target/ppc: Ease L=0 requirement on cmp/cmpi/cmpl/cmpli for ppc32

In commit 8f0a4b6a9b, we started to require L=0 for ppc32 to match what
The Programming Environments Manual say:

"For 32-bit implementations, the L field must be cleared, otherwise
the instruction form is invalid."

The stricter behavior, however, broke AROS boot on sam460ex, which is a
regression from 6.0. This patch partially reverts the change, raising
the exception only for CPUs known to require L=0 (e500 and e500mc) and
logging a guest error for other cases.

Both behaviors are acceptable by the PowerISA, which allows "the system
illegal instruction error handler to be invoked or yield boundedly
undefined results."

Reported-by: BALATON Zoltan <balaton@eik.bme.hu>
Fixes: 8f0a4b6a9b ("target/ppc: Move cmp/cmpi/cmpl/cmpli to decodetree")
Tested-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20210720135507.2444635-1-matheus.ferst@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 56 insertions, 2 deletions

diff --git a/target/ppc/translate/fixedpoint-impl.c.inc b/target/ppc/translate/fixedpoint-impl.c.inc
index 8864ac4..2e2518e 100644
--- a/target/ppc/translate/fixedpoint-impl.c.inc
+++ b/target/ppc/translate/fixedpoint-impl.c.inc
@@ -171,8 +171,35 @@ TRANS64(PSTD, do_ldst_PLS_D, false, true, MO_Q)
 
 static bool do_cmp_X(DisasContext *ctx, arg_X_bfl *a, bool s)
 {
+    if ((ctx->insns_flags & PPC_64B) == 0) {
+        /*
+         * For 32-bit implementations, The Programming Environments Manual says
+         * that "the L field must be cleared, otherwise the instruction form is
+         * invalid." It seems, however, that most 32-bit CPUs ignore invalid
+         * forms (e.g., section "Instruction Formats" of the 405 and 440
+         * manuals, "Integer Compare Instructions" of the 601 manual), with the
+         * notable exception of the e500 and e500mc, where L=1 was reported to
+         * cause an exception.
+         */
+        if (a->l) {
+            if ((ctx->insns_flags2 & PPC2_BOOKE206)) {
+                /*
+                 * For 32-bit Book E v2.06 implementations (i.e. e500/e500mc),
+                 * generate an illegal instruction exception.
+                 */
+                return false;
+            } else {
+                qemu_log_mask(LOG_GUEST_ERROR,
+                        "Invalid form of CMP%s at 0x" TARGET_FMT_lx ", L = 1\n",
+                        s ? "" : "L", ctx->cia);
+            }
+        }
+        gen_op_cmp32(cpu_gpr[a->ra], cpu_gpr[a->rb], s, a->bf);
+        return true;
+    }
+
+    /* For 64-bit implementations, deal with bit L accordingly. */
     if (a->l) {
-        REQUIRE_64BIT(ctx);
         gen_op_cmp(cpu_gpr[a->ra], cpu_gpr[a->rb], s, a->bf);
     } else {
         gen_op_cmp32(cpu_gpr[a->ra], cpu_gpr[a->rb], s, a->bf);
@@ -182,8 +209,35 @@ static bool do_cmp_X(DisasContext *ctx, arg_X_bfl *a, bool s)
 
 static bool do_cmp_D(DisasContext *ctx, arg_D_bf *a, bool s)
 {
+    if ((ctx->insns_flags & PPC_64B) == 0) {
+        /*
+         * For 32-bit implementations, The Programming Environments Manual says
+         * that "the L field must be cleared, otherwise the instruction form is
+         * invalid." It seems, however, that most 32-bit CPUs ignore invalid
+         * forms (e.g., section "Instruction Formats" of the 405 and 440
+         * manuals, "Integer Compare Instructions" of the 601 manual), with the
+         * notable exception of the e500 and e500mc, where L=1 was reported to
+         * cause an exception.
+         */
+        if (a->l) {
+            if ((ctx->insns_flags2 & PPC2_BOOKE206)) {
+                /*
+                 * For 32-bit Book E v2.06 implementations (i.e. e500/e500mc),
+                 * generate an illegal instruction exception.
+                 */
+                return false;
+            } else {
+                qemu_log_mask(LOG_GUEST_ERROR,
+                        "Invalid form of CMP%s at 0x" TARGET_FMT_lx ", L = 1\n",
+                        s ? "I" : "LI", ctx->cia);
+            }
+        }
+        gen_op_cmp32(cpu_gpr[a->ra], tcg_constant_tl(a->imm), s, a->bf);
+        return true;
+    }
+
+    /* For 64-bit implementations, deal with bit L accordingly. */
     if (a->l) {
-        REQUIRE_64BIT(ctx);
         gen_op_cmp(cpu_gpr[a->ra], tcg_constant_tl(a->imm), s, a->bf);
     } else {
         gen_op_cmp32(cpu_gpr[a->ra], tcg_constant_tl(a->imm), s, a->bf);