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Subject: Re: [PATCH] compatibility syscall layer (lets try again)
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Daniel Jacobowitz <dan@debian.org>, george anzinger <george@mvista.com>,
       Jim Houston <jim.houston@ccur.com>,
       Stephen Rothwell <sfr@canb.auug.org.au>,
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From: "Martin Schwidefsky" <schwidefsky@de.ibm.com>
Date: Mon, 9 Dec 2002 18:16:43 +0100
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Hi Linus,

>Architecture maintainers, can you comment on how easy/hard it is to do the
>same thing on your architectures? I _assume_ it's trivial (akin to the
>three-liner register state change in i386/kernel/signal.c).

For s390/s390x this is actually quite tricky. The system call number is
coded in the instruction, e.g. 0x0aa2 is svc 162 or sys_nanosleep. There
is no register involved that contains the system call number I could
simply change. I either have to change the instruction (no way) or I
have to avoid going back to userspace in this case. This would require
assembler magic in entry.S. Not nice.

blue skies,
   Martin

Linux/390 Design & Development, IBM Deutschland Entwicklung GmbH
Sch?naicherstr. 220, D-71032 B?blingen, Telefon: 49 - (0)7031 - 16-2247
E-Mail: schwidefsky@de.ibm.com


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