As far as I can see, almost all callers of unrecoverable_exception() expect it
to never return.
Can we mark it __noreturn ?
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
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
