From: "Ron Natalie" <ron@ronnatalie.com>
To: "TUHS main list" <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] A language question
Date: Wed, 01 Sep 2021 15:59:08 +0000 [thread overview]
Message-ID: <emb7ef3194-1912-4969-9763-7a703eefabc9@alien> (raw)
In-Reply-To: <CAD2gp_TjwJJ9O57cwVAUvy+46-81tgsdPxdfLjbOfRNFTrjRNw@mail.gmail.com>
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I disagree. TRAP according to the processor handbook was intended to be
used for what UNIX calls system calls. EMT was the emulator trap used
to simulate other operating systems on the same hardware. Oddly, for
some reason, all the DEC OSes use EMT instructions for their system
calls. This came in handy when JHU ported BasicPlus from RSTS to UNIX.
That executable could run fine on UNIX because we caught the few EMT
traps that mattered to us and simulated them. The only thing we had to
do other than that was to add a "nostack()" system call that got rid of
the normal UNIX-maintained stack starting at the address space (RSTS
executables like many DEC OSs used a stack that started around 1000).
Many of the UNIX signals come straight from PDP-11 traps: SIGFPE,
SIGIOT, SIGSEGV, SIGBUS, SIGILL, SIGEMT. and those traps invoked those
signals.
FPE - floating point exception
ILL - illegal exception (either unknown opcode or CERTAIN of the
privileged instructions, others were ignored)
BUS - fatal unibus timeout trap. Usually an attempt to access a
memory/unibus address that doesn't respond, or to do word accesses on
odd boundaries.
SEGV - accessing memory not mapped to you
IOT - the IOT instruction
BPT - the BPT instruction
TRAP, EMT - these instructions
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next prev parent reply other threads:[~2021-09-01 16:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 13:23 Richard Salz
2021-09-01 13:28 ` Dan Cross
2021-09-01 13:44 ` Clem Cole
2021-09-01 14:23 ` Paul Winalski
2021-09-01 14:29 ` John Cowan
2021-09-01 15:59 ` Ron Natalie [this message]
2021-09-01 18:09 ` Warner Losh
2021-09-01 18:43 ` John Cowan
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