Re: [PATCH 00/17] SME support for AArch64 gdb/gdbserver on Linux.

[Luis Machado <luis.machado@arm.com>]

Hi John,

On 4/11/23 16:50, John Baldwin wrote:
> On 4/10/23 9:26 PM, Luis Machado via Gdb-patches wrote:
>> The following series enables SME 1 (Scalable Matrix Extension) support for
>> AArch64 gdb and gdbserver.
>>
>> SME expands on SVE by having a variable-sized matrix (ZA) of dimensions
>> SVL x SVL bytes.
>>
>> The first few patches and some intermediate ones refactor the code and fix
>> issues prior to enabling SME support, and thus could go in independently.
>>
>> I've kept them in the series as they are closely/logically related.
> 
> I briefly glanced at a few bits of the aarch64-specific parts I'm familiar
> with and they all look fine to me.

Thanks for checking it.

> 
> One note is that I think the AMX patches from Intel (which deal with a
> similar "tile area" split into variable-sized subregisters IIUC) ran into
> some issues with wanting to update the tdesc to deal with the differing
> subregisters since the layout of those can change at runtime.  I'm not
> sure if that applies to SME in the same way and if any of the issues
> Felix ran into might apply to SME as well (and thus if there are common
> solutions?)  (I've cc'd Felix FYI)

I did read Felix's reply, but I'm replying to this thread instead.

I'm not entirely familiar with the AMX spec, though from Felix's descriptions it sounds like there are similarities.

The limitation of gdbserver not being able to properly communicate changes to the vector length to GDB is a known one
for AArch64, as that has been the case since SVE support was put together. I know Thiago is working on it, and SME support
should be fairly simple to adjust to match that design. So I don't see that as a blocker.

For SME we have a new independent vector length (streaming vector length, SVL), so we handle that in the same way as
we handle SVE's vector length (VL). The added complexity comes from the fact we have a new mode called streaming mode.

Whenever that streaming mode is active, then the SVE vectors will use SVL rather than VL for their sizes.

With that said, the new matrix register (ZA) has quite a few subregisters (tiles and tile slices), which I modelled
as pseudo-registers. And yes, they change sizes based on SVL changes.

I addressed that situation by having a separate gdbarch for each VL/SVL set. That means each pseudo-register has its
type cached in the proper gdbarch, so we need to be careful to use the right gdbarch.

I can see there are a few areas of gdb where the code is not totally aware that we can have multiple tdesc's and
gdbarches.

One such example is the gdb core file target XML dump note. That only dumps the process-wide tdesc, but for AArch64
we really need to dump a tdesc for each tdesc.

There might be some corner cases here and there. While implementing SME support I did find some issues that I attempted
to address. For example, the aarch64-linux-specific signal return code having to find out the proper gdbarch as opposed
to just reusing the next frame's gdbarch, which is potentially wrong for SVE/SME.

> 
>> Ezra Sitorus (1):
>>    [binutils/aarch64] sme: Core file support
>>
>> Luis Machado (16):
>>    [gdb/aarch64] Fix register fetch/store order for native AArch64 Linux
>>    [gdb/aarch64] refactor: Rename SVE-specific files
>>    [gdb/gdbserver] refactor: Simplify SVE interface to read/write
>>      registers
>>    [gdb/aarch64] sve: Fix return command when using V registers in a
>>      SVE-enabled target
>>    [gdb/aarch64] sme: Enable SME registers and pseudo-registers
>>    [gdbserver/aarch64] refactor: Adjust expedited registers dynamically
>>    [gdbserver/aarch64] sme: Add support for SME
>>    [gdb/aarch64] sve: Fix signal frame z/v register restore
>>    [gdb/aarch64] sme: Signal frame support
>>    [gdb/aarch64] sme: Fixup sigframe gdbarch when vg/svg changes
>>    [gdb/aarch64] sme: Support TPIDR2 signal frame context
>>    [gdb/generic] corefile/bug: Use thread-specific gdbarch when dumping
>>      register state to core files
>>    [gdb/generic] corefile/bug: Fixup (gcore) core file target description
>>      reading order
>>    [gdb/aarch64] sme: Core file support for Linux
>>    [gdb/testsuite] sme: Add SVE/SME testcases
>>    [gdb/docs] sme: Document SME registers and features
>>
>>   bfd/elf-bfd.h                                 |   4 +
>>   bfd/elf.c                                     |  58 +
>>   gdb/Makefile.in                               |   6 +-
>>   gdb/NEWS                                      |  11 +
>>   gdb/aarch64-linux-nat.c                       | 179 ++--
>>   gdb/aarch64-linux-tdep.c                      | 951 ++++++++++++++---
>>   gdb/aarch64-tdep.c                            | 724 ++++++++++++-
>>   gdb/aarch64-tdep.h                            |  47 +
>>   gdb/arch/aarch64-scalable-linux.c             |  55 +
>>   gdb/arch/aarch64-scalable-linux.h             |  53 +
>>   gdb/arch/aarch64.c                            |   5 +
>>   gdb/arch/aarch64.h                            |  57 +-
>>   gdb/configure.nat                             |   2 +-
>>   gdb/configure.tgt                             |   1 +
>>   gdb/corelow.c                                 |  24 +-
>>   gdb/doc/gdb.texinfo                           |  68 ++
>>   gdb/features/aarch64-sme.c                    |  63 ++
>>   gdb/linux-tdep.c                              |  18 +-
>>   gdb/nat/aarch64-scalable-linux-ptrace.c       | 993 ++++++++++++++++++
>>   gdb/nat/aarch64-scalable-linux-ptrace.h       | 156 +++
>>   ....h => aarch64-scalable-linux-sigcontext.h} |  73 +-
>>   gdb/nat/aarch64-sve-linux-ptrace.c            | 392 -------
>>   gdb/nat/aarch64-sve-linux-ptrace.h            |  72 --
>>   gdb/testsuite/gdb.arch/aarch64-sme-core-0.exp |  18 +
>>   gdb/testsuite/gdb.arch/aarch64-sme-core-1.exp |  18 +
>>   gdb/testsuite/gdb.arch/aarch64-sme-core-2.exp |  18 +
>>   gdb/testsuite/gdb.arch/aarch64-sme-core-3.exp |  18 +
>>   gdb/testsuite/gdb.arch/aarch64-sme-core-4.exp |  18 +
>>   gdb/testsuite/gdb.arch/aarch64-sme-core.c     | 361 +++++++
>>   .../gdb.arch/aarch64-sme-core.exp.tcl         | 167 +++
>>   .../gdb.arch/aarch64-sme-regs-available-0.exp |  18 +
>>   .../gdb.arch/aarch64-sme-regs-available-1.exp |  18 +
>>   .../gdb.arch/aarch64-sme-regs-available-2.exp |  18 +
>>   .../gdb.arch/aarch64-sme-regs-available-3.exp |  18 +
>>   .../gdb.arch/aarch64-sme-regs-available-4.exp |  18 +
>>   .../gdb.arch/aarch64-sme-regs-available.c     | 184 ++++
>>   .../aarch64-sme-regs-available.exp.tcl        | 194 ++++
>>   .../gdb.arch/aarch64-sme-regs-sigframe-0.exp  |  18 +
>>   .../gdb.arch/aarch64-sme-regs-sigframe-1.exp  |  18 +
>>   .../gdb.arch/aarch64-sme-regs-sigframe-2.exp  |  18 +
>>   .../gdb.arch/aarch64-sme-regs-sigframe-3.exp  |  18 +
>>   .../gdb.arch/aarch64-sme-regs-sigframe-4.exp  |  18 +
>>   .../gdb.arch/aarch64-sme-regs-sigframe.c      | 368 +++++++
>>   .../aarch64-sme-regs-sigframe.exp.tcl         | 156 +++
>>   .../aarch64-sme-regs-unavailable-0.exp        |  18 +
>>   .../aarch64-sme-regs-unavailable-1.exp        |  18 +
>>   .../aarch64-sme-regs-unavailable-2.exp        |  18 +
>>   .../aarch64-sme-regs-unavailable-3.exp        |  18 +
>>   .../aarch64-sme-regs-unavailable-4.exp        |  18 +
>>   .../gdb.arch/aarch64-sme-regs-unavailable.c   | 154 +++
>>   .../aarch64-sme-regs-unavailable.exp.tcl      | 162 +++
>>   gdb/testsuite/gdb.arch/aarch64-sme-sanity.c   | 249 +++++
>>   gdb/testsuite/gdb.arch/aarch64-sme-sanity.exp |  72 ++
>>   gdb/testsuite/lib/aarch64.exp                 | 372 +++++++
>>   gdb/testsuite/lib/gdb.exp                     |  63 ++
>>   gdb/tramp-frame.c                             |   1 +
>>   gdb/tramp-frame.h                             |  12 +
>>   gdbserver/Makefile.in                         |   2 +-
>>   gdbserver/configure.srv                       |   3 +-
>>   gdbserver/linux-aarch64-low.cc                | 100 +-
>>   gdbserver/linux-aarch64-tdesc.cc              |  28 +-
>>   gdbserver/server.h                            |   2 +-
>>   62 files changed, 6328 insertions(+), 694 deletions(-)
>>   create mode 100644 gdb/arch/aarch64-scalable-linux.c
>>   create mode 100644 gdb/arch/aarch64-scalable-linux.h
>>   create mode 100644 gdb/features/aarch64-sme.c
>>   create mode 100644 gdb/nat/aarch64-scalable-linux-ptrace.c
>>   create mode 100644 gdb/nat/aarch64-scalable-linux-ptrace.h
>>   rename gdb/nat/{aarch64-sve-linux-sigcontext.h => aarch64-scalable-linux-sigcontext.h} (78%)
>>   delete mode 100644 gdb/nat/aarch64-sve-linux-ptrace.c
>>   delete mode 100644 gdb/nat/aarch64-sve-linux-ptrace.h
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core-0.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core-1.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core-2.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core-3.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core-4.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core.c
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-core.exp.tcl
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available-0.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available-1.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available-2.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available-3.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available-4.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available.c
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-available.exp.tcl
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe-0.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe-1.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe-2.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe-3.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe-4.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe.c
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-sigframe.exp.tcl
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable-0.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable-1.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable-2.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable-3.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable-4.exp
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable.c
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-regs-unavailable.exp.tcl
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-sanity.c
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-sme-sanity.exp
>>   create mode 100644 gdb/testsuite/lib/aarch64.exp
>>
>