On Thu, 29 Mar 2018 11:39:00 -0400 (EDT)
Mathieu Desnoyers [off-list ref] wrote:

Enforcing SIGSEGV on syscall entry when nested in a rseq critical section
will not be free both in terms of syscall overhead, and in terms of code
maintenance: we'd need to add those checks into entry.S for each architecture
supported, which pretty much doubles the amount of architecture-specific
code we need to implement for rseq. Currently, all we need is to hook in
signal delivery and wire up the system call numbers.

Why not have the check on syscall exit? Then we could use the ptrace
type mechanism to only go that path when a rseq exists for the program.

-- Steve