Fwd: [RFA] Fix for mcore simulator

Jeff Law jeffreyalaw@gmail.com
Wed Oct 11 16:49:11 GMT 2023



On 10/10/23 15:35, Martin Simmons wrote:
>>>>>> On Thu, 5 Oct 2023 10:09:44 -0600, Jeff Law via Gdb said:
>>
>> Of course if the code is supposed to behave the same, then that points
>> to problems elsewhere (assembler, linker, simulator).  Sure enough the
>> mcore simulator was mis-handling the sign extension instructions.  The
>> simulator implementation of sextb is via paired shift-by-24 operations.
>> Similarly the simulator implements sexth via paired shift-by-16 operations.
>>
>> The temporary holding the value was declared as a "long" thus this
>> approach worked fine for hosts with a 32 bit wide long and failed
>> miserably for hosts with a 64 bit wide long.
>>
>> This patch makes the shift count automatically adjust based on the size
>> of the temporary.  It includes a simple test for sextb and sexth.  I
>> have _not_ done a full audit of the mcore simulator for more 32->64 bit
>> issues.
> 
> The use of long seems bogus to me.  Why not just declare tmp as int32_t?
That code likely predates any modernization efforts in gdbsim and 
binutils-gdb as a whole -- it's the old interp style simulator that was 
common in the 90s.

I wouldn't lose any sleep if someone took up that task (modernizing that 
codebase) but my interest in mcore is essentially zero, so it won't be me.

Jeff


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