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[ARM][Disassembler] Advance IT State when instruction is unknown (#154531)

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When an instruction that the disassembler does not recognize is in an IT
block, we should still advance the IT state otherwise the IT state
spills over into the next recognized instruction, which is incorrect.

We want to avoid disassembly like:
it eq
<unknown> // Often because disassembler has insufficient target info. 
addeq r0,r0,r0 // eq spills over into add.

Fixes #150569
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Peter Smith 2025-08-21 10:14:30 +01:00 committed by GitHub
parent 26d4e56be8
commit bcf09c1bc7
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4
llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
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@ -1264,6 +1264,10 @@ DecodeStatus ARMDisassembler::getThumbInstruction(MCInst &MI, uint64_t &Size,
return Result;
}
// Advance IT state to prevent next instruction inheriting
// the wrong IT state.
if (ITBlock.instrInITBlock())
ITBlock.advanceITState();
Size = 0;
return MCDisassembler::Fail;
}

45
llvm/test/tools/llvm-objdump/ELF/ARM/undefined-in-it.s Normal file
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@ -0,0 +1,45 @@
@RUN: llvm-mc -triple arm-none-eabi -mcpu=cortex-m33 -filetype=obj %s | llvm-objdump -d --mcpu=cortex-m3 - | FileCheck %s
@ Check that instructions that are disassembled as <undefined> within an IT
@ block advance the IT state. This prevents the IT state spilling over into
@ the next instruction.
@ The vldmiaeq instruction is disassembled as <undefined> with
@ -mcpu=cortex-m3 as this does not have a fpu.
.text
.fpu fp-armv8
.thumb
ite eq
vldmiaeq r0!, {s16-s31}
addne r0, r0, r0
add r1, r1, r1
itet eq
vldmiaeq r0!, {s16-s31}
vldmiane r0!, {s16-s31}
vldmiaeq r0!, {s16-s31}
add r0, r0, r0
add r1, r1, r1
add r2, r2, r2
it eq
vldmiaeq r0!, {s16-s31}
it ne
addne r0, r0, r0
@ CHECK: 0: bf0c ite eq
@ CHECK-NEXT: 2: ecb0 8a10 <unknown>
@ CHECK-NEXT: 6: 1800 addne r0, r0, r0
@ CHECK-NEXT: 8: 4409 add r1, r1
@ CHECK-NEXT: a: bf0a itet eq
@ CHECK-NEXT: c: ecb0 8a10 <unknown>
@ CHECK-NEXT: 10: ecb0 8a10 <unknown>
@ CHECK-NEXT: 14: ecb0 8a10 <unknown>
@ CHECK-NEXT: 18: 4400 add r0, r0
@ CHECK-NEXT: 1a: 4409 add r1, r1
@ CHECK-NEXT: 1c: 4412 add r2, r2
@ CHECK-NEXT: 1e: bf08 it eq
@ CHECK-NEXT: 20: ecb0 8a10 <unknown>
@ CHECK-NEXT: 24: bf18 it ne
@ CHECK-NEXT: 26: 1800 addne r0, r0, r0