aboutsummaryrefslogtreecommitdiff
path: root/target/arm/m-nocp.decode
AgeCommit message (Collapse)Author
2021-06-21target/arm: Don't NOCP fault for FPCXT_NS accessesPeter Maydell
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
2020-12-10target/arm: Implement new v8.1M VLLDM and VLSTM encodingsPeter Maydell
v8.1M adds new encodings of VLLDM and VLSTM (where bit 7 is set). The only difference is that: * the old T1 encodings UNDEF if the implementation implements 32 Dregs (this is currently architecturally impossible for M-profile) * the new T2 encodings have the implementation-defined option to read from memory (discarding the data) or write UNKNOWN values to memory for the stack slots that would be D16-D31 We choose not to make those accesses, so for us the two instructions behave identically assuming they don't UNDEF. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20201119215617.29887-21-peter.maydell@linaro.org
2020-12-10target/arm: Implement VSCCLRM insnPeter Maydell
Implement the v8.1M VSCCLRM insn, which zeros floating point registers if there is an active floating point context. This requires support in write_neon_element32() for the MO_32 element size, so add it. Because we want to use arm_gen_condlabel(), we need to move the definition of that function up in translate.c so it is before the #include of translate-vfp.c.inc. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20201119215617.29887-5-peter.maydell@linaro.org
2020-10-20target/arm: Implement v8.1M NOCP handlingPeter Maydell
From v8.1M, disabled-coprocessor handling changes slightly: * coprocessors 8, 9, 14 and 15 are also governed by the cp10 enable bit, like cp11 * an extra range of instruction patterns is considered to be inside the coprocessor space We previously marked these up with TODO comments; implement the correct behaviour. Unfortunately there is no ID register field which indicates this behaviour. We could in theory test an unrelated ID register which indicates guaranteed-to-be-in-v8.1M behaviour like ID_ISAR0.CmpBranch >= 3 (low-overhead-loops), but it seems better to simply define a new ARM_FEATURE_V8_1M feature flag and use it for this and other new-in-v8.1M behaviour that isn't identifiable from the ID registers. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20201019151301.2046-3-peter.maydell@linaro.org
2020-08-24target/arm: Do M-profile NOCP checks early and via decodetreePeter Maydell
For M-profile CPUs, the architecture specifies that the NOCP exception when a coprocessor is not present or disabled should cover the entire wide range of coprocessor-space encodings, and should take precedence over UNDEF exceptions. (This is the opposite of A-profile, where checking for a disabled FPU has to happen last.) Implement this with decodetree patterns that cover the specified ranges of the encoding space. There are a few instructions (VLLDM, VLSTM, and in v8.1 also VSCCLRM) which are in copro-space but must not be NOCP'd: these must be handled also in the new m-nocp.decode so they take precedence. This is a minor behaviour change: for unallocated insn patterns in the VFP area (cp=10,11) we will now NOCP rather than UNDEF when the FPU is disabled. As well as giving us the correct architectural behaviour for v8.1M and the recommended behaviour for v8.0M, this refactoring also removes the old NOCP handling from the remains of the 'legacy decoder' in disas_thumb2_insn(), paving the way for cleaning that up. Since we don't currently have a v8.1M feature bit or any v8.1M CPUs, the minor changes to this logic that we'll need for v8.1M are marked up with TODO comments. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20200803111849.13368-6-peter.maydell@linaro.org