Re: [09/36] AArch64: Exception handling
From: Christopher Covington <hidden>
Date: 2012-08-09 17:05:40
Hi Catalin and Will, On 01/-10/-28163 02:59 PM, Catalin Marinas wrote:
The patch contains the exception entry code (kernel/entry.S), pt_regs structure and related accessors, undefined instruction trapping and stack tracing. AArch64 Linux kernel (including kernel threads) runs in EL1 mode using the SP1 stack. The vectors don't have a fixed address, only alignment (2^11) requirements.
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quoted hunk ↗ jump to hunk
diff --git a/arch/aarch64/kernel/entry.S b/arch/aarch64/kernel/entry.S new file mode 100644 index 0000000..8ad3995 --- /dev/null +++ b/arch/aarch64/kernel/entry.S@@ -0,0 +1,696 @@ +/* + * Low-level exception handling code
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+/* + * Exception vectors. + */ + .macro ventry label + .align 7 + b \label + .endm + + .align 11 +ENTRY(vectors) + ventry el1_sync_invalid // Synchronous EL1t + ventry el1_irq_invalid // IRQ EL1t + ventry el1_fiq_invalid // FIQ EL1t + ventry el1_error_invalid // Error EL1t + + ventry el1_sync // Synchronous EL1h + ventry el1_irq // IRQ EL1h + ventry el1_fiq_invalid // FIQ EL1h + ventry el1_error_invalid // Error EL1h + + ventry el0_sync // Synchronous 64-bit EL0 + ventry el0_irq // IRQ 64-bit EL0 + ventry el0_fiq_invalid // FIQ 64-bit EL0 + ventry el0_error_invalid // Error 64-bit EL0 + +#ifdef CONFIG_AARCH32_EMULATION + ventry el0_sync_compat // Synchronous 32-bit EL0 + ventry el0_irq_compat // IRQ 32-bit EL0 + ventry el0_fiq_invalid_compat // FIQ 32-bit EL0 + ventry el0_error_invalid_compat // Error 32-bit EL0 +#else + ventry el0_sync_invalid // Synchronous 32-bit EL0 + ventry el0_irq_invalid // IRQ 32-bit EL0 + ventry el0_fiq_invalid // FIQ 32-bit EL0 + ventry el0_error_invalid // Error 32-bit EL0 +#endif +END(vectors) + +/* + * Invalid mode handlers + */ + .macro inv_entry, el, reason, regsize = 64 + kernel_entry el, \regsize + mov x0, sp + mov x1, #\reason + mrs x2, esr_el1 + b bad_mode + .endm
The code seems to indicate that the invalid mode handlers have different alignment requirements than the valid mode handlers, which puzzles me.
+ +el0_sync_invalid: + inv_entry 0, BAD_SYNC +ENDPROC(el0_sync_invalid)
Plain labels, the ENTRY macro, the END macro and the ENDPROC macro are used variously throughout this file, and I wonder if a greater amount of consistency might be attainable. The description of the ENDPROC macro in include/linux/linkage.h makes me think its use might not be completely warranted in blocks of assembly that don't end with a return instruction.
+el0_irq_invalid: + inv_entry 0, BAD_IRQ +ENDPROC(el0_irq_invalid) + +el0_fiq_invalid: + inv_entry 0, BAD_FIQ +ENDPROC(el0_fiq_invalid) + +el0_error_invalid: + inv_entry 0, BAD_ERROR +ENDPROC(el0_error_invalid) + +#ifdef CONFIG_AARCH32_EMULATION +el0_fiq_invalid_compat: + inv_entry 0, BAD_FIQ, 32 +ENDPROC(el0_fiq_invalid_compat) + +el0_error_invalid_compat: + inv_entry 0, BAD_ERROR, 32 +ENDPROC(el0_error_invalid_compat) +#endif + +el1_sync_invalid: + inv_entry 1, BAD_SYNC +ENDPROC(el1_sync_invalid) + +el1_irq_invalid: + inv_entry 1, BAD_IRQ +ENDPROC(el1_irq_invalid) + +el1_fiq_invalid: + inv_entry 1, BAD_FIQ +ENDPROC(el1_fiq_invalid) + +el1_error_invalid: + inv_entry 1, BAD_ERROR +ENDPROC(el1_error_invalid) + +/* + * EL1 mode handlers. + */ + .align 6 +el1_sync: + kernel_entry 1 + mrs x1, esr_el1 // read the syndrome register + lsr x24, x1, #26 // exception class + cmp x24, #0x25 // data abort in EL1 + b.eq el1_da + cmp x24, #0x18 // configurable trap + b.eq el1_undef + cmp x24, #0x26 // stack alignment exception + b.eq el1_sp_pc + cmp x24, #0x22 // pc alignment exception + b.eq el1_sp_pc + cmp x24, #0x00 // unknown exception in EL1 + b.eq el1_undef + cmp x24, #0x30 // debug exception in EL1 + b.ge el1_dbg + b el1_inv +el1_da: + /* + * Data abort handling + */ + mrs x0, far_el1 + enable_dbg_if_not_stepping x2 + // re-enable interrupts if they were enabled in the aborted context + tbnz x23, #7, 1f // PSR_I_BIT + enable_irq +1: + mov x2, sp // struct pt_regs + bl do_mem_abort + + // disable interrupts before pulling preserved data off the stack + disable_irq + kernel_exit 1 +el1_sp_pc: + /* + *Stack or PC alignment exception handling + */ + mrs x0, far_el1 + mov x1, x25 + mov x2, sp + b do_sp_pc_abort +el1_undef: + /* + *Undefined instruction + */ + mov x0, sp + b do_undefinstr +el1_dbg: + /* + * Debug exception handling + */ + tbz x24, #0, el1_inv // EL1 only + mrs x0, far_el1 + mov x2, sp // struct pt_regs + bl do_debug_exception + + kernel_exit 1 +el1_inv: + // TODO: add support for undefined instructions in kernel mode + mov x0, sp + mov x1, #BAD_SYNC + mrs x2, esr_el1 + b bad_mode +ENDPROC(el1_sync) + + .align 6 +el1_irq: + kernel_entry 1 + enable_dbg_if_not_stepping x0 +#ifdef CONFIG_TRACE_IRQFLAGS + bl trace_hardirqs_off +#endif +#ifdef CONFIG_PREEMPT + get_thread_info tsk + ldr x24, [tsk, #TI_PREEMPT] // get preempt count + add x0, x24, #1 // increment it + str x0, [tsk, #TI_PREEMPT] +#endif + irq_handler +#ifdef CONFIG_PREEMPT + str x24, [tsk, #TI_PREEMPT] // restore preempt count + cbnz x24, 1f // preempt count != 0 + ldr x0, [tsk, #TI_FLAGS] // get flags + tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling? + bl el1_preempt +1: +#endif +#ifdef CONFIG_TRACE_IRQFLAGS + bl trace_hardirqs_on +#endif + kernel_exit 1 +ENDPROC(el1_irq) + +#ifdef CONFIG_PREEMPT +el1_preempt: + mov x24, lr +1: enable_dbg + bl preempt_schedule_irq // irq en/disable is done inside + ldr x0, [tsk, #TI_FLAGS] // get new tasks TI_FLAGS + tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling? + ret x24 +#endif + +/* + * EL0 mode handlers. + */ + .align 6 +el0_sync: + kernel_entry 0 + mrs x25, esr_el1 // read the syndrome register + lsr x24, x25, #26 // exception class + cmp x24, #0x15 // SVC in 64-bit state + b.eq el0_svc + adr lr, ret_from_exception + cmp x24, #0x24 // data abort in EL0 + b.eq el0_da + cmp x24, #0x20 // instruction abort in EL0 + b.eq el0_ia + cmp x24, #0x07 // FP/ASIMD access + b.eq el0_fpsimd_acc + cmp x24, #0x2c // FP/ASIMD exception + b.eq el0_fpsimd_exc + cmp x24, #0x18 // configurable trap + b.eq el0_undef + cmp x24, #0x26 // stack alignment exception + b.eq el0_sp_pc + cmp x24, #0x22 // pc alignment exception + b.eq el0_sp_pc + cmp x24, #0x00 // unknown exception in EL0 + b.eq el0_undef + cmp x24, #0x30 // debug exception in EL0 + b.ge el0_dbg + b el0_inv + +#ifdef CONFIG_AARCH32_EMULATION + .align 6 +el0_sync_compat: + kernel_entry 0, 32 + mrs x25, esr_el1 // read the syndrome register + lsr x24, x25, #26 // exception class + cmp x24, #0x11 // SVC in 32-bit state + b.eq el0_svc_compat + adr lr, ret_from_exception + cmp x24, #0x24 // data abort in EL0 + b.eq el0_da + cmp x24, #0x20 // instruction abort in EL0 + b.eq el0_ia + cmp x24, #0x07 // FP/ASIMD access + b.eq el0_fpsimd_acc + cmp x24, #0x28 // FP/ASIMD exception + b.eq el0_fpsimd_exc + cmp x24, #0x00 // unknown exception in EL0 + b.eq el0_undef + cmp x24, #0x30 // debug exception in EL0 + b.ge el0_dbg + b el0_inv +el0_svc_compat: + /* + * AArch32 syscall handling + */ + adr stbl, compat_sys_call_table // load compat syscall table pointer + uxtw scno, w7 // syscall number in w7 (r7) + mov sc_nr, #__NR_compat_syscalls + b el0_svc_naked + + .align 6 +el0_irq_compat: + kernel_entry 0, 32 + b el0_irq_naked +#endif + +el0_da: + /* + * Data abort handling + */ + mrs x0, far_el1 + disable_step x1 + isb + enable_dbg + // enable interrupts before calling the main handler + enable_irq + mov x1, x25 + mov x2, sp + b do_mem_abort +el0_ia: + /* + * Instruction abort handling + */ + mrs x0, far_el1 + disable_step x1 + isb + enable_dbg + // enable interrupts before calling the main handler + enable_irq + orr x1, x25, #1 << 24 // use reserved ISS bit for instruction aborts + mov x2, sp + b do_mem_abort +el0_fpsimd_acc: + /* + * Floating Point or Advanced SIMD access + */ + mov x0, x25 + mov x1, sp + b do_fpsimd_acc +el0_fpsimd_exc: + /* + * Floating Point or Advanced SIMD exception + */ + mov x0, x25 + mov x1, sp + b do_fpsimd_exc +el0_sp_pc: + /* + * Stack or PC alignment exception handling + */ + mrs x0, far_el1 + disable_step x1 + isb + enable_dbg + // enable interrupts before calling the main handler + enable_irq + mov x1, x25 + mov x2, sp + b do_sp_pc_abort +el0_undef: + /* + *Undefined instruction + */ + mov x0, sp + b do_undefinstr +el0_dbg: + /* + * Debug exception handling + */ + tbnz x24, #0, el0_inv // EL0 only + mrs x0, far_el1 + disable_step x1 + mov x1, x25 + mov x2, sp + b do_debug_exception +el0_inv: + mov x0, sp + mov x1, #BAD_SYNC + mrs x2, esr_el1 + b bad_mode +ENDPROC(el0_sync) + + .align 6 +el0_irq: + kernel_entry 0 +el0_irq_naked: + disable_step x1 + isb + enable_dbg +#ifdef CONFIG_TRACE_IRQFLAGS + bl trace_hardirqs_off +#endif + get_thread_info tsk +#ifdef CONFIG_PREEMPT + ldr x24, [tsk, #TI_PREEMPT] // get preempt count + add x23, x24, #1 // increment it + str x23, [tsk, #TI_PREEMPT] +#endif + irq_handler +#ifdef CONFIG_PREEMPT + ldr x0, [tsk, #TI_PREEMPT] + str x24, [tsk, #TI_PREEMPT] + cmp x0, x23 + b.eq 1f + mov x1, #0 + str x1, [x1] // BUG
It looks like the error handling here isn't quite complete.
+1: +#endif +#ifdef CONFIG_TRACE_IRQFLAGS + bl trace_hardirqs_on +#endif + b ret_to_user +ENDPROC(el0_irq)
[...] Regards, Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum