Re: [PATCH] backends: Use PTRACE_GETREGSET for ppc_set_initial_registers_tid

[Mark Wielaard <mark@klomp.org>]

Hi,

On Wed, 2022-02-16 at 15:07 +0100, Mark Wielaard wrote:
> The code in ppc_initreg.c used PTRACE_PEEKUSER to fetch all registers
> one by one. Which is slightly inefficient. It did this because it
> wanted
> things to work on linux 2.6.18 which didn't support PTRACE_GETREGSET.
> 
> PTRACE_GETREGSET was only officially since 2.6.34 (but backported
> to some earlier versions). It seems ok to require a linux kernel that
> supports PTRACE_GETREGSET now. This is much more efficient since it
> takes just one ptrace call instead of 44 calls to fetch each register
> individually.
> 
> For some really old versions we need to include <linux/ptrace.h> to
> get PTRACE_GETREGSET defined. And on ppc64 there is no 32bit version
> of struct pt_regs available, so we define that ourselves and check
> how much data is returned to know whether this is a full pt_regs or
> one for a 32bit process. An alternative would be to use the raw
> iov_base bytes with 64bit or 32bit offset constants to get at the
> registers instead of using a struct with names.
> 
> The code works for inspecting a 32bit process from a 64bit build,
> but not the other way around (the previous code also didn't). This
> could work if we also defined and used a 64bit pt_regs struct on
> ppc32. But it seems a use case that is not really used (it was hard
> enough finding ppc32 setups to test this on).
> 
> Tested against ppc and ppc64 on linux 2.6.32 and glibc 2.12 and
> ppc and ppc64 on linux 3.10.0 with glibc 2.17.

Pushed.

Cheers,

Mark