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arch-arm: Add UNSERIALIZE flag to address cpt compatibility

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This patch is adding the MISCREG_UNSERIALIZE flag to expose
the user to the following checkpoint compatibility problem:

What happens when a checkpoint is restored with a different
architectural configuration?

The current behaviour is to silently restore the checkpoint
and to populate the ISA registers accordingly. However some of
these restored values will be used and some of them will
be actually discarded.

For example the value of the MISCREG_ID_AA64ISAR0_EL1 register
(initially configured at construction time [1]) will be overwritten by
the checkpointed value in ISA::unserialize (checkpointed params win over
current params). On the other hand we "discard" the checkpointed value
for registers handled in the ISA::readMiscReg method (not accessing the
storage) like MISCREG_ID_AA64PFR0_EL1 [2] (current params win over
checkpointed params).

In other words some registers will be unserialized while some others
will discard the checkpointed value in favour of the current
configuration setup. This categorization is currently implicit and it
ultimately depends on whether or not a register read access its storage
(see MISCREG_ID_AA64PFR0_EL1 above).

With this patch we formalize this distinction. We allow the developer to
be explict on which register should not be unserialized and should
instead use the new simulation parameters.

If there is a mismatch between the reset value of such register and
the checkpointed one, we warn the user and we undo the unserialization
for such register.

[1]: https://github.com/gem5/gem5/blob/v22.1.0.0/src/arch/arm/isa.cc#L437
[2]: https://github.com/gem5/gem5/blob/v22.1.0.0/src/arch/arm/isa.cc#L1019

Change-Id: Icea6563ee5816b14a097926b5734f2fce10530c7
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/70557
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
This commit is contained in:
Giacomo Travaglini
2023-05-10 15:51:12 +01:00
parent 5c60160f3e
commit 9ef7be902b
2 changed files with 20 additions and 1 deletions
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12
src/arch/arm/isa.cc
View File

@@ -1879,6 +1879,18 @@ ISA::unserialize(CheckpointIn &cp)
{
DPRINTF(Checkpoint, "Unserializing Arm Misc Registers\n");
UNSERIALIZE_MAPPING(miscRegs, miscRegName, NUM_PHYS_MISCREGS);
for (auto idx = 0; idx < NUM_MISCREGS; idx++) {
if (!lookUpMiscReg[idx].info[MISCREG_UNSERIALIZE] &&
miscRegs[idx] != lookUpMiscReg[idx].reset()) {
warn("Checkpoint value for register %s does not match "
"current configuration (checkpointed: %#x, current: %#x)",
miscRegName[idx], miscRegs[idx],
lookUpMiscReg[idx].reset());
miscRegs[idx] = lookUpMiscReg[idx].reset();
}
}
CPSR tmp_cpsr = miscRegs[MISCREG_CPSR];
updateRegMap(tmp_cpsr);
}

9
src/arch/arm/regs/misc.hh
View File

@@ -1125,6 +1125,7 @@ namespace ArmISA
MISCREG_IMPLEMENTED,
MISCREG_UNVERIFIABLE, // Does the value change on every read (e.g. a
// arch generic counter)
MISCREG_UNSERIALIZE, // Should the checkpointed value be restored?
MISCREG_WARN_NOT_FAIL, // If MISCREG_IMPLEMENTED is deasserted, it
// tells whether the instruction should raise a
// warning or fail
@@ -1277,6 +1278,12 @@ namespace ArmISA
return *this;
}
chain
unserialize(bool v = true) const
{
entry.info[MISCREG_UNSERIALIZE] = v;
return *this;
}
chain
warnNotFail(bool v = true) const
{
entry.info[MISCREG_WARN_NOT_FAIL] = v;
@@ -1595,7 +1602,7 @@ namespace ArmISA
: entry(e)
{
// force unimplemented registers to be thusly declared
implemented(1);
implemented(1).unserialize(1);
}
};