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Re: [PATCH] target/ppc: Ease L=0 requirement on cmp/cmpi/cmpl/cmpli for
Matheus K. Ferst
Re: [PATCH] target/ppc: Ease L=0 requirement on cmp/cmpi/cmpl/cmpli for ppc32
Thu, 15 Jul 2021 11:29:28 -0300
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On 15/07/2021 10:14, BALATON Zoltan wrote:
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On Thu, 15 Jul 2021, email@example.com wrote:
From: Matheus Ferst <firstname.lastname@example.org>
In commit 8f0a4b6a9, we started to require L=0 for ppc32 to match what
The Programming Environments Manual say:
"For 32-bit implementations, the L field must be cleared, otherwise
the instruction form is invalid."
Further digging, however, shown that older CPUs have different behavior
concerning invalid forms. E.g.: 440 and 405 manuals say that:
"Unless otherwise noted, the PPC440 will execute all invalid instruction
forms without causing an Illegal Instruction exception".
While the PowerISA has an arguably more restrictive:
"In general, any attempt to execute an invalid form of an instruction
will either cause the system illegal instruction error handler to be
invoked or yield boundedly undefined results."
Finally, BALATON Zoltan (CC'ed) reported that the stricter behavior
By the way, instead of putting this in the commit message usually a
Reported-by tag is used instead to note who reported the problem but I
don't mind either way, just seems unusual to have it in commit message.
Ah, I forgot the tag... again. I swear I'll get used to email workflow
someday. I can send it again if someone thinks it's better.
Matheus K. Ferst
Instituto de Pesquisas ELDORADO <http://www.eldorado.org.br/>
Analista de Software Júnior
Aviso Legal - Disclaimer <https://www.eldorado.org.br/disclaimer.html>