On 10/27/15 04:56 PM, Paul Turner wrote: > This series is a new approach which introduces an alternate ABI that does not > depend on open-coded assembly nor a central 'repository' of rseq sequences. > Sequences may now be inlined and the preparatory[*] work for the sequence can > be written in a higher level language. Very nice, it's definitely much easier to use. > Exactly, for x86_64 this looks like: > movq <failed>, rcx [1] > movq $1f, <commit_instr> [2] > cmpq <start value>, <current value> [3] (start is in rcx) > jnz <failed> (4) > movq <to_write>, (<target>) (5) > 1: movq $0, <commit_instr> > > There has been some related discussion, which I am supportive of, in which > we use fs/gs instead of TLS. This maps naturally to the above and removes > the current requirement for per-thread initialization (this is a good thing!). > > On debugger interactions: > > There are some nice properties about this new style of API which allow it to > actually support safe interactions with a debugger: > a) The event counter is a per-cpu value. This means that we can not advance > it if no threads from the same process execute on that cpu. This > naturally allows basic single step support with thread-isolation. I think this means multiple processes would no longer be able to use per-cpu variables in shared memory, since they would no longer restart with respect to each other? > b) Single-step can be augmented to evalute the ABI without incrementing the > event count. > c) A debugger can also be augmented to evaluate this ABI and push restarts > on the kernel's behalf. > > This is also compatible with David's approach of not single stepping between > 2-4 above. However, I think these are ultimately a little stronger since true > single-stepping and breakpoint support would be available. Which would be > nice to allow actual debugging of sequences. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
