The reason why the old vDSOs were written in C using inline assembly was
purely because they were embedded in the C library directly as static
inline functions. This was practical during development, because it
meant you could invoke system calls without any library dependencies.
The vDSO was simply a copy of these functions.
Now that we require the use of the vDSO, there is no longer any need for
embedding them in C code directly. Rewriting them in assembly has the
advantage that they are closer to ideal (less useless branching, less
assumptions about registers remaining unclobbered by the kernel, etc).
They are also easier to build, as they no longer depend on the C type
information for CloudABI.
Obtained from: https://github.com/NuxiNL/cloudabi
CloudABI executables already provide support for passing in vDSOs. This
functionality is used by the emulator for OS X to inject system call
handlers. On FreeBSD, we could use it to optimize calls to
gettimeofday(), etc.
Though I don't have any plans to optimize any system calls right now,
let's go ahead and already pass in a vDSO. This will allow us to
simplify the executables, as the traditional "syscall" shims can be
removed entirely. It also means that we gain more flexibility with
regards to adding and removing system calls.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D7438
In order to make it easier to support CloudABI on ARM64, move out all of
the bits from the AMD64 cloudabi_sysvec.c into a new file
cloudabi_module.c that would otherwise remain identical. This reduces
the AMD64 specific code to just ~160 lines.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D3974
MACHINE_CPUARCH expands to aarch64 for arm64, whereas MACHINE always
corresponds to the directory name under sys/ that contains the sources
for that architecture.
Place all of the machine/pointer size independent code in a kernel
module called 'cloudabi'. All of the 64-bit specific code goes in a
separate module called 'cloudabi64'. The latter is only enabled on
amd64, as it is the only architecture supported.
