Messages in this thread | | | From | Ard Biesheuvel <> | Date | Mon, 10 Oct 2022 12:10:24 +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 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.
> + else > + val = (__force unsigned int)cpu_to_le32(val);
and swab32() here
> + } > + > if (!bad) > p += sprintf(p, i == 0 ? "(%0*x) " : "%0*x ", > width, val); > -- > 2.25.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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