RE: [RFC PATCH v1 0/5] nolibc x86-64 string functions

[David Laight]

From: Ammar Faizi
> Sent: 01 September 2023 15:42
...
> > > "    movq    %rdx, %rcx\n"
> > > "    movq    %rdi, %rdx\n"
> > > "    movq    %rdi, %rax\n"
> >
> > You seem to have confused yourself about whether you are using %eax or %edx.
> 
> What do you mean? They're all 64-bit pointers.

%ax, %eax, %rax - what is the difference :-)

> What I know is that the %rdx will be clobbered by "subq %rsi, %rdx"
> below and the %rax should be return value. That's why I copy the %rdi
> twice. memmove() returns the dst pointer. Did I miss something?

I'd forgotten about the (stupid) return value.

I'm pretty sure it is an accident from the original pdp-11
implementation from the days before C had an explicit 'return'
statement.
(The pdp-11 I used ran RSX/11M - so had a Fortran compiler
not a C one.)

	David

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