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Re: powerpc Linux scv support and scv system call ABI proposal
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: Nicholas Piggin <npiggin at gmail dot com>, <linuxppc-dev at lists dot ozlabs dot org>, <libc-alpha at sourceware dot org>, Tulio Magno Quites Machado Filho <tuliom at linux dot ibm dot com>
- Date: Tue, 28 Jan 2020 22:14:48 +0000
- Subject: Re: powerpc Linux scv support and scv system call ABI proposal
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On Tue, 28 Jan 2020, Florian Weimer wrote:
> I don't think we can save LR in a regular register around the system
> call, explicitly in the inline asm statement, because we still have to
> generate proper unwinding information using CFI directives, something
> that you cannot do from within the asm statement.
What other architectures in glibc have done for code sequences for
syscalls that are problematic for compiler-generated CFI is made the C
syscall macros call separate functions defined in a .S file (see
sysdeps/unix/sysv/linux/arm/libc-do-syscall.S,
sysdeps/unix/sysv/linux/i386/libc-do-syscall.S,
sysdeps/unix/sysv/linux/mips/mips32/mips-syscall[567].S). I don't know if
you can do that in this case and still get the performance benefits of the
new instruction.
--
Joseph S. Myers
joseph@codesourcery.com