v0,0(a0)
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sw v0,0(a3)
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lw v0,0(a2)
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sw v0,0(a0)
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addiu a0,a0,4
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addiu a2,a2,4
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addiu a3,a3,4
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subu a1,a1,4
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bne a1,$0,copyloop
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nop
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j ra
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nop
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.set reorder
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.end __install_entry_handler
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/* void __remove_entry_handler(void);
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Remove our entry/exit reserved instruction exception handler.
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*/
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.ent __remove_entry_handler
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.globl __remove_entry_handler
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__remove_entry_handler:
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.set noreorder
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mfc0 a0,C0_SR
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nop
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li a1,SR_BEV
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and a1,a1,a0
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beq a1,$0,res_baseaddr
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lui a0,0x8000 /* delay slot */
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lui a0,0xbfc0
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addiu a0,a0,0x0200
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res_baseaddr:
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addiu a0,a0,0x0180 /* a0 = base vector table address */
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li a1,(__exception_code_end - __exception_code)
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la a3,__previous
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/* there must be a better way of doing this???? */
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res_copyloop:
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lw v0,0(a3)
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sw v0,0(a0)
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addiu a0,a0,4
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addiu a3,a3,4
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subu a1,a1,4
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bne a1,$0,res_copyloop
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nop
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j ra
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nop
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.set reorder
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.end __remove_entry_handler
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/* software_init_hook - install entry/exit handler and arrange to have it
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removed at exit. This function is called by crt0.S. */
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.text
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.globl software_init_hook
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.ent software_init_hook
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software_init_hook:
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.set noreorder
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subu sp, sp, 8 /* allocate stack space */
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sw ra, 4(sp) /* save return address */
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jal __install_entry_handler /* install entry/exit handler */
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nop
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lui a0, %hi(__remove_entry_handler) /* arrange for exit to */
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jal atexit /* de-install handler */
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addiu a0, a0, %lo(__remove_entry_handler) /* delay slot */
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lw ra, 4(sp) /* get return address */
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j ra /* return */
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addu sp, sp, 8 /* deallocate stack */
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.set reorder
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.end software_init_hook
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