Re: [PATCH] x86: Warn .insn instruction with length > 15 bytes

[Jan Beulich <jbeulich@suse.com>]

On 08.02.2024 05:47, Hongyu Wang wrote:
>>    as_bad() is used to mark errors that result in what we
>>    presume to be a useless object file.  Say, we ignored
>>    something that might have been vital.
>>    ...
>>
>>    as_warn() is used when we have an error from which we
>>    have a plausible error recovery.  eg, masking the top
>>    bits of a constant that is longer than will fit in the
>>    destination.  In this case we will continue to assemble
>>    the source, although we may have made a bad assumption,
>>    and we will produce an object file and return normal exit
>>    status (ie, no error).
>>    ...
>>
>> It's obvious to me that just continuing to assemble the over-long
>> instruction is a "plausible error recovery".  It's even more plausible
>> than "masking the top bits of a constant".  Certainly an object file
>> containing a byte sequence correspending to the overlong instruction is
>> not "useless".
> 
> We have encountered such issue when running APX workloads with SDE.
> The over-long instruction became either illegal or wrong instruction
> when executing the program, then it crashes after long time running.
> This definitely increases much effort for runtime diagnostics.

Well, that's what you get for not paying attention to diagnostics.
They aren't emitted just for fun.

Jan

> As the over-long instruction would actually break the program, say the
> object crashes or returns with abnormal exit status, the default
> should be an error for assembler and we can add an option to lower the
> error to warning.