Re: [PATCH] ARM: panic with a message when relocation type is unknown

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Andrey,

On 31/5/19 20:56, Andrey Smirnov wrote:
> On Fri, May 31, 2019 at 2:02 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>>
>> Currently such failures result in a
>>
>>         >00000000 00000000
>>
>>         ### ERROR ### Please RESET the board ###
>>
>> With this patch this now becomes
>>
>>         >00000000 00000000
>>         Unknown relocation type
>>         ### ERROR ### Please RESET the board ###
>>
>> which improves user experience a little bit.
>>
>> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
>> ---
>>  arch/arm/cpu/common.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/cpu/common.c b/arch/arm/cpu/common.c
>> index 821cafbf26c2..3668c5977ca9 100644
>> --- a/arch/arm/cpu/common.c
>> +++ b/arch/arm/cpu/common.c
>> @@ -78,7 +78,7 @@ void relocate_to_current_adr(void)
>>                         putc_ll(' ');
>>                         puthex_ll(rel->r_addend);
>>                         putc_ll('\n');
>> -                       panic("");
>> +                       panic("Unknown relocation type");
>>                 }
>>
>>                 dstart += sizeof(*rel);
>> @@ -108,7 +108,7 @@ void relocate_to_current_adr(void)
>>                         putc_ll(' ');
>>                         puthex_ll(rel->r_offset);
>>                         putc_ll('\n');
>> -                       panic("");
>> +                       panic("Unknown relocation type");
> 
> Looking at this code makes me wonder if calls to panic() are even
> appropriate here. I am not sure there's any guarantee that by the time
> we get to this line relocation for "Unknown relocation type"(or
> original "") string would be processed and panic() would get right
> arguments not to mention all of the functions called as a part of
> panic() and their potential dependencies. Another thing about painc()
> is in PBL it completely ignores passed arguments, so no message will
> be printed there.
> 
> Maybe it'd make sense to go in a different direction and drop calls to
> panic() altogether and replace them with:
> 
> puts_ll(relocation_failed_message());
> hang();
> 
> where relocation_failed_message() on ARM can be something like:
> 
> .section .text.relocation_failed_message
> ENTRY(relocation_failed_message)
> push {lr}
> bl 1f
> .byte 'U, 'n, 'k, 'n, 'o, 'w, 'n, '\ , 'r, 'e, 'l, 'o, 'c, 'a, 't, 'i,
> 'o, 'n, '\ , 't, 'y, 'p, 'e, '\r, '\n, 0x00
> 1:
> mov r0, lr
> /* In case we are in thumb */
> bic r0, r0, #1
> pop {pc}
> ENDPROC(relocation_failed_message)
> 
> to guarantee that it won't depend on relocation? Might be an overkill
> though, so take this with a grain of salt.

In my particular case, the string literal was already being accessed relative
to the program counter. Do you know if GCC can be coerced to always do that?

> 
> Thanks,
> Andrey Smirnov
> 

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