[Qemu-devel] [RFC v3 PATCH 01/14] Introduce TCGOpcode for memory barrier

[Pranith Kumar <bobby.prani@gmail.com>]

This commit introduces the TCGOpcode for memory barrier instruction.

This opcode takes an argument which is the type of memory barrier
which should be generated.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 tcg/README    | 17 +++++++++++++++++
 tcg/tcg-op.c  | 11 +++++++++++
 tcg/tcg-op.h  |  2 ++
 tcg/tcg-opc.h |  2 ++
 tcg/tcg.h     | 14 ++++++++++++++
 5 files changed, 46 insertions(+)

diff --git a/tcg/README b/tcg/README
index ce8beba..1d48aa9 100644
--- a/tcg/README
+++ b/tcg/README
@@ -402,6 +402,23 @@ double-word product T0.  The later is returned in two single-word outputs.
 
 Similar to mulu2, except the two inputs T1 and T2 are signed.
 
+********* Memory Barrier support
+
+* mb <$arg>
+
+Generate a target memory barrier instruction to ensure memory ordering as being
+enforced by a corresponding guest memory barrier instruction. The ordering
+enforced by the backend may be stricter than the ordering required by the guest.
+It cannot be weaker. This opcode takes a constant argument which is required to
+generate the appropriate barrier instruction. The backend should take care to
+emit the target barrier instruction only when necessary i.e., for SMP guests and
+when MTTCG is enabled.
+
+The guest translators should generate this opcode for all guest instructions
+which have ordering side effects.
+
+Please see docs/atomics.txt for more information on memory barriers.
+
 ********* 64-bit guest on 32-bit host support
 
 The following opcodes are internal to TCG.  Thus they are to be implemented by
diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c
index 54c0277..08f7858 100644
--- a/tcg/tcg-op.c
+++ b/tcg/tcg-op.c
@@ -39,6 +39,8 @@ extern TCGv_i32 TCGV_HIGH_link_error(TCGv_i64);
 #define TCGV_HIGH TCGV_HIGH_link_error
 #endif
 
+extern int smp_cpus;
+
 /* Note that this is optimized for sequential allocation during translate.
    Up to and including filling in the forward link immediately.  We'll do
    proper termination of the end of the list after we finish translation.  */
@@ -146,6 +148,15 @@ void tcg_gen_op6(TCGContext *ctx, TCGOpcode opc, TCGArg a1, TCGArg a2,
     tcg_emit_op(ctx, opc, pi);
 }
 
+void tcg_gen_mb(TCGArg mb_type)
+{
+#ifndef CONFIG_USER_ONLY
+    if (qemu_tcg_mttcg_enabled() && smp_cpus > 1) {
+        tcg_gen_op1(&tcg_ctx, INDEX_op_mb, mb_type);
+    }
+#endif
+}
+
 /* 32 bit ops */
 
 void tcg_gen_addi_i32(TCGv_i32 ret, TCGv_i32 arg1, int32_t arg2)
diff --git a/tcg/tcg-op.h b/tcg/tcg-op.h
index f217e80..41890cc 100644
--- a/tcg/tcg-op.h
+++ b/tcg/tcg-op.h
@@ -261,6 +261,8 @@ static inline void tcg_gen_br(TCGLabel *l)
     tcg_gen_op1(&tcg_ctx, INDEX_op_br, label_arg(l));
 }
 
+void tcg_gen_mb(TCGArg a);
+
 /* Helper calls. */
 
 /* 32 bit ops */
diff --git a/tcg/tcg-opc.h b/tcg/tcg-opc.h
index 6d0410c..45528d2 100644
--- a/tcg/tcg-opc.h
+++ b/tcg/tcg-opc.h
@@ -42,6 +42,8 @@ DEF(br, 0, 0, 1, TCG_OPF_BB_END)
 # define IMPL64  TCG_OPF_64BIT
 #endif
 
+DEF(mb, 0, 0, 1, 0)
+
 DEF(mov_i32, 1, 1, 0, TCG_OPF_NOT_PRESENT)
 DEF(movi_i32, 1, 0, 1, TCG_OPF_NOT_PRESENT)
 DEF(setcond_i32, 1, 2, 1, 0)
diff --git a/tcg/tcg.h b/tcg/tcg.h
index db6a062..36feca9 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -408,6 +408,20 @@ static inline intptr_t QEMU_ARTIFICIAL GET_TCGV_PTR(TCGv_ptr t)
 #define TCG_CALL_DUMMY_TCGV     MAKE_TCGV_I32(-1)
 #define TCG_CALL_DUMMY_ARG      ((TCGArg)(-1))
 
+typedef enum {
+    TCG_MO_LD_LD    = 1,
+    TCG_MO_ST_LD    = 2,
+    TCG_MO_LD_ST    = 4,
+    TCG_MO_ST_ST    = 8,
+    TCG_MO_ALL      = 0xF, // OR of all above
+} TCGOrder;
+
+typedef enum {
+    TCG_BAR_ACQ     = 32,
+    TCG_BAR_REL     = 64,
+    TCG_BAR_SC      = 128,
+} TCGBar;
+
 /* Conditions.  Note that these are laid out for easy manipulation by
    the functions below:
      bit 0 is used for inverting;
-- 
2.9.0