Re: [PATCH 00/24] Fix reading and writing pseudo registers in non-current frames

Luis Machado
2023-11-08T17:09:24Z

On 11/8/23 15:47, Simon Marchi wrote:
>> I haven't tracked the particular patch that causes this, but for aarch64 systems supporting SVE
>> (and probably SME as well) I'm seeing internal errors related to one assertion:
> Thanks a lot for testing.
>
>> Running gdb/testsuite/gdb.arch/aarch64-pseudo-unwind.exp ...
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: continue to breakpoint: continue to callee
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: callee, before change: p/x $v8.q.u
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: callee, before change: p/x $s8.u
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: set $s8.u = 0x34353637 (GDB internal error)
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change: p/x $v8.q.u
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change: p/x $s8.u
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: up
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: caller, before change: p/x $v8.q.u
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: caller, before change: p/x $s8.u
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: set $s8.u = 0x44454647 (GDB internal error)
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: caller, after change: p/x $v8.q.u
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: caller, after change: p/x $s8.u
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: down
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change in caller: p/x $v8.q.u
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change in caller: p/x $s8.u
>> PASS: gdb.arch/aarch64-pseudo-unwind.exp: continue to breakpoint: continue to break_here_c
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: p/x value
>> Running gdb/testsuite/gdb.arch/aarch64-fp.exp ...
>> PASS: gdb.arch/aarch64-fp.exp: set the breakpoint after setting the fp registers
>> PASS: gdb.arch/aarch64-fp.exp: continue until breakpoint
>> PASS: gdb.arch/aarch64-fp.exp: check register q0 value
>> PASS: gdb.arch/aarch64-fp.exp: check register q1 value
>> PASS: gdb.arch/aarch64-fp.exp: check register v0 value
>> PASS: gdb.arch/aarch64-fp.exp: check register v1 value
>> PASS: gdb.arch/aarch64-fp.exp: check register fpsr value
>> PASS: gdb.arch/aarch64-fp.exp: check register fpcr value
>> FAIL: gdb.arch/aarch64-fp.exp: bfloat16: set h0.bf to 129 (GDB internal error)
>> FAIL: gdb.arch/aarch64-fp.exp: bfloat16: h0 fields are valid
>> FAIL: gdb.arch/aarch64-fp.exp: bfloat16: set v0.h.bf[0] to 0 (GDB internal error)
>> FAIL: gdb.arch/aarch64-fp.exp: bfloat16: v0.h.s[0] is 0
>> FAIL: gdb.arch/aarch64-fp.exp: bfloat16: set v0.h.bf[0] to 129 (GDB internal error)
>> FAIL: gdb.arch/aarch64-fp.exp: bfloat16: v0.h.s[0] is 129
>>
>> The failure mode is:
>>
>> set $s8.u = 0x34353637^M
>> ../../../repos/binutils-gdb/gdb/frame.c:1441: internal-error: put_frame_register: Assertion `buf.size () == size' failed.^M
>> A problem internal to GDB has been detected,^M
>> further debugging may prove unreliable.^M
>> ----- Backtrace -----^M
>> FAIL: gdb.arch/aarch64-pseudo-unwind.exp: set $s8.u = 0x34353637 (GDB internal error)
>> Resyncing due to internal error.
>> 0xaaaaabd6e08f gdb_internal_backtrace_1^M
>> ../../../repos/binutils-gdb/gdb/bt-utils.c:122^M
>> 0xaaaaabd6e08f _Z22gdb_internal_backtracev^M
>> ../../../repos/binutils-gdb/gdb/bt-utils.c:168^M
>> 0xaaaaac315307 internal_vproblem^M
>> ../../../repos/binutils-gdb/gdb/utils.c:396^M
>> 0xaaaaac31556f _Z15internal_verrorPKciS0_St9__va_list^M
>> ../../../repos/binutils-gdb/gdb/utils.c:476^M
>> 0xaaaaac8604e3 _Z18internal_error_locPKciS0_z^M
>> ../../../repos/binutils-gdb/gdbsupport/errors.cc:58^M
>> 0xaaaaabec89c7 _Z18put_frame_register14frame_info_ptriN3gdb10array_viewIKhEE^M
>> ../../../repos/binutils-gdb/gdb/frame.c:1441^M
>> 0xaaaaabc55243 aarch64_pseudo_write_1^M
>> ../../../repos/binutils-gdb/gdb/aarch64-tdep.c:3316^M
>> 0xaaaaabc5c943 aarch64_pseudo_write^M
>> ../../../repos/binutils-gdb/gdb/aarch64-tdep.c:3414^M
>
> Ok, then I presume the regression is introduced with patch "gdb: migrate
> aarch64 to new gdbarch_pseudo_register_write".
>
>> It is also worth noting that the v registers are *not* pseudo-registers when the aarch64-fpu feature is used. If SVE
>> is available though, then that means the v registers are pseudo-registers as well. You can tell them apart by their types.
>>
>> Real register (no SVE support):
>>
>> type = union aarch64v {
>> vnd d;
>> vns s;
>> vnh h;
>> vnb b;
>> vnq q;
>> }
>>
>> Pseudo-register (SVE support):
>>
>> union __gdb_builtin_type_vnv {
>> __gdb_builtin_type_vnd d;
>> __gdb_builtin_type_vns s;
>> __gdb_builtin_type_vnh h;
>> __gdb_builtin_type_vnb b;
>> __gdb_builtin_type_vnq q;
>> }
>
> Ok, thanks for that explanation. If you recall, I asked you on IRC if
> the V registers were always 16 bytes long, and you said yes. That's why
> I hardcoded the size of 16 in aarch64_pseudo_write_1. But then

Right. The V registers are always 16 bytes long, being real or pseudo-registers. So
their sizes are fixed.

The other pseudo-registers are also fixed size. What chages is the size of the SVE
register the V/Q/D/S/H/B pseudo-registers map to.

> according to your explanation, when SVE is available, the raw register
> behind S registers, for instance, is an SVE register whose length is
> unknown at compile time. That's why the existing code calls
> register_size to get the size of the raw register.
>
> If you apply the patch below, does it help?

It gets rid of the internal error due to the assertion, but I still see FAIL's due to wrong
values being printed.

FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change: p/x $v8.q.u
FAIL: gdb.arch/aarch64-pseudo-unwind.exp: caller, after change: p/x $v8.q.u
FAIL: gdb.arch/aarch64-pseudo-unwind.exp: caller, after change: p/x $s8.u
FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change in caller: p/x $v8.q.u
FAIL: gdb.arch/aarch64-pseudo-unwind.exp: continue to breakpoint: continue to break_here_c
FAIL: gdb.arch/aarch64-pseudo-unwind.exp: p/x value
FAIL: gdb.arch/aarch64-fp.exp: bfloat16: h0 fields are valid

p/x $v8.q.u
$3 = {0xaaab34353637}
(gdb) FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change: p/x $v8.q.u
--
p/x $v8.q.u
$7 = {0xaaab34353637}
(gdb) FAIL: gdb.arch/aarch64-pseudo-unwind.exp: caller, after change: p/x $v8.q.u
--
p/x $s8.u
$8 = 0x34353637
(gdb) FAIL: gdb.arch/aarch64-pseudo-unwind.exp: caller, after change: p/x $s8.u
--
p/x $v8.q.u
$9 = {0xaaab34353637}
(gdb) FAIL: gdb.arch/aarch64-pseudo-unwind.exp: callee, after change in caller: p/x $v8.q.u
--
Program received signal SIGSEGV, Segmentation fault.
0x0000aaab0fad6e60 in ?? ()
(gdb) FAIL: gdb.arch/aarch64-pseudo-unwind.exp: continue to breakpoint: continue to break_here_c
p/x value
No symbol "value" in current context.
(gdb) FAIL: gdb.arch/aarch64-pseudo-unwind.exp: p/x value
testcase binutils-gdb/gdb/testsuite/gdb.arch/aarch64-pseudo-unwind.exp completed in 1 seconds
Running binutils-gdb/gdb/testsuite/gdb.arch/aarch64-fp.exp ...
--
p $h0
$7 = {bf = 1.136e-28, f = 0.00061798, u = 4368, s = 4368}
(gdb) FAIL: gdb.arch/aarch64-fp.exp: bfloat16: h0 fields are valid

>
> Simon
>
>
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 1815d78dec40..87e6f9e10ae2 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -3300,7 +3300,7 @@ aarch64_pseudo_write_1 (gdbarch *gdbarch, frame_info_ptr next_frame,
> int regnum_offset,
> gdb::array_view<const gdb_byte> buf)
> {
> - unsigned v_regnum = AARCH64_V0_REGNUM + regnum_offset;
> + unsigned raw_regnum = AARCH64_V0_REGNUM + regnum_offset;
> gdb_static_assert (AARCH64_V0_REGNUM == AARCH64_SVE_Z0_REGNUM);
>
> /* Enough space for a full vector register.
> @@ -3309,11 +3309,11 @@ aarch64_pseudo_write_1 (gdbarch *gdbarch, frame_info_ptr next_frame,
> various 'scalar' pseudo registers to behavior like architectural
> writes, register width bytes are written the remainder are set to
> zero. */
> - constexpr int raw_reg_size = 16;
> - gdb_byte raw_buf[raw_reg_size] {};
> + int raw_reg_size = register_size (gdbarch, raw_regnum);
> + gdb::byte_vector raw_buf (raw_reg_size);
> gdb::array_view<gdb_byte> raw_view (raw_buf);
> copy (buf, raw_view.slice (0, buf.size ()));
> - put_frame_register (next_frame, v_regnum, raw_view);
> + put_frame_register (next_frame, raw_regnum, raw_view);
> }
>
> /* Given REGNUM, a SME pseudo-register number, store the bytes from DATA to the
>