Messages in this thread | | | Subject | Re: [PATCH v2 2/2] ARM: Make the dumped instructions are consistent with the disassembled ones | From | "Leizhen (ThunderTown)" <> | Date | Mon, 10 Oct 2022 19:29:59 +0800 |
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On 2022/10/10 19:07, Ard Biesheuvel wrote: > On Mon, 10 Oct 2022 at 12:46, Leizhen (ThunderTown) > <thunder.leizhen@huawei.com> wrote: >> >> >> >> On 2022/10/10 18:10, Ard Biesheuvel wrote: >>> On Mon, 10 Oct 2022 at 11:56, Zhen Lei <thunder.leizhen@huawei.com> wrote: >>>> >>>> In ARM, the mapping of instruction memory is always little-endian, except >>>> some BE-32 supported ARM architectures. Such as ARMv7-R, its instruction >>>> endianness may be BE-32. Of course, its data endianness will also be BE-32 >>>> mode. Due to two negatives make a positive, the instruction stored in the >>>> register after reading is in little-endian format. But for the case of >>>> BE-8, the instruction endianness is LE, the instruction stored in the >>>> register after reading is in big-endian format, which is inconsistent >>>> with the disassembled one. >>>> >>>> For example: >>>> The content of disassembly: >>>> c0429ee8: e3500000 cmp r0, #0 >>>> c0429eec: 159f2044 ldrne r2, [pc, #68] >>>> c0429ef0: 108f2002 addne r2, pc, r2 >>>> c0429ef4: 1882000a stmne r2, {r1, r3} >>>> c0429ef8: e7f000f0 udf #0 >>>> >>>> The output of undefined instruction exception: >>>> Internal error: Oops - undefined instruction: 0 [#1] SMP ARM >>>> ... ... >>>> Code: 000050e3 44209f15 02208f10 0a008218 (f000f0e7) >>>> >>>> This inconveniences the checking of instructions. What's worse is that, >>>> for somebody who don't know about this, might think the instructions are >>>> all broken. >>>> >>>> So, when CONFIG_CPU_ENDIAN_BE8=y, let's convert the instructions to >>>> little-endian format before they are printed. The conversion result is >>>> as follows: >>>> Code: e3500000 159f2044 108f2002 1882000a (e7f000f0) >>>> >>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >>>> --- >>>> arch/arm/kernel/traps.c | 7 +++++++ >>>> 1 file changed, 7 insertions(+) >>>> >>>> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c >>>> index 34aa80c09c508c1..50b00c9091f079d 100644 >>>> --- a/arch/arm/kernel/traps.c >>>> +++ b/arch/arm/kernel/traps.c >>>> @@ -193,6 +193,13 @@ static void dump_instr(const char *lvl, struct pt_regs *regs) >>>> bad = get_user(val, &((u32 __user *)addr)[i]); >>>> } >>>> >>>> + if (IS_ENABLED(CONFIG_CPU_ENDIAN_BE8)) { >>>> + if (thumb) >>>> + val = (__force unsigned int)cpu_to_le16(val); >>> >>> Better use swab16() here instead of the ugly __force cast, given that >>> the swab is going to occur unconditionally here. >> >> Good idea. >> >>> >>> >>>> + else >>>> + val = (__force unsigned int)cpu_to_le32(val); >>> >>> and swab32() here >> >> OK >> > > Actually, come to think of it, should this code perhaps be using the > mem_to_opcode helpers that are being used elsewhere in the file?
Right, __mem_to_opcode_xxx is the correct solution. I need to test it.
> . >
-- Regards, Zhen Lei
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