Re: [PATCH] powerpc/traps: Declare unrecoverable_exception() as __noreturn
From: Gabriel Paubert <hidden>
Date: 2021-02-11 12:45:04
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On Thu, Feb 11, 2021 at 06:34:43AM +0000, Christophe Leroy wrote:
unrecoverable_exception() is never expected to return, most callers have an infiniteloop in case it returns. Ensure it really never returns by terminating it with a BUG(), and declare it __no_return. It always GCC to really simplify functions calling it. In the exemple below,
s/always/allows ? (Otherwise I can't parse it.)
it avoids the stack frame in the likely fast path and avoids code duplication for the exit.
Indeed, nice code generation improvement.
With this patch: 00000348 <interrupt_exit_kernel_prepare>: 348: 81 43 00 84 lwz r10,132(r3) 34c: 71 48 00 02 andi. r8,r10,2 350: 41 82 00 2c beq 37c <interrupt_exit_kernel_prepare+0x34> 354: 71 4a 40 00 andi. r10,r10,16384 358: 40 82 00 20 bne 378 <interrupt_exit_kernel_prepare+0x30> 35c: 80 62 00 70 lwz r3,112(r2) 360: 74 63 00 01 andis. r3,r3,1 364: 40 82 00 28 bne 38c <interrupt_exit_kernel_prepare+0x44> 368: 7d 40 00 a6 mfmsr r10 36c: 7c 11 13 a6 mtspr 81,r0 370: 7c 12 13 a6 mtspr 82,r0 374: 4e 80 00 20 blr 378: 48 00 00 00 b 378 <interrupt_exit_kernel_prepare+0x30>
Infinite loop (seems to be on test of MSR_PR)? Gabriel
quoted hunk ↗ jump to hunk
37c: 94 21 ff f0 stwu r1,-16(r1) 380: 7c 08 02 a6 mflr r0 384: 90 01 00 14 stw r0,20(r1) 388: 48 00 00 01 bl 388 <interrupt_exit_kernel_prepare+0x40> 388: R_PPC_REL24 unrecoverable_exception 38c: 38 e2 00 70 addi r7,r2,112 390: 3d 00 00 01 lis r8,1 394: 7c c0 38 28 lwarx r6,0,r7 398: 7c c6 40 78 andc r6,r6,r8 39c: 7c c0 39 2d stwcx. r6,0,r7 3a0: 40 a2 ff f4 bne 394 <interrupt_exit_kernel_prepare+0x4c> 3a4: 38 60 00 01 li r3,1 3a8: 4b ff ff c0 b 368 <interrupt_exit_kernel_prepare+0x20> Without this patch: 00000348 <interrupt_exit_kernel_prepare>: 348: 94 21 ff f0 stwu r1,-16(r1) 34c: 93 e1 00 0c stw r31,12(r1) 350: 7c 7f 1b 78 mr r31,r3 354: 81 23 00 84 lwz r9,132(r3) 358: 71 2a 00 02 andi. r10,r9,2 35c: 41 82 00 34 beq 390 <interrupt_exit_kernel_prepare+0x48> 360: 71 29 40 00 andi. r9,r9,16384 364: 40 82 00 28 bne 38c <interrupt_exit_kernel_prepare+0x44> 368: 80 62 00 70 lwz r3,112(r2) 36c: 74 63 00 01 andis. r3,r3,1 370: 40 82 00 3c bne 3ac <interrupt_exit_kernel_prepare+0x64> 374: 7d 20 00 a6 mfmsr r9 378: 7c 11 13 a6 mtspr 81,r0 37c: 7c 12 13 a6 mtspr 82,r0 380: 83 e1 00 0c lwz r31,12(r1) 384: 38 21 00 10 addi r1,r1,16 388: 4e 80 00 20 blr 38c: 48 00 00 00 b 38c <interrupt_exit_kernel_prepare+0x44> 390: 7c 08 02 a6 mflr r0 394: 90 01 00 14 stw r0,20(r1) 398: 48 00 00 01 bl 398 <interrupt_exit_kernel_prepare+0x50> 398: R_PPC_REL24 unrecoverable_exception 39c: 80 01 00 14 lwz r0,20(r1) 3a0: 81 3f 00 84 lwz r9,132(r31) 3a4: 7c 08 03 a6 mtlr r0 3a8: 4b ff ff b8 b 360 <interrupt_exit_kernel_prepare+0x18> 3ac: 39 02 00 70 addi r8,r2,112 3b0: 3d 40 00 01 lis r10,1 3b4: 7c e0 40 28 lwarx r7,0,r8 3b8: 7c e7 50 78 andc r7,r7,r10 3bc: 7c e0 41 2d stwcx. r7,0,r8 3c0: 40 a2 ff f4 bne 3b4 <interrupt_exit_kernel_prepare+0x6c> 3c4: 38 60 00 01 li r3,1 3c8: 4b ff ff ac b 374 <interrupt_exit_kernel_prepare+0x2c> Signed-off-by: Christophe Leroy <redacted> --- arch/powerpc/include/asm/interrupt.h | 2 +- arch/powerpc/kernel/interrupt.c | 1 - arch/powerpc/kernel/traps.c | 2 ++ 3 files changed, 3 insertions(+), 2 deletions(-)diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h index dcff30e3919b..fa8bfb91f8df 100644 --- a/arch/powerpc/include/asm/interrupt.h +++ b/arch/powerpc/include/asm/interrupt.h@@ -411,7 +411,7 @@ DECLARE_INTERRUPT_HANDLER(altivec_assist_exception); DECLARE_INTERRUPT_HANDLER(CacheLockingException); DECLARE_INTERRUPT_HANDLER(SPEFloatingPointException); DECLARE_INTERRUPT_HANDLER(SPEFloatingPointRoundException); -DECLARE_INTERRUPT_HANDLER(unrecoverable_exception); +DECLARE_INTERRUPT_HANDLER(unrecoverable_exception) __noreturn; DECLARE_INTERRUPT_HANDLER(WatchdogException); DECLARE_INTERRUPT_HANDLER(kernel_bad_stack);diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index eca3be36c18c..7e7106641ca9 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c@@ -440,7 +440,6 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned return ret; } -void unrecoverable_exception(struct pt_regs *regs); void preempt_schedule_irq(void); notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsigned long msr)diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index 2afa05ad21c8..1ff776e9e8e3 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c@@ -2173,6 +2173,8 @@ DEFINE_INTERRUPT_HANDLER(unrecoverable_exception) pr_emerg("Unrecoverable exception %lx at %lx (msr=%lx)\n", regs->trap, regs->nip, regs->msr); die("Unrecoverable exception", regs, SIGABRT); + /* die() should not return */ + BUG(); } NOKPROBE_SYMBOL(unrecoverable_exception);-- 2.25.0