From 15ac49b65024f55c4371a53214879a9c77c4fbf9 Mon Sep 17 00:00:00 2001 From: Russell King Date: Mon, 30 Jul 2012 19:42:10 +0100 Subject: ARM: Fix undefined instruction exception handling While trying to get a v3.5 kernel booted on the cubox, I noticed that VFP does not work correctly with VFP bounce handling. This is because of the confusion over 16-bit vs 32-bit instructions, and where PC is supposed to point to. The rule is that FP handlers are entered with regs->ARM_pc pointing at the _next_ instruction to be executed. However, if the exception is not handled, regs->ARM_pc points at the faulting instruction. This is easy for ARM mode, because we know that the next instruction and previous instructions are separated by four bytes. This is not true of Thumb2 though. Since all FP instructions are 32-bit in Thumb2, it makes things easy. We just need to select the appropriate adjustment. Do this by moving the adjustment out of do_undefinstr() into the assembly code, as only the assembly code knows whether it's dealing with a 32-bit or 16-bit instruction. Cc: Acked-by: Will Deacon Signed-off-by: Russell King --- arch/arm/kernel/entry-armv.S | 111 ++++++++++++++++++++++++++++--------------- 1 file changed, 72 insertions(+), 39 deletions(-) (limited to 'arch/arm/kernel/entry-armv.S') diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index 0d1851ca6eb9..0f82098c9bfe 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -244,6 +244,19 @@ svc_preempt: b 1b #endif +__und_fault: + @ Correct the PC such that it is pointing at the instruction + @ which caused the fault. If the faulting instruction was ARM + @ the PC will be pointing at the next instruction, and have to + @ subtract 4. Otherwise, it is Thumb, and the PC will be + @ pointing at the second half of the Thumb instruction. We + @ have to subtract 2. + ldr r2, [r0, #S_PC] + sub r2, r2, r1 + str r2, [r0, #S_PC] + b do_undefinstr +ENDPROC(__und_fault) + .align 5 __und_svc: #ifdef CONFIG_KPROBES @@ -261,25 +274,32 @@ __und_svc: @ @ r0 - instruction @ -#ifndef CONFIG_THUMB2_KERNEL +#ifndef CONFIG_THUMB2_KERNEL ldr r0, [r4, #-4] #else + mov r1, #2 ldrh r0, [r4, #-2] @ Thumb instruction at LR - 2 cmp r0, #0xe800 @ 32-bit instruction if xx >= 0 - ldrhhs r9, [r4] @ bottom 16 bits - orrhs r0, r9, r0, lsl #16 + blo __und_svc_fault + ldrh r9, [r4] @ bottom 16 bits + add r4, r4, #2 + str r4, [sp, #S_PC] + orr r0, r9, r0, lsl #16 #endif - adr r9, BSYM(1f) + adr r9, BSYM(__und_svc_finish) mov r2, r4 bl call_fpe + mov r1, #4 @ PC correction to apply +__und_svc_fault: mov r0, sp @ struct pt_regs *regs - bl do_undefinstr + bl __und_fault @ @ IRQs off again before pulling preserved data off the stack @ -1: disable_irq_notrace +__und_svc_finish: + disable_irq_notrace @ @ restore SPSR and restart the instruction @@ -423,25 +443,33 @@ __und_usr: mov r2, r4 mov r3, r5 + @ r2 = regs->ARM_pc, which is either 2 or 4 bytes ahead of the + @ faulting instruction depending on Thumb mode. + @ r3 = regs->ARM_cpsr @ - @ fall through to the emulation code, which returns using r9 if - @ it has emulated the instruction, or the more conventional lr - @ if we are to treat this as a real undefined instruction - @ - @ r0 - instruction + @ The emulation code returns using r9 if it has emulated the + @ instruction, or the more conventional lr if we are to treat + @ this as a real undefined instruction @ adr r9, BSYM(ret_from_exception) - adr lr, BSYM(__und_usr_unknown) + tst r3, #PSR_T_BIT @ Thumb mode? - itet eq @ explicit IT needed for the 1f label - subeq r4, r2, #4 @ ARM instr at LR - 4 - subne r4, r2, #2 @ Thumb instr at LR - 2 -1: ldreqt r0, [r4] + bne __und_usr_thumb + sub r4, r2, #4 @ ARM instr at LR - 4 +1: ldrt r0, [r4] #ifdef CONFIG_CPU_ENDIAN_BE8 - reveq r0, r0 @ little endian instruction + rev r0, r0 @ little endian instruction #endif - beq call_fpe + @ r0 = 32-bit ARM instruction which caused the exception + @ r2 = PC value for the following instruction (:= regs->ARM_pc) + @ r4 = PC value for the faulting instruction + @ lr = 32-bit undefined instruction function + adr lr, BSYM(__und_usr_fault_32) + b call_fpe + +__und_usr_thumb: @ Thumb instruction + sub r4, r2, #2 @ First half of thumb instr at LR - 2 #if CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7 /* * Thumb-2 instruction handling. Note that because pre-v6 and >= v6 platforms @@ -455,7 +483,7 @@ __und_usr: ldr r5, .LCcpu_architecture ldr r5, [r5] cmp r5, #CPU_ARCH_ARMv7 - blo __und_usr_unknown + blo __und_usr_fault_16 @ 16bit undefined instruction /* * The following code won't get run unless the running CPU really is v7, so * coding round the lack of ldrht on older arches is pointless. Temporarily @@ -463,15 +491,18 @@ __und_usr: */ .arch armv6t2 #endif -2: - ARM( ldrht r5, [r4], #2 ) - THUMB( ldrht r5, [r4] ) - THUMB( add r4, r4, #2 ) +2: ldrht r5, [r4] cmp r5, #0xe800 @ 32bit instruction if xx != 0 - blo __und_usr_unknown -3: ldrht r0, [r4] + blo __und_usr_fault_16 @ 16bit undefined instruction +3: ldrht r0, [r2] add r2, r2, #2 @ r2 is PC + 2, make it PC + 4 + str r2, [sp, #S_PC] @ it's a 2x16bit instr, update orr r0, r0, r5, lsl #16 + adr lr, BSYM(__und_usr_fault_32) + @ r0 = the two 16-bit Thumb instructions which caused the exception + @ r2 = PC value for the following Thumb instruction (:= regs->ARM_pc) + @ r4 = PC value for the first 16-bit Thumb instruction + @ lr = 32bit undefined instruction function #if __LINUX_ARM_ARCH__ < 7 /* If the target arch was overridden, change it back: */ @@ -482,17 +513,13 @@ __und_usr: #endif #endif /* __LINUX_ARM_ARCH__ < 7 */ #else /* !(CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7) */ - b __und_usr_unknown + b __und_usr_fault_16 #endif - UNWIND(.fnend ) + UNWIND(.fnend) ENDPROC(__und_usr) - @ - @ fallthrough to call_fpe - @ - /* - * The out of line fixup for the ldrt above. + * The out of line fixup for the ldrt instructions above. */ .pushsection .fixup, "ax" .align 2 @@ -524,11 +551,12 @@ ENDPROC(__und_usr) * NEON handler code. * * Emulators may wish to make use of the following registers: - * r0 = instruction opcode. - * r2 = PC+4 + * r0 = instruction opcode (32-bit ARM or two 16-bit Thumb) + * r2 = PC value to resume execution after successful emulation * r9 = normal "successful" return address - * r10 = this threads thread_info structure. + * r10 = this threads thread_info structure * lr = unrecognised instruction return address + * IRQs disabled, FIQs enabled. */ @ @ Fall-through from Thumb-2 __und_usr @@ -659,12 +687,17 @@ ENTRY(no_fp) mov pc, lr ENDPROC(no_fp) -__und_usr_unknown: - enable_irq +__und_usr_fault_32: + mov r1, #4 + b 1f +__und_usr_fault_16: + mov r1, #2 +1: enable_irq mov r0, sp adr lr, BSYM(ret_from_exception) - b do_undefinstr -ENDPROC(__und_usr_unknown) + b __und_fault +ENDPROC(__und_usr_fault_32) +ENDPROC(__und_usr_fault_16) .align 5 __pabt_usr: -- cgit v1.2.3