Re: [PATCH 0/6] x32: Fast tracepoints support

[Pedro Alves <palves at redhat dot com>]

I almost forgot about this.  I'll push it all to master in
a bit.

I think this is pretty safe to put in 7.12 as well though.
Any thoughts?  Here's my analysis of the patches in the series:

>   x32 Fast tracepoints: IPA target descriptions

This makes './configure && make' just work OOTB on x32.  The IPA
doesn't really work on x32 yet after this, but I think making it
easier for downstreams and users to build gdb trumps someone
trying out fast tracepoints on x32 and that not working.

>   x32 Fast tracepoints: Customize jump pad address

This is guarded under #ifdef so should be quite safe.

>   x32: Avoid unsigned long when installing fast tracepoint jump pads

Trivial and quite safe, IMO.

>   x32: gdbserver's agent bytecode JIT: fix "call" emission
>   x32: gdb: Fix 'call' insn relocation with qRelocInsn

These two fix issues that could trigger with 64-bit as well,
and only touch the code paths that are clearly broken, so safe
to backport, IMO.

>   x32: Fix gdb.trace/mi-trace-frame-collected.exp

This is just a small testsuite tweak that adds a code path
that only executes on x32.

Thanks,
Pedro Alves

On 07/28/2016 02:01 AM, Pedro Alves wrote:
> Yesterday I installed an Ubuntu 16.04 virtual machine here, and
> installed the x32 runtime support (basically, run "apt-cache search
> x32", and install all that shows).  That made it easy to fix a few
> basic x32 problems, the result of which were yesterday's x32 patches.
> 
> There's still one remaining annoying x32 problem however.  Even though
> gdb and gdbserver build fine on x32 now, the build still fails, when
> building the fast tracepoints in-process agent DSO (IPA), with:
> 
>    .../src/gdb/gdbserver/linux-amd64-ipa.c: In function ‘const target_desc* get_ipa_tdesc(int)’:
>    .../src/gdb/gdbserver/linux-amd64-ipa.c:182:14: error: ‘tdesc_amd64_avx_linux’ was not declared in this scope
> 	  return tdesc_amd64_avx_linux;
> 		 ^
>   [...]
> 
> So I took a stab at fixing it.  And then I thought I'd run the fast
> tracepoint tests against the result.  And that showed a few problems,
> all fixed by this series...
> 
> A diff of testing with:
>  RUNTESTFLAGS="--target_board=native-gdbserver" TESTS="gdb.trace/*.exp"
> vs 
>  RUNTESTFLAGS="--target_board=native-gdbserver/-mx32" TESTS="gdb.trace/*.exp"
> 
> Shows that x32 support is just as good as 64-bit.  Actually, it's
> better, since fast tracepoints on shared libraries work.  E.g.:
> 
>  -PASS: gdb.trace/change-loc.exp: 1 ftrace: continue to marker 2 (too far)
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: continue to marker 2
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: tracepoint with three locations
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: continue to marker 3
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: tracepoint with two locations - installed (unload)
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: tracepoint with two locations - pending (unload)
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: tstop
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: tfind frame 0
>  +PASS: gdb.trace/change-loc.exp: 1 ftrace: tfind
> 
> I didn't bother to save a few bytes by making the jump pad,
> gdbserver's agent bytecode JIT etc. use/emit shorter instructions that
> use 32-bit operands in the places where that would be possible on x32.
> Not that it'd be complicated, it's just that I've already invested
> more time in this at this point than I wanted, and that I'm assuming
> that it wouldn't result in a significant optimization.  I'd be glad to
> be proven wrong though, if someone wants to try that out.
> 
> Pedro Alves (6):
>   x32 Fast tracepoints: IPA target descriptions
>   x32 Fast tracepoints: Customize jump pad address
>   x32: Avoid unsigned long when installing fast tracepoint jump pads
>   x32: gdbserver's agent bytecode JIT: fix "call" emission
>   x32: gdb: Fix 'call' insn relocation with qRelocInsn
>   x32: Fix gdb.trace/mi-trace-frame-collected.exp
> 
>  gdb/amd64-tdep.c                                   | 42 ++++++++++--
>  gdb/gdbserver/Makefile.in                          |  9 +++
>  gdb/gdbserver/configure                            | 31 +++++++++
>  gdb/gdbserver/configure.ac                         | 14 ++++
>  gdb/gdbserver/configure.srv                        |  8 ++-
>  gdb/gdbserver/linux-amd64-ipa.c                    | 79 +++++++++++++++++++---
>  gdb/gdbserver/linux-x86-low.c                      |  8 ++-
>  .../gdb.trace/mi-trace-frame-collected.exp         | 14 +++-
>  8 files changed, 186 insertions(+), 19 deletions(-)
>