[PATCH 1/2] target/sparc: Loosen decode of STBAR for v8

[Richard Henderson <richard.henderson@linaro.org>]

Solaris 8 appears to have a bug whereby it executes v9 MEMBAR
instructions when booting a freshly installed image. According
to the SPARC v8 architecture manual, whilst bits 13 and bits 12-0
of the "Read State Register Instructions" are notionally zero,
they are marked as unused (i.e. ignored).

Fixes: af25071c1d ("target/sparc: Move RDASR, STBAR, MEMBAR to decodetree")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3097
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/sparc/translate.c  | 12 +++++++++++-
 target/sparc/insns.decode | 13 ++++++++++++-
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/target/sparc/translate.c b/target/sparc/translate.c
index b922e53bf1..c2ffd965d8 100644
--- a/target/sparc/translate.c
+++ b/target/sparc/translate.c
@@ -2823,12 +2823,22 @@ static bool trans_Tcc_i_v9(DisasContext *dc, arg_Tcc_i_v9 *a)
     return do_tcc(dc, a->cond, a->cc, a->rs1, true, a->i);
 }
 
-static bool trans_STBAR(DisasContext *dc, arg_STBAR *a)
+static bool do_stbar(DisasContext *dc)
 {
     tcg_gen_mb(TCG_MO_ST_ST | TCG_BAR_SC);
     return advance_pc(dc);
 }
 
+static bool trans_STBAR_v8(DisasContext *dc, arg_STBAR_v8 *a)
+{
+    return avail_32(dc) && do_stbar(dc);
+}
+
+static bool trans_STBAR_v9(DisasContext *dc, arg_STBAR_v9 *a)
+{
+    return avail_64(dc) && do_stbar(dc);
+}
+
 static bool trans_MEMBAR(DisasContext *dc, arg_MEMBAR *a)
 {
     if (avail_32(dc)) {
diff --git a/target/sparc/insns.decode b/target/sparc/insns.decode
index 9e39d23273..1b1b85e9c2 100644
--- a/target/sparc/insns.decode
+++ b/target/sparc/insns.decode
@@ -88,7 +88,7 @@ CALL    01 i:s30
 
 {
   [
-    STBAR           10 00000 101000 01111 0 0000000000000
+    STBAR_v9        10 00000 101000 01111 0 0000000000000
     MEMBAR          10 00000 101000 01111 1 000000 cmask:3 mmask:4
 
     RDCCR           10 rd:5  101000 00010 0 0000000000000
@@ -107,6 +107,17 @@ CALL    01 i:s30
     RDSTICK_CMPR    10 rd:5  101000 11001 0 0000000000000
     RDSTRAND_STATUS 10 rd:5  101000 11010 0 0000000000000
   ]
+
+  # The v8 manual, section B.30 STBAR instruction, says
+  # bits [12:0] are ignored, but bit 13 must be 0.
+  # However, section B.28 Read State Register Instruction has a
+  # comment that RDASR with rs1 = 15, rd = 0 is STBAR.  Here,
+  # bit 13 is also ignored and rd != 0 is merely reserved.
+  #
+  # Solaris 8 executes v9 MEMBAR instruction 0x8143e008 during boot.
+  # This confirms that bit 13 is ignored, as 0x8143c000 is STBAR.
+  STBAR_v8          10 ----- 101000 01111 - -------------
+
   # Before v8, all rs1 accepted; otherwise rs1==0.
   RDY               10 rd:5  101000 rs1:5 0 0000000000000
 }
-- 
2.43.0