[U-Boot] [BUG] incorrect crash dump output for thumbs mode

[Heinrich Schuchardt]

>> Hello Marek,
>>
>> please, have a look at arch/arm/lib/interrupts.c.
>>
>> If the processor is in thumbs mode when crashing the output is formatted
>> in a different way than when not in thumbs mode, cf. dump_instr(). Is
>> there something wrong with the thumbs mode detection?
>
> Well, try maybe objdump ?
>
> What is more plausible, that the above completely nonsensical
> disassembly actually works and the CPU triggers undefined instruction --
> or that the CPU is actually in thumb mode (hint: imx6 u-boot builds are
> built in thumb2) and there's a bug in efi_device_path.c ? I think the later.
>
> I think maybe you should slow down and consider this option.
>

On a Wandboard which is also imx I had a look at the output of exceptions:

=> exception unaligned

data abort

pc : [<8f7a2b1a>]          lr : [<8f7ab1b7>]

reloc pc : [<1780cb1a>]    lr : [<178151b7>]

sp : 8ed8c3f8  ip : 8f7a2b15     fp : 00000002

r10: 8f7f81f0  r9 : 8ed95ea8     r8 : 8ed99488

r7 : 8f7ab109  r6 : 00000000     r5 : 8ed8c3f9  r4 : 8f7f6358
r3 : 8ed9948c  r2 : 00000001     r1 : 00000000  r0 : 8f7f6358
Flags: nzCv  IRQs off  FIQs off  Mode SVC_32
Code: 8f7e1907 8f7e191f 8f7e193d f105466d (e9d50501)
Resetting CPU ...

cat u-boot.map

  .text.do_unaligned
                 0x1780cb14        0xe cmd/built-in.o

objdump -S -D cmd/arm/exception.o

00000000 <do_unaligned>:
         /*
          * The LDRD instruction requires the data source to be four
byte aligned
          * even if strict alignment fault checking is disabled in the
system
          * control register.
          */
         asm volatile (
    0:   466d            mov     r5, sp
    2:   f105 0501       add.w   r5, r5, #1
    6:   e9d5 6700       ldrd    r6, r7, [r5]
                 "MOV r5, sp\n"
                 "ADD r5, #1\n"
                 "LDRD r6, r7, [r5]\n");
         return CMD_RET_FAILURE;
}
    a:   2001            movs    r0, #1
    c:   4770            bx      lr

So there is a bug in arch/arm/lib/interrupts.c such that it does not
detect thumb mode and outputs the code arround PC incorrectly.

Macro thumb_mode(regs) returns 0 though the thumbs flag is set:

CPSR: 200001f3
THUMBS_FLAG: 00000020

The reason is that in arch/arm/include/asm/proc-armv/ptrace.h
we are checking non-existent CONFIG_ARM_THUMB. We should check
CONFIG_IS_ENABLED(SYS_THUMB_BUILD).

I will send a patch to correct this. With the patch applied the output
is correct:

=> exception unaligned

data abort

pc : [<8f7a2b52>]          lr : [<8f7ab1ef>]

reloc pc : [<1780cb52>]    lr : [<178151ef>]

sp : 8ed8c3f8  ip : 8f7a2b4d     fp : 00000002

r10: 8f7f8228  r9 : 8ed95ea8     r8 : 8ed99488

r7 : 8f7ab141  r6 : 00000000     r5 : 8ed8c3f9  r4 : 8f7f6390

r3 : 8ed9948c  r2 : 00000001     r1 : 00000000  r0 : 8f7f6390
Flags: nzCv  IRQs off  FIQs off  Mode SVC_32 (T)
Code: 8f7e 466d f105 0501 (e9d5) 6700
Resetting CPU ...

Thanks for rubbing my nose into it.

Regards

Heinrich