powerpc Linux scv support and scv system call ABI proposal

[Joseph Myers]

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 at codesourcery.com