Commit Graph

224 Commits

Author SHA1 Message Date
Peter Maydell
e63f70f980 target/arm: Add _aa32_ to isar_feature functions testing 32-bit ID registers
Enforce a convention that an isar_feature function that tests a
32-bit ID register always has _aa32_ in its name, and one that
tests a 64-bit ID register always has _aa64_ in its name.
We already follow this except for three cases: thumb_div,
arm_div and jazelle, which all need _aa32_ adding.

(As noted in the comment, isar_feature_aa32_fp16_arith()
is an exception in that it currently tests ID_AA64PFR0_EL1,
but will switch to MVFR1 once we've properly implemented
FP16 for AArch32.)

Backports commit 873b73c0c891ec20adacc7bd1ae789294334d675 from qemu
2020-03-21 18:08:23 -04:00
Richard Henderson
5b5050c6ca target/arm: Update MSR access to UAO
Backports commit 9eeb7a1c9531cb3574bfe2c36eb7624802c3ec00 from qemu
2020-03-21 17:48:01 -04:00
Richard Henderson
0630e66b5a target/arm: Add ID_AA64MMFR2_EL1
Add definitions for all of the fields, up to ARMv8.5.
Convert the existing RESERVED register to a full register.
Query KVM for the value of the register for the host.

Backports commit 64761e10af2742a916c08271828890274137b9e8 from qemu
2020-03-21 17:45:27 -04:00
Richard Henderson
35fab80c57 target/arm: Update MSR access for PAN
For aarch64, there's a dedicated msr (imm, reg) insn.
For aarch32, this is done via msr to cpsr. Writes from el0
are ignored, which is already handled by the CPSR_USER mask.

Backports commit 220f508f49c5f49fb771d5105f991c19ffede3f7 from qemu
2020-03-21 17:33:16 -04:00
Richard Henderson
b6b69d7ac5 target/arm: Remove CPSR_RESERVED
The only remaining use was in op_helper.c. Use PSTATE_SS
directly, and move the commentary so that it is more obvious
what is going on.

Backports commit 70dae0d069c45250bbefd9424089383a8ac239de from qemu
2020-03-21 17:24:21 -04:00
Richard Henderson
c450694f1a target/arm: Replace CPSR_ERET_MASK with aarch32_cpsr_valid_mask
CPSR_ERET_MASK was a useless renaming of CPSR_RESERVED.
The function also takes into account bits that the cpu
does not support.

Backports commit 437864216d63f052f3cd06ec8861d0e432496424 from qemu
2020-03-21 17:19:17 -04:00
Richard Henderson
5c8c2ca505 target/arm: Add isar_feature tests for PAN + ATS1E1
Include definitions for all of the bits in ID_MMFR3.
We already have a definition for ID_AA64MMFR1.PAN.

Backports commit 3d6ad6bb466f487bcc861f99e2c9054230df1076 from qemu
2020-03-21 17:13:07 -04:00
Richard Henderson
7aaf0d442b target/arm: Add mmu_idx for EL1 and EL2 w/ PAN enabled
To implement PAN, we will want to swap, for short periods
of time, to a different privileged mmu_idx. In addition,
we cannot do this with flushing alone, because the AT*
instructions have both PAN and PAN-less versions.

Add the ARMMMUIdx*_PAN constants where necessary next to
the corresponding ARMMMUIdx* constant.

Backports commit 452ef8cb8c7b06f44a30a3c3a54d3be82c4aef59 from qemu
2020-03-21 17:12:16 -04:00
Richard Henderson
6023db20bc target/arm: Move arm_excp_unmasked to cpu.c
This inline function has one user in cpu.c, and need not be exposed
otherwise. Code movement only, with fixups for checkpatch.

Backports commit 310cedf39dea240a89f90729fd99481ff6158e90 from qemu
2020-03-21 16:37:12 -04:00
Richard Henderson
8f1201e392 target/arm: Update get_a64_user_mem_index for VHE
The EL2&0 translation regime is affected by Load Register (unpriv).

The code structure used here will facilitate later changes in this
area for implementing UAO and NV.

Backports commit cc28fc30e333dc2f20ebfde54444697e26cd8f6d from qemu
2020-03-21 16:33:52 -04:00
Richard Henderson
e41c51f6da target/arm: Add VHE system register redirection and aliasing
Several of the EL1/0 registers are redirected to the EL2 version when in
EL2 and HCR_EL2.E2H is set. Many of these registers have side effects.
Link together the two ARMCPRegInfo structures after they have been
properly instantiated. Install common dispatch routines to all of the
relevant registers.

The same set of registers that are redirected also have additional
EL12/EL02 aliases created to access the original register that was
redirected.

Omit the generic timer registers from redirection here, because we'll
need multiple kinds of redirection from both EL0 and EL2.

Backports commit e2cce18f5c1d0d55328c585c8372cdb096bbf528 from qemu
2020-03-21 15:57:03 -04:00
Richard Henderson
d6150127b4 target/arm: Add the hypervisor virtual counter
Backports commit 8c94b071a09c2183f032febff3112f2b7662156c from qemu
2020-03-21 15:35:36 -04:00
Richard Henderson
3a5135473f target/arm: Update arm_sctlr for VHE
Use the correct sctlr for EL2&0 regime. Due to header ordering,
and where arm_mmu_idx_el is declared, we need to move the function
out of line. Use the function in many more places in order to
select the correct control.

Backports commit aaec143212bb70ac9549cf73203d13100bd5c7c2 from qemu
2020-03-21 15:29:21 -04:00
Richard Henderson
0318d7af99 target/arm: Reorganize ARMMMUIdx
Prepare for, but do not yet implement, the EL2&0 regime.
This involves adding the new MMUIdx enumerators and adjusting
some of the MMUIdx related predicates to match.

Backports commit b9f6033c1a5fb7da55ed353794db8ec064f78bb2 from qemu.
2020-03-21 15:10:05 -04:00
Richard Henderson
85a7cfbdc6 target/arm: Tidy ARMMMUIdx m-profile definitions
Replace the magic numbers with the relevant ARM_MMU_IDX_M_* constants.
Keep the definitions short by referencing previous symbols.

Backports commit 25568316b2a7e73d68701042ba6ebdb217205e20 from qemu
2020-03-21 14:58:17 -04:00
Richard Henderson
c223708063 target/arm: Rearrange ARMMMUIdxBit
Define via macro expansion, so that renumbering of the base ARMMMUIdx
symbols is automatically reflected in the bit definitions.

Backports commit 5f09a6dfbfbff4662f52cc3130a2e07044816497 from qemu
2020-03-21 14:56:46 -04:00
Richard Henderson
56504d255b target/arm: Expand TBFLAG_ANY.MMUIDX to 4 bits
We are about to expand the number of mmuidx to 10, and so need 4 bits.
For the benefit of reading the number out of -d exec, align it to the
penultimate nibble.

Backports commit 506f149815c2168f16ade17893e117419d93f248 from qemu
2020-03-21 14:54:55 -04:00
Richard Henderson
be3c71fb8b target/arm: Recover 4 bits from TBFLAGs
We had completely run out of TBFLAG bits.
Split A- and M-profile bits into two overlapping buckets.
This results in 4 free bits.

We used to initialize all of the a32 and m32 fields in DisasContext
by assignment, in arm_tr_init_disas_context. Now we only initialize
either the a32 or m32 by assignment, because the bits overlap in
tbflags. So zero the entire structure in gen_intermediate_code.

Backports commit 79cabf1f473ca6e9fa0727f64ed9c2a84a36f0aa from qemu
2020-03-21 14:51:46 -04:00
Richard Henderson
153d7aadd5 target/arm: Rename ARMMMUIdx_S1E2 to ARMMMUIdx_E2
This is part of a reorganization to the set of mmu_idx.
The non-secure EL2 regime only has a single stage translation;
there is no point in pointing out that the idx is for stage1.

Backports commit e013b7411339342aac8d986c5d5e329e1baee8e1 from qemu
2020-03-21 14:42:23 -04:00
Richard Henderson
f45ab0614e target/arm: Rename ARMMMUIdx*_S1E3 to ARMMMUIdx*_SE3
This is part of a reorganization to the set of mmu_idx.
The EL3 regime only has a single stage translation, and
is always secure.

Backports commit 127b2b086303296289099a6fb10bbc51077f1d53 from qemu
2020-03-21 14:38:44 -04:00
Richard Henderson
1a672fc3b1 target/arm: Rename ARMMMUIdx_S1SE[01] to ARMMMUIdx_SE10_[01]
This is part of a reorganization to the set of mmu_idx.
This emphasizes that they apply to the Secure EL1&0 regime.

Backports commit fba37aedecb82506c62a1f9e81d066b4fd04e443 from qemu
2020-03-21 14:35:28 -04:00
Richard Henderson
31837384b3 target/arm: Rename ARMMMUIdx_S1NSE* to ARMMMUIdx_Stage1_E*
This is part of a reorganization to the set of mmu_idx.
The EL1&0 regime is the only one that uses 2-stage translation.
Spelling out Stage avoids confusion with Secure.

Backports commit 2859d7b590760283a7b5aef40b723e9dfd7c98ba from qemu
2020-03-21 14:20:31 -04:00
Richard Henderson
b62b4c4f35 target/arm: Rename ARMMMUIdx_S2NS to ARMMMUIdx_Stage2
The EL1&0 regime is the only one that uses 2-stage translation.

Backports commit 97fa9350017e647151dd1dc212f1bbca0294dba7 from qemu
2020-03-21 14:15:35 -04:00
Richard Henderson
ec05f22e82 target/arm: Rename ARMMMUIdx*_S12NSE* to ARMMMUIdx*_E10_*
This is part of a reorganization to the set of mmu_idx.
This emphasizes that they apply to the EL1&0 regime.

The ultimate goal is

-- Non-secure regimes:
ARMMMUIdx_E10_0,
ARMMMUIdx_E20_0,
ARMMMUIdx_E10_1,
ARMMMUIdx_E2,
ARMMMUIdx_E20_2,

-- Secure regimes:
ARMMMUIdx_SE10_0,
ARMMMUIdx_SE10_1,
ARMMMUIdx_SE3,

-- Helper mmu_idx for non-secure EL1&0 stage1 and stage2
ARMMMUIdx_Stage2,
ARMMMUIdx_Stage1_E0,
ARMMMUIdx_Stage1_E1,

The 'S' prefix is reserved for "Secure". Unless otherwise specified,
each mmu_idx represents all stages of translation.

Backports commit 01b98b686460b3a0fb47125882e4f8d4268ac1b6 from qemu
2020-03-21 14:09:15 -04:00
Richard Henderson
fe6825ca4d target/arm: Enable HCR_E2H for VHE
Backports commit 03c76131bc494366a4357a1d265c5eb5cc820754 from qemu
2020-03-21 13:35:00 -04:00
Richard Henderson
5455bd4037 target/arm: Define isar_feature_aa64_vh
Backports commit 8fc2ea21f75923b427eba261eb70f4a258f1b4e5 from qemu
2020-03-21 13:34:11 -04:00
Alex Bennée
639c5c4fe2 target/arm: ensure we use current exception state after SCR update
A write to the SCR can change the effective EL by droppping the system
from secure to non-secure mode. However if we use a cached current_el
from before the change we'll rebuild the flags incorrectly. To fix
this we introduce the ARM_CP_NEWEL CP flag to indicate the new EL
should be used when recomputing the flags.

Backports partof commit f80741d107673f162e3b097fc76a1590036cc9d1 from
qemu
2020-01-14 07:51:10 -05:00
Beata Michalska
81c14bb595 target/arm: Add support for DC CVAP & DC CVADP ins
ARMv8.2 introduced support for Data Cache Clean instructions
to PoP (point-of-persistence) - DC CVAP and PoDP (point-of-deep-persistence)
- DV CVADP. Both specify conceptual points in a memory system where all writes
that are to reach them are considered persistent.
The support provided considers both to be actually the same so there is no
distinction between the two. If none is available (there is no backing store
for given memory) both will result in Data Cache Clean up to the point of
coherency. Otherwise sync for the specified range shall be performed.

Backports commit 0d57b49992200a926c4436eead97ecfc8cc710be from qemu
2020-01-14 07:47:48 -05:00
Marc Zyngier
457934855b target/arm: Handle AArch32 CP15 trapping via HSTR_EL2
HSTR_EL2 offers a way to trap ranges of CP15 system register
accesses to EL2, and it looks like this register is completely
ignored by QEMU.

To avoid adding extra .accessfn filters all over the place (which
would have a direct performance impact), let's add a new TB flag
that gets set whenever HSTR_EL2 is non-zero and that QEMU translates
a context where this trap has a chance to apply, and only generate
the extra access check if the hypervisor is actively using this feature.

Tested with a hand-crafted KVM guest accessing CBAR.

Backports commit 5bb0a20b74ad17dee5dae38e3b8b70b383ee7c2d from qemu
2020-01-07 18:07:21 -05:00
Richard Henderson
f2ec6bc22d
target/arm: Support EL0 v7m msr/mrs for CONFIG_USER_ONLY
Simply moving the non-stub helper_v7m_mrs/msr outside of
!CONFIG_USER_ONLY is not an option, because of all of the
other system-mode helpers that are called.

But we can split out a few subroutines to handle the few
EL0 accessible registers without duplicating code.

Backports commit 04c9c81b8fa2ee33f59a26265700fae6fc646062 from qemu
2019-11-28 03:29:46 -05:00
Peter Maydell
56b54f361e
target/arm: Allow ARMCPRegInfo read/write functions to throw exceptions
Currently the only part of an ARMCPRegInfo which is allowed to cause
a CPU exception is the access function, which returns a value indicating
that some flavour of UNDEF should be generated.

For the ATS system instructions, we would like to conditionally
generate exceptions as part of the writefn, because some faults
during the page table walk (like external aborts) should cause
an exception to be raised rather than returning a value.

There are several ways we could do this:
* plumb the GETPC() value from the top level set_cp_reg/get_cp_reg
helper functions through into the readfn and writefn hooks
* add extra readfn_with_ra/writefn_with_ra hooks that take the GETPC()
value
* require the ATS instructions to provide a dummy accessfn,
which serves no purpose except to cause the code generation
to emit TCG ops to sync the CPU state
* add an ARM_CP_ flag to mark the ARMCPRegInfo as possibly
throwing an exception in its read/write hooks, and make the
codegen sync the CPU state before calling the hooks if the
flag is set

This patch opts for the last of these, as it is fairly simple
to implement and doesn't require invasive changes like updating
the readfn/writefn hook function prototype signature.

Backports commit 37ff584c15bc3e1dd2c26b1998f00ff87189538c from qemu
2019-11-20 17:24:37 -05:00
Andrew Jones
ad63ee7509
target/arm/cpu: Use div-round-up to determine predicate register array size
Unless we're guaranteed to always increase ARM_MAX_VQ by a multiple of
four, then we should use DIV_ROUND_UP to ensure we get an appropriate
array size.

Backports commit 46417784d21c89446763f2047228977bdc267895 from qemu
2019-11-18 20:16:46 -05:00
Peter Maydell
c61e22627d
target/arm: Fix routing of singlestep exceptions
When generating an architectural single-step exception we were
routing it to the "default exception level", which is to say
the same exception level we execute at except that EL0 exceptions
go to EL1. This is incorrect because the debug exception level
can be configured by the guest for situations such as single
stepping of EL0 and EL1 code by EL2.

We have to track the target debug exception level in the TB
flags, because it is dependent on CPU state like HCR_EL2.TGE
and MDCR_EL2.TDE. (That we were previously calling the
arm_debug_target_el() function to determine dc->ss_same_el
is itself a bug, though one that would only have manifested
as incorrect syndrome information.) Since we are out of TB
flag bits unless we want to expand into the cs_base field,
we share some bits with the M-profile only HANDLER and
STACKCHECK bits, since only A-profile has this singlestep.

Fixes: https://bugs.launchpad.net/qemu/+bug/1838913

Backports commit 8bd587c1066f4456ddfe611b571d9439a947d74c from qemu
2019-11-18 16:50:15 -05:00
Alex Bennée
0d6ed39333
target/arm: generate a custom MIDR for -cpu max
While most features are now detected by probing the ID_* registers
kernels can (and do) use MIDR_EL1 for working out of they have to
apply errata. This can trip up warnings in the kernel as it tries to
work out if it should apply workarounds to features that don't
actually exist in the reported CPU type.

Avoid this problem by synthesising our own MIDR value.

Backports commit 2bd5f41c00686a1f847a60824d0375f3df2c26bf from qemu
2019-11-18 16:42:51 -05:00
Philippe Mathieu-Daudé
199e2f8a7d
target/arm: Restrict semi-hosting to TCG
Semihosting hooks either SVC or HLT instructions, and inside KVM
both of those go to EL1, ie to the guest, and can't be trapped to
KVM.

Let check_for_semihosting() return False when not running on TCG.

backports commit 91f78c58da9ba78c8ed00f5d822b701765be8499 from qemu
2019-08-08 17:48:34 -04:00
Peter Maydell
dc1f2247ec
target/arm: Only implement doubles if the FPU supports them
The architecture permits FPUs which have only single-precision
support, not double-precision; Cortex-M4 and Cortex-M33 are
both like that. Add the necessary checks on the MVFR0 FPDP
field so that we UNDEF any double-precision instructions on
CPUs like this.

Note that even if FPDP==0 the insns like VMOV-to/from-gpreg,
VLDM/VSTM, VLDR/VSTR which take double precision registers
still exist.

Backports commit 1120827fa182f0e76226df7ffe7a86598d1df54f from qemu
2019-06-25 18:55:25 -05:00
Peter Maydell
edf81eb214
target/arm: Convert VFP VMLA to decodetree
Convert the VFP VMLA instruction to decodetree.

This is the first of the VFP 3-operand data processing instructions,
so we include in this patch the code which loops over the elements
for an old-style VFP vector operation. The existing code to do this
looping uses the deprecated cpu_F0s/F0d/F1s/F1d TCG globals; since
we are going to be converting instructions one at a time anyway
we can take the opportunity to make the new loop use TCG temporaries,
which means we can do that conversion one operation at a time
rather than needing to do it all in one go.

We include an UNDEF check which was missing in the old code:
short-vector operations (with stride or length non-zero) were
deprecated in v7A and must UNDEF in v8A, so if the MVFR0 FPShVec
field does not indicate that support for short vectors is present
we UNDEF the operations that would use them. (This is a change
of behaviour for Cortex-A7, Cortex-A15 and the v8 CPUs, which
previously were all incorrectly allowing short-vector operations.)

Note that the conversion fixes a bug in the old code for the
case of VFP short-vector "mixed scalar/vector operations". These
happen where the destination register is in a vector bank but
but the second operand is in a scalar bank. For example
vmla.f64 d10, d1, d16 with length 2 stride 2
is equivalent to the pair of scalar operations
vmla.f64 d10, d1, d16
vmla.f64 d8, d3, d16
where the destination and first input register cycle through
their vector but the second input is scalar (d16). In the
old decoder the gen_vfp_F1_mul() operation uses cpu_F1{s,d}
as a temporary output for the multiply, which trashes the
second input operand. For the fully-scalar case (where we
never do a second iteration) and the fully-vector case
(where the loop loads the new second input operand) this
doesn't matter, but for the mixed scalar/vector case we
will end up using the wrong value for later loop iterations.
In the new code we use TCG temporaries and so avoid the bug.
This bug is present for all the multiply-accumulate insns
that operate on short vectors: VMLA, VMLS, VNMLA, VNMLS.

Note 2: the expression used to calculate the next register
number in the vector bank is not in fact correct; we leave
this behaviour unchanged from the old decoder and will
fix this bug later in the series.

Backports commit 266bd25c485597c94209bfdb3891c1d0c573c164 from qemu
2019-06-13 17:59:16 -04:00
Peter Maydell
3994dfd079
target/arm: Convert the VSEL instructions to decodetree
Convert the VSEL instructions to decodetree.
We leave trans_VSEL() in translate.c for now as this allows
the patch to show just the changes from the old handle_vsel().

In the old code the check for "do D16-D31 exist" was hidden in
the VFP_DREG macro, and assumed that VFPv3 always implied that
D16-D31 exist. In the new code we do the correct ID register test.
This gives identical behaviour for most of our CPUs, and fixes
previously incorrect handling for Cortex-R5F, Cortex-M4 and
Cortex-M33, which all implement VFPv3 or better with only 16
double-precision registers.

Backports commit b3ff4b87b4ae08120a51fe12592725e1dca8a085 from qemu
2019-06-13 16:41:22 -04:00
Richard Henderson
8f53f09a05
cpu: Introduce CPUNegativeOffsetState
Nothing in there so far, but all of the plumbing done
within the target ArchCPU state.

Backports commit 5b146dc716cfd247f99556c04e6e46fbd67565a0 from qemu
2019-06-13 15:08:25 -04:00
Richard Henderson
ac176ccb38
cpu: Move ENV_OFFSET to exec/gen-icount.h
Now that we have ArchCPU, we can define this generically,
in the one place that needs it.

Backports commit 677c4d69ac21961e76a386f9bfc892a44923acc0 from qemu
2019-06-12 12:20:21 -04:00
Richard Henderson
b8bd543390
target/arm: Use env_cpu, env_archcpu
Cleanup in the boilerplate that each target must define.
Replace arm_env_get_cpu with env_archcpu. The combination
CPU(arm_env_get_cpu) should have used ENV_GET_CPU to begin;
use env_cpu now.

Backports commit 2fc0cc0e1e034582f4718b1a2d57691474ccb6aa from qemu
2019-06-12 11:34:08 -04:00
Richard Henderson
fbf91a6535
cpu: Replace ENV_GET_CPU with env_cpu
Now that we have both ArchCPU and CPUArchState, we can define
this generically instead of via macro in each target's cpu.h.

Backports commit 29a0af618ddd21f55df5753c3e16b0625f534b3c from qemu
2019-06-12 11:16:16 -04:00
Richard Henderson
ae94fb5992
cpu: Define ArchCPU
For all targets, do this just before including exec/cpu-all.h.

Backports commit 2161a612b4e1d388046320bc464adefd6bba01a0 from qemu
2019-06-12 11:08:39 -04:00
Richard Henderson
e3f1f25996
cpu: Define CPUArchState with typedef
For all targets, do this just before including exec/cpu-all.h.

Backports commit 4f7c64b3819d559417615ed2b1d028ebc1a49580 from qemu
2019-06-12 11:06:36 -04:00
Richard Henderson
df2a890bd7
tcg: Split out target/arch/cpu-param.h
For all targets, into this new file move TARGET_LONG_BITS,
TARGET_PAGE_BITS, TARGET_PHYS_ADDR_SPACE_BITS,
TARGET_VIRT_ADDR_SPACE_BITS, and NB_MMU_MODES.

Include this new file from exec/cpu-defs.h.

This now removes the somewhat odd requirement that target/arch/cpu.h
defines TARGET_LONG_BITS before including exec/cpu-defs.h, so push the
bulk of the includes within target/arch/cpu.h to the top.

Backports commit 74433bf083b0766aba81534f92de13194f23ff3e from qemu
2019-06-10 19:35:46 -04:00
Richard Henderson
3dd7358a53
target/arm: Implement ARMv8.5-RNG
Use the newly introduced infrastructure for guest random numbers.

Backports commit de390645675966cce113bf5394445bc1f8d07c85 from qemu

(with the actual RNG portion disabled to preserve determinism for the
time being).
2019-05-23 15:03:23 -04:00
Richard Henderson
a8df33c37c
target/arm: Put all PAC keys into a structure
This allows us to use a single syscall to initialize them all.

Backports commit 108b3ba891408c4dce93df78261ec4aca38c0e2e from qemu
2019-05-23 14:54:06 -04:00
Peter Maydell
7861820e94
target/arm: Implement XPSR GE bits
In the M-profile architecture, if the CPU implements the DSP extension
then the XPSR has GE bits, in the same way as the A-profile CPSR. When
we added DSP extension support we forgot to add support for reading
and writing the GE bits, which are stored in env->GE. We did put in
the code to add XPSR_GE to the mask of bits to update in the v7m_msr
helper, but forgot it in v7m_mrs. We also must not allow the XPSR we
pull off the stack on exception return to set the nonexistent GE bits.
Correct these errors:
* read and write env->GE in xpsr_read() and xpsr_write()
* only set GE bits on exception return if DSP present
* read GE bits for MRS if DSP present

Backports commit f1e2598c46d480c9e21213a244bc514200762828 from qemu
2019-05-09 17:46:31 -04:00
Peter Maydell
b483951046
target/arm: Implement VLSTM for v7M CPUs with an FPU
Implement the VLSTM instruction for v7M for the FPU present case.

Backports commit 019076b036da4444494de38388218040d9d3a26c from qemu
2019-04-30 11:25:44 -04:00
Peter Maydell
a976d7642a
target/arm: Implement M-profile lazy FP state preservation
The M-profile architecture floating point system supports
lazy FP state preservation, where FP registers are not
pushed to the stack when an exception occurs but are instead
only saved if and when the first FP instruction in the exception
handler is executed. Implement this in QEMU, corresponding
to the check of LSPACT in the pseudocode ExecuteFPCheck().

Backports commit e33cf0f8d8c9998a7616684f9d6aa0d181b88803 from qemu
2019-04-30 11:21:50 -04:00