On Mon, 8 Apr 2024, Florian Weimer via Gcc wrote:
> * Matheus Afonso Martins Moreira via Gcc:
>
> > + It's stable
> >
> > This is one of the things which makes Linux unique
> > in the operating system landscape: applications
> > can target the kernel directly. Unlike in virtually
> > every other operating system out there, the Linux kernel
> > to user space binary interface is documented[2] as stable.
> > Breaking it is considered a regression in the kernel.
> > Therefore it makes sense for a compiler to target it.
> > The same is not true for any other operating system.
>
> There is quite a bit of variance in how the kernel is entered. On
> x86-64, one once popular mechanism is longer present in widely-used
> kernels.
I assume you're implicitly referencing the vsyscall mechanism, but on
amd64 it's not useful to *enter the kernel*, right? It was useful for
obtaining the result of certain syscalls without actually entering
the kernel, like with vdso.
Unlike i386, where the vdso (as well as vsyscall I guess) provides
the __kernel_vsyscall entrypoint, which provides whichever of
{ int 0x80, sysenter, syscall } methods is available and fastest.
Or am I missing something?
Alexander
