Robert O'Callahan robert at ocallahan.org
Sun Jan 25 22:19:00 PST 2015

On Fri, Jan 23, 2015 at 6:03 PM, Kyle Huey <me at kylehuey.com> wrote:

> Why is this necessary?

When we resume with a PTRACE_SYSEMU (or PTRACE_SYSEMU_SINGLESTEP) on x86,
and we reach a system call, we get a ptrace trap. We need to exit the
emulated system call before we set the registers from the trace. We do that
by single-stepping in finish_emulated_syscall, but as the comments there
describe, it's not trivial since on x86 singlestepping not only exits the
syscall but also executes the instruction after it.

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