[9fans] 9syscall

[9fans] 9syscall

[erik quanstrom]

		case amd64
			if(~ $i seek)
				echo TEXT _seek'(SB)', 1, '$0'
			if not
				echo TEXT $i'(SB)', 1, '$0'

why is this necessary?  surely this is artefact?

- erik

Re: [9fans] 9syscall

[cinap_lenrek]

because the kernel assumes that returned vlong is passed
by reference in the first argument, where on amd64, the
(amd64) calling convention returns it in 64 bit AX register.

so seek() is a library func that emulates the previous convention
for _seek() syscall.

--
cinap

Re: [9fans] 9syscall

[erik quanstrom]

On Thu Jun 12 09:35:29 EDT 2014, cinap_lenrek@felloff.net wrote:
> because the kernel assumes that returned vlong is passed
> by reference in the first argument, where on amd64, the
> (amd64) calling convention returns it in 64 bit AX register.
>
> so seek() is a library func that emulates the previous convention
> for _seek() syscall.

that's not how the amd64 kernel has worked.  the registers are 64 bits,
the return value, regardless of where it is is 64 bits.  for example, anything
returning an address would already just work, such as segbrk.

- erik

Re: [9fans] 9syscall

[cinap_lenrek]

yes. what was returned by register keeps being returned by register (segbrk).

--
cinap

Re: [9fans] 9syscall

[erik quanstrom]

On Thu Jun 12 10:12:56 EDT 2014, cinap_lenrek@felloff.net wrote:
> yes. what was returned by register keeps being returned by register (segbrk).

so therefore seek is not special either on amd64.

by the way seek(fd, 0xffffffffull, 0) will always return -1
on the architectures with the sign extension hack.

- erik

Re: [9fans] 9syscall

[cinap_lenrek]

the difference is, returning pointers the natural way works on all archs.
returning vlong works differently depending on the arch. so
the "portable" syscall handlers use a convention that works the
same on all archs, assuming returned vlong is passed by reference.

no doubt, you *could* return it "naturally" on 64bit arch. maybe your 64bit
kernel does, i dont know.

--
cinap

Re: [9fans] 9syscall

[erik quanstrom]

On Thu Jun 12 10:31:30 EDT 2014, cinap_lenrek@felloff.net wrote:
> the difference is, returning pointers the natural way works on all archs.
> returning vlong works differently depending on the arch. so
> the "portable" syscall handlers use a convention that works the
> same on all archs, assuming returned vlong is passed by reference.

is that portable or is that a 32-bit assumption?

- erik