[RFC][PATCH] ARM: ptrace: remove single-step emulation code

[Will Deacon]

Arnaud,

> > strace works fine with this patch applied and, looking at the
> > sources, it doesn't use the SINGLESTEP request. As for ltrace,
> > it *does* use SINGLESTEP but it can use PTRACE_SYSCALL instead
> > (indeed, it does this for sparc, ia64 and mips). ltrace doesn't
> > have code for checking the ptrace return value so I'd say it's
> > their bug.
> 
> afair, the current way to prevent SINGLESTEP usage in ltrace is to
> modify some #ifdef. So, while I agree that not checking ptrace return
> value is not nice, it has nothing to do with SINGLESTEP removal as this
> call will not get compiled in. What matters is rather to know if things
> are still working once the #ifdef are changed and if they're not,
> finding if it's a bug in ltrace or kernel.

Not true. A PTRACE_SINGLESTEP request will simply return -EIO. Userspace
programs should check the return value anyway because it could fail and
then handle the failure gracefully (in the case of ltrace, by trying a
PTRACE_SYSCALL request). This also means that ltrace is currently broken
on Thumb, where PTRACE_SINGLESTEP will return an error code.

Will