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target/arm: Don't NOCP fault for FPCXT_NS accesses

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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 9a486856e9, 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
This commit is contained in:
Peter Maydell 2021-06-18 15:10:15 +01:00
parent 9931d9d84b
commit fa856736b6
5 changed files with 542 additions and 528 deletions
Download patch file Download diff file Expand all files Collapse all files

24
target/arm/m-nocp.decode
View file

@ -34,6 +34,14 @@
&nocp cp
# M-profile VLDR/VSTR to sysreg
%vldr_sysreg 22:1 13:3
%imm7_0x4 0:7 !function=times_4
&vldr_sysreg rn reg imm a w p
@vldr_sysreg .... ... . a:1 . . . rn:4 ... . ... .. ....... \
reg=%vldr_sysreg imm=%imm7_0x4 &vldr_sysreg
{
# Special cases which do not take an early NOCP: VLLDM and VLSTM
VLLDM_VLSTM 1110 1100 001 l:1 rn:4 0000 1010 op:1 000 0000
@ -41,6 +49,22 @@
VSCCLRM 1110 1100 1.01 1111 .... 1011 imm:7 0 vd=%vd_dp size=3
VSCCLRM 1110 1100 1.01 1111 .... 1010 imm:8 vd=%vd_sp size=2
# FP system register accesses: these are a special case because accesses
# to FPCXT_NS succeed even if the FPU is disabled. We therefore need
# to handle them before the big NOCP blocks. Note that within these
# insns NOCP still has higher priority than UNDEFs; this is implemented
# by their returning 'false' for UNDEF so as to fall through into the
# NOCP check (in contrast to VLLDM etc, which call unallocated_encoding()
# for the UNDEFs there that must take precedence over NOCP.)
VMSR_VMRS ---- 1110 111 l:1 reg:4 rt:4 1010 0001 0000
# P=0 W=0 is SEE "Related encodings", so split into two patterns
VLDR_sysreg ---- 110 1 . . w:1 1 .... ... 0 111 11 ....... @vldr_sysreg p=1
VLDR_sysreg ---- 110 0 . . 1 1 .... ... 0 111 11 ....... @vldr_sysreg p=0 w=1
VSTR_sysreg ---- 110 1 . . w:1 0 .... ... 0 111 11 ....... @vldr_sysreg p=1
VSTR_sysreg ---- 110 0 . . 1 0 .... ... 0 111 11 ....... @vldr_sysreg p=0 w=1
NOCP 111- 1110 ---- ---- ---- cp:4 ---- ---- &nocp
NOCP 111- 110- ---- ---- ---- cp:4 ---- ---- &nocp
# From v8.1M onwards this range will also NOCP: