Messages in this thread | | | From | Ard Biesheuvel <> | Date | Mon, 10 Oct 2022 13:07:30 +0200 | Subject | Re: [PATCH v2 2/2] ARM: Make the dumped instructions are consistent with the disassembled ones |
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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?
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