----- On Jan 31, 2019, at 11:37 AM, Mathieu Desnoyers mathieu.desnoyers@xxxxxxxxxxxx wrote: > ----- On Jan 30, 2019, at 4:10 PM, Joseph Myers joseph@xxxxxxxxxxxxxxxx wrote: > >> On Wed, 30 Jan 2019, Mathieu Desnoyers wrote: >> >>> #if defined (__NR_rseq) && !defined (RSEQ_SIG) >>> # error "UAPI headers support rseq system call, but glibc does not define >>> RSEQ_SIG." >>> #endif >>> >>> Would that take care of your concerns ? >> >> That would of course need appropriate conditionals based on the most >> recent kernel version for which a given glibc version has been updated, so >> that using new kernel headers with an existing glibc release does not make >> the build fail (cf. the test of syscall-names.list). > > The test I hint at above would not be for the glibc build per se. It would > be for a check that glibc implements support for all the system calls > available in the kernel headers (if such a test target currently exists). > >> And being able to >> write such a test only solves one half of the problem - it needs to be >> easy to determine what value to put in that header in glibc for an >> architecture that's newly gained support in the kernel, *without* needing >> any architecture expertise. > > I'm afraid this requirement is incompatible with the nature of the RSEQ > signature. This signature may be required to be a specific trap instruction > by the architecture, so deciding on its value without architecture expertise > is not possible. Just to clarify a point: the "success criterion" I'm aiming for here is to provide a rseq integration that does not cause foreseeable user crashes on upgrade. I'm all for taking into account the maintenance burden on glibc maintainers as a metric in the implementation choices made, but at this point, I don't see how we can achieve success without introducing architecture headers for the RSEQ_SIG signature. If you have ideas on how to further minimize the maintenance burden for glibc maintainers while still meeting the success criterion, I'm all ears. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
