target/arm: Prepare DBGBVR and DBGWVR for FEAT_LVA

The original A.a revision of the AArch64 ARM required that we
force-extend the addresses in these registers from 49 bits.
This language has been loosened via a combination of IMPLEMENTATION
DEFINED and CONSTRAINTED UNPREDICTABLE to allow consideration of
the entire aligned address.

This means that we do not have to consider whether or not FEAT_LVA
is enabled, and decide from which bit an address might need to be
extended.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220301215958.157011-9-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 24 insertions, 8 deletions

diff --git a/target/arm/helper.c b/target/arm/helper.c
index c002100..2eff30d 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -6423,11 +6423,18 @@ static void dbgwvr_write(CPUARMState *env, const ARMCPRegInfo *ri,
     ARMCPU *cpu = env_archcpu(env);
     int i = ri->crm;
 
-    /* Bits [63:49] are hardwired to the value of bit [48]; that is, the
-     * register reads and behaves as if values written are sign extended.
+    /*
      * Bits [1:0] are RES0.
+     *
+     * It is IMPLEMENTATION DEFINED whether [63:49] ([63:53] with FEAT_LVA)
+     * are hardwired to the value of bit [48] ([52] with FEAT_LVA), or if
+     * they contain the value written.  It is CONSTRAINED UNPREDICTABLE
+     * whether the RESS bits are ignored when comparing an address.
+     *
+     * Therefore we are allowed to compare the entire register, which lets
+     * us avoid considering whether or not FEAT_LVA is actually enabled.
      */
-    value = sextract64(value, 0, 49) & ~3ULL;
+    value &= ~3ULL;
 
     raw_write(env, ri, value);
     hw_watchpoint_update(cpu, i);
@@ -6473,10 +6480,19 @@ void hw_breakpoint_update(ARMCPU *cpu, int n)
     case 0: /* unlinked address match */
     case 1: /* linked address match */
     {
-        /* Bits [63:49] are hardwired to the value of bit [48]; that is,
-         * we behave as if the register was sign extended. Bits [1:0] are
-         * RES0. The BAS field is used to allow setting breakpoints on 16
-         * bit wide instructions; it is CONSTRAINED UNPREDICTABLE whether
+        /*
+         * Bits [1:0] are RES0.
+         *
+         * It is IMPLEMENTATION DEFINED whether bits [63:49]
+         * ([63:53] for FEAT_LVA) are hardwired to a copy of the sign bit
+         * of the VA field ([48] or [52] for FEAT_LVA), or whether the
+         * value is read as written.  It is CONSTRAINED UNPREDICTABLE
+         * whether the RESS bits are ignored when comparing an address.
+         * Therefore we are allowed to compare the entire register, which
+         * lets us avoid considering whether FEAT_LVA is actually enabled.
+         *
+         * The BAS field is used to allow setting breakpoints on 16-bit
+         * wide instructions; it is CONSTRAINED UNPREDICTABLE whether
          * a bp will fire if the addresses covered by the bp and the addresses
          * covered by the insn overlap but the insn doesn't start at the
          * start of the bp address range. We choose to require the insn and
@@ -6489,7 +6505,7 @@ void hw_breakpoint_update(ARMCPU *cpu, int n)
          * See also figure D2-3 in the v8 ARM ARM (DDI0487A.c).
          */
         int bas = extract64(bcr, 5, 4);
-        addr = sextract64(bvr, 0, 49) & ~3ULL;
+        addr = bvr & ~3ULL;
         if (bas == 0) {
             return;
         }