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capstone-engine
Incorrect operands in arm64 "prfm" disassembly
I found this issue when implementing Crabstone Ruby binding on Capstone 5. The existing unit tests failed with Capstone 5.
Work environment
| Questions | Answers |
|---|---|
| OS/arch/bits | Ubuntu x86 64 |
| Architecture | arm64 |
| Source of Capstone | git clone |
| Version/git commit | (v5.0.1, 1bd2a32f2afc6e08225d7491b82619cf4c8e87d9), (next, 4f964a264ec25eb9d468a5495fbd6142778c3a47) |
Instruction bytes giving faulty results
0x40,0x4b,0xa6,0xf8
Expected results
It should be:
Have two operands, one is PREFETCH and one is MEM.
Steps to get the wrong result
With cstool:
On the v5 branch, only one operand is reported:
cstool/cstool -v
cstool for Capstone Disassembler, v5.0.1
Capstone build: x86=1 arm=1 arm64=1 mips=1 ppc=1 sparc=1 sysz=1 xcore=1 m68k=1 tms320c64x=1 m680x=1 evm=1 wasm=1 mos65xx=1 bpf=1 riscv=1 sh=1 tricore=1
cstool/cstool -d arm64 '404ba6f8'
0 40 4b a6 f8 prfm pldl1keep, [x26, w6, uxtw]
ID: 713 (prfm)
op_count: 1
operands[0].type: MEM
operands[0].mem.base: REG = x26
operands[0].mem.index: REG = w6
operands[0].access: READ | WRITE
Ext: 3
Registers read: x26 w6
On the next branch, it reports two operands but the first one doesn't look right, at least it seems reporting mnemonic instead of the operand.
cstool/cstool -d aarch64 '404ba6f8'
0 40 4b a6 f8 prfm pldl1keep, [x26, w6, uxtw]
ID: 782 (prfm)
op_count: 2
operands[0].type: SYS ALIAS:
operands[0].subtype PRFM = 0x0
operands[1].type: MEM
operands[1].mem.base: REG = x26
operands[1].mem.index: REG = w6
operands[1].access: READ
Ext: 3
Registers read: x26 w6
On both Capstone v3 and v4 the output match what I expect:
On v3:
cstool/cstool -d arm64 '404ba6f8'
0 40 4b a6 f8 prfm pldl1keep, [x26, w6, uxtw]
op_count: 2
operands[0].type: PREFETCH = 0x1
operands[1].type: MEM
operands[1].mem.base: REG = x26
operands[1].mem.index: REG = w6
Ext: 3
On v4:
cstool/cstool -d arm64 '404ba6f8'
0 40 4b a6 f8 prfm pldl1keep, [x26, w6, uxtw]
ID: 204 (prfm)
op_count: 2
operands[0].type: PREFETCH = 0x1
operands[1].type: MEM
operands[1].mem.base: REG = x26
operands[1].mem.index: REG = w6
operands[1].access: READ | WRITE
Ext: 3
Registers read: x26 w6
I am fine with the behavior on the next branch if the output there is expected. In this case this bug only happens on the v5 branch.
On the next branch it shows the enumeration value.
In this case it is AARCH64_PRFM_PLDL1KEEP = 0x0.
See aarch64_prfm what the others are.
v5 is broken, yes.
I found this issue when implementing Crabstone Ruby binding on Capstone 5. The existing unit tests failed with Capstone 5.
I am currently rebuild testing. If you want to add support for newer versions, add support only for future v6 (the current next branch, release set to September). It is way way more up to data and modernized. If you continue, consider rebasing on https://github.com/capstone-engine/capstone/pull/2384. You can consume the yaml files with test cases there. Way way more easier.