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Our current codegen for MVE always calls out to helper functions,
because some byte lanes might be predicated. The common case is that
in fact there is no predication active and all lanes should be
updated together, so we can produce better code by detecting that and
using the TCG generic vector infrastructure.
Add a TB flag that is set when we can guarantee that there is no
active MVE predication, and a bool in the DisasContext. Subsequent
patches will use this flag to generate improved code for some
instructions.
In most cases when the predication state changes we simply end the TB
after that instruction. For the code called from vfp_access_check()
that handles lazy state preservation and creating a new FP context,
we can usually avoid having to try to end the TB because luckily the
new value of the flag following the register changes in those
sequences doesn't depend on any runtime decisions. We do have to end
the TB if the guest has enabled lazy FP state preservation but not
automatic state preservation, but this is an odd corner case that is
not going to be common in real-world code.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210913095440.13462-4-peter.maydell@linaro.org
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Instead of open-coding the "take NOCP exception if FPU disabled,
otherwise call gen_preserve_fp_state()" code in the accessors for
FPCXT_NS, add an argument to vfp_access_check_m() which tells it to
skip the gen_update_fp_context() call, so we can use it for the
FPCXT_NS case.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210618141019.10671-8-peter.maydell@linaro.org
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A few subcases of VLDR/VSTR sysreg succeed but do not perform a
memory access:
* VSTR of VPR when unprivileged
* VLDR to VPR when unprivileged
* VLDR to FPCXT_NS when fpInactive
In these cases, even though we don't do the memory access we should
still update the base register and perform the stack limit check if
the insn's addressing mode specifies writeback. Our implementation
failed to do this, because we handle these side-effects inside the
memory_to_fp_sysreg() and fp_sysreg_to_memory() callback functions,
which are only called if there's something to load or store.
Fix this by adding an extra argument to the callbacks which is set to
true to actually perform the access and false to only do side effects
like writeback, and calling the callback with do_access = false
for the three cases listed above.
This produces slightly suboptimal code for the case of a write
to FPCXT_NS when the FPU is inactive and the insn didn't have
side effects (ie no writeback, or via VMSR), in which case we'll
generate a conditional branch over an unconditional branch.
But this doesn't seem to be important enough to merit requiring
the callback to report back whether it generated any code or not.
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210618141019.10671-5-peter.maydell@linaro.org
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The M-profile architecture requires that accesses to FPCXT_NS when
there is no active FP state must not take a NOCP fault even if the
FPU is disabled. We were not implementing this correctly, because
in our decode we catch the NOCP faults early in m-nocp.decode.
Fix this bug by moving all the handling of M-profile FP system
register accesses from vfp.decode into m-nocp.decode and putting
it above the NOCP blocks. This provides the correct behaviour:
* for accesses other than FPCXT_NS the trans functions call
vfp_access_check(), which will check for FPU disabled and
raise a NOCP exception if necessary
* for FPCXT_NS we have the special case code that doesn't
call vfp_access_check()
* when these trans functions want to raise an UNDEF they return
false, so the decoder will fall through into the NOCP blocks.
This means that NOCP correctly takes precedence over UNDEF
for these insns. (This is a difference from the other insns
handled by m-nocp.decode, where UNDEF takes precedence and
which we implement by having those trans functions call
unallocated_encoding() in the appropriate places.)
[Note for backport to stable: this commit has a semantic dependency
on commit 9a486856e9173af, which was not marked as cc-stable because
we didn't know we'd need it for a for-stable bugfix.]
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210618141019.10671-4-peter.maydell@linaro.org
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On A-profile, PSR bits [15:10][26:25] are always the IT state bits.
On M-profile, some of the reserved encodings of the IT state are used
to instead indicate partial progress through instructions that were
interrupted partway through by an exception and can be resumed.
These resumable instructions fall into two categories:
(1) load/store multiple instructions, where these bits are called
"ICI" and specify the register in the ldm/stm list where execution
should resume. (Specifically: LDM, STM, VLDM, VSTM, VLLDM, VLSTM,
CLRM, VSCCLRM.)
(2) MVE instructions subject to beatwise execution, where these bits
are called "ECI" and specify which beats in this and possibly also
the following MVE insn have been executed.
There are also a few insns (LE, LETP, and BKPT) which do not use the
ICI/ECI bits but must leave them alone.
Otherwise, we should raise an INVSTATE UsageFault for any attempt to
execute an insn with non-zero ICI/ECI bits.
So far we have been able to ignore ECI/ICI, because the architecture
allows the IMPDEF choice of "always restart load/store multiple from
the beginning regardless of ICI state", so the only thing we have
been missing is that we don't raise the INVSTATE fault for bad guest
code. However, MVE requires that we honour ECI bits and do not
rexecute beats of an insn that have already been executed.
Add the support in the decoder for handling ECI/ICI:
* identify the ECI/ICI case in the CONDEXEC TB flags
* when a load/store multiple insn succeeds, it updates the ECI/ICI
state (both in DisasContext and in the CPU state), and sets a flag
to say that the ECI/ICI state was handled
* if we find that the insn we just decoded did not handle the
ECI/ICI state, we delete all the code that we just generated for
it and instead emit the code to raise the INVFAULT. This allows
us to avoid having to update every non-MVE non-LDM/STM insn to
make it check for "is ECI/ICI set?".
We continue with our existing IMPDEF choice of not caring about the
ICI state for the load/store multiples and simply restarting them
from the beginning. Because we don't allow interrupts in the middle
of an insn, the only way we would see this state is if the guest set
ICI manually on return from an exception handler, so it's a corner
case which doesn't merit optimisation.
ICI update for LDM/STM is simple -- it always zeroes the state. ECI
update for MVE beatwise insns will be a little more complex, since
the ECI state may include information for the following insn.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210614151007.4545-5-peter.maydell@linaro.org
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When MVE is supported, the VPR register has a place on the exception
stack frame in a previously reserved slot just above the FPSCR.
It must also be zeroed in various situations when we invalidate
FPU context.
Update the code which handles the stack frames (exception entry and
exit code, VLLDM, and VLSTM) to save/restore VPR.
Update code which invalidates FP registers (mostly also exception
entry and exit code, but also VSCCLRM and the code in
full_vfp_access_check() that corresponds to the ExecuteFPCheck()
pseudocode) to zero VPR.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210614151007.4545-4-peter.maydell@linaro.org
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Currently the trans functions for m-nocp.decode all live in
translate-vfp.inc.c; move them out into their own translation unit,
translate-m-nocp.c.
The trans_* functions here are pure code motion with no changes.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210430132740.10391-5-peter.maydell@linaro.org
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