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implemented safe stack for access exception handler

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This commit is contained in:
Markus Fröschle
2014-01-13 15:13:29 +00:00
parent a97469a53d
commit 9b099d935c
6 changed files with 111 additions and 69 deletions
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59
sys/exceptions.S
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@@ -391,51 +391,41 @@ reset_vector:
// cannot use the supervisor stack in here. Therefore we first switch to a safe stack
// (RAMBAR0, the processor internal SRAM)
access_exception:
move.w #0x2700,sr // disable interrupt
// no point in disabling interrupts within an exception handler
// move.w #0x2700,sr // disable interrupt
// save current SSP
move.l sp,__SUP_SP // defined in linker script: top of SRAM0
lea __SUP_SP - 4,sp // now we can savely use the stack
move.l d0,-(sp) // ++ vr
move.l a0,-(sp)
// save gcc scratch registers, others will be handled by called function
lea -4*4(sp),sp
movem.l d0-d1/a0-a1,(sp)
move.l __SUP_SP,a0 // original stack frame
move.w (a0),d0 // get format_status word from stack
andi.l #0x0c03,d0 // mask out fault status bits
cmpi.l #0x0401,d0 // TLB miss on opword of instruction fetch?
beq access_exception_mmu // yes
cmpi.l #0x0402,d0 // TLB miss on extension word of instruction fetch?
beq access_exception_mmu // yes
cmpi.l #0x0802,d0 // TLB miss on data write?
beq access_exception_mmu // yes
cmpi.l #0x0c02,d0 // TLB miss on data read, or read-modify-write?
beq access_exception_mmu // yes
move.l __SUP_SP,a0 // original stack pointer
// revert stack trickery
move.l 4(a0),-(sp) // format status word
move.l (a0),-(sp) // program counter at access error
jsr _access_exception
lea 2*4(sp),sp // adjust stack
tst.l d0 // handled?
bne bus_error
movem.l (sp),d0-d1/a0-a1 // restore scratch registers
lea 4*4(sp),sp
move.l (sp)+,a0
move.l (sp)+,d0
move.l __SUP_SP,sp
bra bus_error // everything else is a classic bus error
access_exception_mmu:
move.l MCF_MMU_MMUSR,d0 // did the last fault hit in TLB?
btst #1,d0 // yes, it did. So we already mapped that page
bne bus_error // and this must be a real bus error
move.l MCF_MMU_MMUAR,d0
cmp.l #__FASTRAM_END,d0 // above max User RAM area?
bge bus_error // -> bus error
lea -5*4(sp),sp // save gcc scratch registers
movem.l d0-d1/a0-a2,(sp)
move.l d0,-(sp) // fault address
jsr _mmutr_miss // else we have an MMU TLB miss
addq.l #4,sp
movem.l (sp),d0-d1/a0-a2 // restore gcc scratch registers
lea 5*4(sp),sp
@@ -449,11 +439,16 @@ access_exception_mmu:
rte
bus_error:
// revert stack trickery
move.l (sp)+,a0
move.l (sp)+,d0 // restore register
move.l __SUP_SP,sp // restore original stack
bra std_exc_vec
zero_divide:
move.w #0x2700,sr // disable interrupt
move.l a0,-(a7)
move.l d0,-(a7)
move.l 12(a7),a0 // pc