[TUHS] ed.c on Unix v5

Random832 random832 at fastmail.com
Sun Dec 20 00:57:32 AEST 2015

Mark Longridge <cubexyz at gmail.com> writes:

>>> I trimmed the source a bit, there's a function at the
>>> end called getpid()  which is commented out.
>> If your V5 has getpid(), then it's a...  strange version...
> I went back to the original uv5swre.zip file which was what I started
> with and had another look to be sure.
> It's not listed on tuhs under v5 but if one looks at /lib/libc.a via
> 'ar t getpid.o' you can see the object file getpid.o

Plus, you know, the syscall itself.

There are four (well, five with ctime) objects in libc.a with no
matching source file in /usr/source/s4: alloc, getpid, ladd, and
snstat.  Also, mon and qsort have assembly versions in s3 and C
versions in s4, and ctime is in s3 despite the fact that almost
every other libc file is in s4.

jnc at mercury.lcs.mit.edu (Noel Chiappa)

>     > From: Mark Longridge <cubexyz at gmail.com>
>     > if one looks at /lib/libc.a via 'ar t getpid.o' you can see the object
>     > file getpid.o
> Library, schlibrary! The important question is 'is it in the kernel source'?
> (Although now that I think about it, if the library routine tries to use a
> non-existent system call, it should return an error. It would be interested
> to disassemble the library routine, and see what it thinks it is doing.)

getpid.o consists of two instructions: sys getpid; rts pc. So it
unconditionally returns whatever the syscall puts in r0.

Non-existent syscalls map to nosys, which sets u_error to 100
(so, in principle, it will return 100, but), which causes the
process to be sent a signal SIGSYS.

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