Am Montag, 3. September 2018, 18:31:03 CEST schrieb Will Deacon: > On Mon, Sep 03, 2018 at 02:23:17PM +0800, Haibo.Xu wrote: > > Add PTRACE_SYSEMU and PTRACE_SYSEMU_SINGLESTEP support on ARM64. > > This copies the x86 semantics for invoking ptrace hooks, and have > > been verified on ARM64 machine. > > > > Signed-off-by: Haibo.Xu <[email protected]> > > Signed-off-by: Bin.Lu <[email protected]> > > --- > > arch/arm64/include/asm/thread_info.h | 5 ++++- > > arch/arm64/include/uapi/asm/ptrace.h | 2 ++ > > arch/arm64/kernel/ptrace.c | 17 +++++++++++++++++ > > 3 files changed, 23 insertions(+), 1 deletion(-) > > What is PTRACE_SYSEMU and what is its semantics? Why isn't it done in the > core ptrace code?
It is an optimization added for UserModeLinux many years ago. PTRACE_SYSEMU basically allows you to handle system calls in user space without the kernel seeing them. Before that UML had to render every system call into a no-op, e.h. getpid(). This was complicated and slow. The ptrace() manpage has a section on PTRACE_SYSEMU, more documentation on the semantics is not available. And yes, I think this should also done in the core. Like many other ptrace() areas this needs a cleanup. ;-) I wonder what Haibo Xu want to do with PTRACE_SYSEMU on arm64. Are you porting UML or gvisor to arm64? Thanks, //richard
