Excerpts from Christophe Leroy's message of February 11, 2021 2:44 am: > As far as I can see, almost all callers of unrecoverable_exception() expect > it to never return. > > Can we mark it __noreturn ?
I don't see why not, do_exit is noreturn. We could make die() noreturn as well. > > Below is interrupt_exit_kernel_prepare() with then without > unrecoverable_exception() declared as > __noreturn. (CONFIG_PREEMPT_NONE, and with the BUG_ON() removed) > > With the __noreturn added, we get no stack frame on the likely path Nice! Thanks, Nick > > 000003a8 <interrupt_exit_kernel_prepare>: > 3a8: 81 43 00 84 lwz r10,132(r3) > 3ac: 71 4a 00 02 andi. r10,r10,2 > 3b0: 41 82 00 30 beq 3e0 <interrupt_exit_kernel_prepare+0x38> > 3b4: 80 62 00 70 lwz r3,112(r2) > 3b8: 74 63 00 01 andis. r3,r3,1 > 3bc: 40 82 00 34 bne 3f0 <interrupt_exit_kernel_prepare+0x48> > 3c0: 7d 40 00 a6 mfmsr r10 > 3c4: 55 4a 04 5e rlwinm r10,r10,0,17,15 > 3c8: 7d 40 01 24 mtmsr r10 > 3cc: 7d 20 00 a6 mfmsr r9 > 3d0: 55 29 07 fa rlwinm r9,r9,0,31,29 > 3d4: 55 29 04 5e rlwinm r9,r9,0,17,15 > 3d8: 7d 20 01 24 mtmsr r9 > 3dc: 4e 80 00 20 blr > 3e0: 94 21 ff f0 stwu r1,-16(r1) > 3e4: 7c 08 02 a6 mflr r0 > 3e8: 90 01 00 14 stw r0,20(r1) > 3ec: 48 00 00 01 bl 3ec <interrupt_exit_kernel_prepare+0x44> > 3ec: R_PPC_REL24 unrecoverable_exception > 3f0: 38 e2 00 70 addi r7,r2,112 > 3f4: 3d 00 00 01 lis r8,1 > 3f8: 7c c0 38 28 lwarx r6,0,r7 > 3fc: 7c c6 40 78 andc r6,r6,r8 > 400: 7c c0 39 2d stwcx. r6,0,r7 > 404: 40 a2 ff f4 bne 3f8 <interrupt_exit_kernel_prepare+0x50> > 408: 38 60 00 01 li r3,1 > 40c: 4b ff ff b4 b 3c0 <interrupt_exit_kernel_prepare+0x18> > > Without the modification: > > 000003a8 <interrupt_exit_kernel_prepare>: > 3a8: 94 21 ff f0 stwu r1,-16(r1) > 3ac: 93 e1 00 0c stw r31,12(r1) > 3b0: 81 23 00 84 lwz r9,132(r3) > 3b4: 71 29 00 02 andi. r9,r9,2 > 3b8: 41 82 00 38 beq 3f0 <interrupt_exit_kernel_prepare+0x48> > 3bc: 81 22 00 70 lwz r9,112(r2) > 3c0: 75 23 00 01 andis. r3,r9,1 > 3c4: 40 82 00 4c bne 410 <interrupt_exit_kernel_prepare+0x68> > 3c8: 7d 20 00 a6 mfmsr r9 > 3cc: 55 29 04 5e rlwinm r9,r9,0,17,15 > 3d0: 7d 20 01 24 mtmsr r9 > 3d4: 7d 20 00 a6 mfmsr r9 > 3d8: 55 29 07 fa rlwinm r9,r9,0,31,29 > 3dc: 55 29 04 5e rlwinm r9,r9,0,17,15 > 3e0: 7d 20 01 24 mtmsr r9 > 3e4: 83 e1 00 0c lwz r31,12(r1) > 3e8: 38 21 00 10 addi r1,r1,16 > 3ec: 4e 80 00 20 blr > 3f0: 7c 08 02 a6 mflr r0 > 3f4: 90 01 00 14 stw r0,20(r1) > 3f8: 48 00 00 01 bl 3f8 <interrupt_exit_kernel_prepare+0x50> > 3f8: R_PPC_REL24 unrecoverable_exception > 3fc: 81 22 00 70 lwz r9,112(r2) > 400: 80 01 00 14 lwz r0,20(r1) > 404: 75 23 00 01 andis. r3,r9,1 > 408: 7c 08 03 a6 mtlr r0 > 40c: 41 82 ff bc beq 3c8 <interrupt_exit_kernel_prepare+0x20> > 410: 39 02 00 70 addi r8,r2,112 > 414: 3d 20 00 01 lis r9,1 > 418: 7c e0 40 28 lwarx r7,0,r8 > 41c: 7c e7 48 78 andc r7,r7,r9 > 420: 7c e0 41 2d stwcx. r7,0,r8 > 424: 40 a2 ff f4 bne 418 <interrupt_exit_kernel_prepare+0x70> > 428: 38 60 00 01 li r3,1 > 42c: 7d 20 00 a6 mfmsr r9 > 430: 55 29 04 5e rlwinm r9,r9,0,17,15 > 434: 7d 20 01 24 mtmsr r9 > 438: 7d 20 00 a6 mfmsr r9 > 43c: 55 29 07 fa rlwinm r9,r9,0,31,29 > 440: 55 29 04 5e rlwinm r9,r9,0,17,15 > 444: 7d 20 01 24 mtmsr r9 > 448: 83 e1 00 0c lwz r31,12(r1) > 44c: 38 21 00 10 addi r1,r1,16 > 450: 4e 80 00 20 blr >
