On Sat, 24 Mar 2018 17:10:47 +0000 "Burton, Ross" <ross.bur...@intel.com> wrote:
> On 24 March 2018 at 12:36, Richard Purdie > <richard.pur...@linuxfoundation.org> wrote: > > I think, at least in principle, pseudo could wrap that and intercept > > this particular syscall, check syscall_number (the numbering having > > its own set of issues) and then only handle the specific problem > > case we have. > > And to make things easier I think we could even just ENOTSUPP > renameat2 in the short term (i.e. for 2.5), before looking at a more > comprehensive intercepting > which could solve the Go issue. In the Go case, we would basically have to do something more like debugger traps. They're not using libc *at all*, and unless something's built with cgo or requires C-type libraries, it's not even going to be dynamically linked. No dynamic linker => LD_PRELOAD is irrelevant. > I filed a bug with coreutils yesterday. "Just intercept syscall()" > they said. If they can describe a mechanism for intercepting syscall that they can guarantee will work across all Linux architectures including possible future architectures not yet in use, I'd love to know what it is. See syscall(2) for some examples of the kinds of things that could be concerns, such as the EABI calling convention. We can sort of hope for the best if we just treat everything as a chain of unsigned longs, but that's really *not* safe, and it should not be expected to work reliably across architectures. Honestly, reading it more closely, I don't think we can actually produce behavior that precisely mimics the behavior of syscall() for generic cases on architectures we currently run on. There's magic like setting values in other registers, clobbering registers, and so on, because *this function does not obey general architecture calling conventions*. And if the wrapper does, the wrapper will break at least some of the expected behaviors, by not behaving the same way. Basically: I don't think we can promise that we will correctly pass through both parameters to syscall() and returns from it in on existing architectures we're actually running on today, for the whole set of possible syscalls. So if we intercept syscall(), at least some previously-valid programs break. -s -- _______________________________________________ Openembedded-core mailing list Openembedded-core@lists.openembedded.org http://lists.openembedded.org/mailman/listinfo/openembedded-core