* Alexander Monakov: > 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.
The implementation performed a standard system call if a pure userspace implementation wasn't possible. It wasn't intended as a general-purpose way to enter the kernel (although it could be used as such, hence the desire to remove it in some cases). Thanks, Florian
