tcg/arm: Fix broken CONFIG_TCG_PASS_AREG0 code

The CONFIG_TCG_PASS_AREG0 code for calling ld/st helpers was
broken in that it did not respect the ABI requirement that 64
bit values were passed in even-odd register pairs. The simplest
way to fix this is to implement some new utility functions
for marshalling function arguments into the correct registers
and stack, so that the code which sets up the address and
data arguments does not need to care whether there has been
a preceding env argument.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

tcg/arm/tcg-target.c

@@ -176,6 +176,13 @@ static int target_parse_constraint(TCGArgConstraint *ct, const char **pct_str)
            so don't use these. */
         tcg_regset_reset_reg(ct->u.regs, TCG_REG_R0);
         tcg_regset_reset_reg(ct->u.regs, TCG_REG_R1);
+#if defined(CONFIG_TCG_PASS_AREG0) && (TARGET_LONG_BITS == 64)
+        /* If we're passing env to the helper as r0 and need a regpair
+         * for the address then r2 will be overwritten as we're setting
+         * up the args to the helper.
+         */
+        tcg_regset_reset_reg(ct->u.regs, TCG_REG_R2);
+#endif
 #endif
         break;
     case 'L':
@@ -197,6 +204,12 @@ static int target_parse_constraint(TCGArgConstraint *ct, const char **pct_str)
            use these. */
         tcg_regset_reset_reg(ct->u.regs, TCG_REG_R0);
         tcg_regset_reset_reg(ct->u.regs, TCG_REG_R1);
+#if defined(CONFIG_SOFTMMU) && \
+    defined(CONFIG_TCG_PASS_AREG0) && (TARGET_LONG_BITS == 64)
+        /* Avoid clashes with registers being used for helper args */
+        tcg_regset_reset_reg(ct->u.regs, TCG_REG_R2);
+        tcg_regset_reset_reg(ct->u.regs, TCG_REG_R3);
+#endif
         break;
     /* qemu_st64 data_reg2 */
     case 'S':
@@ -210,6 +223,10 @@ static int target_parse_constraint(TCGArgConstraint *ct, const char **pct_str)
 #ifdef CONFIG_SOFTMMU
         /* r2 is still needed to load data_reg, so don't use it. */
         tcg_regset_reset_reg(ct->u.regs, TCG_REG_R2);
+#if defined(CONFIG_TCG_PASS_AREG0) && (TARGET_LONG_BITS == 64)
+        /* Avoid clashes with registers being used for helper args */
+        tcg_regset_reset_reg(ct->u.regs, TCG_REG_R3);
+#endif
 #endif
         break;
 
@@ -388,6 +405,14 @@ static inline void tcg_out_dat_reg(TCGContext *s,
                     (rn << 16) | (rd << 12) | shift | rm);
 }
 
+static inline void tcg_out_mov_reg(TCGContext *s, int cond, int rd, int rm)
+{
+    /* Simple reg-reg move, optimising out the 'do nothing' case */
+    if (rd != rm) {
+        tcg_out_dat_reg(s, cond, ARITH_MOV, rd, 0, rm, SHIFT_IMM_LSL(0));
+    }
+}
+
 static inline void tcg_out_dat_reg2(TCGContext *s,
                 int cond, int opc0, int opc1, int rd0, int rd1,
                 int rn0, int rn1, int rm0, int rm1, int shift)
@@ -966,6 +991,90 @@ static void *qemu_st_helpers[4] = {
     __stq_mmu,
 };
 #endif
+
+/* Helper routines for marshalling helper function arguments into
+ * the correct registers and stack.
+ * argreg is where we want to put this argument, arg is the argument itself.
+ * Return value is the updated argreg ready for the next call.
+ * Note that argreg 0..3 is real registers, 4+ on stack.
+ * When we reach the first stacked argument, we allocate space for it
+ * and the following stacked arguments using "str r8, [sp, #-0x10]!".
+ * Following arguments are filled in with "str r8, [sp, #0xNN]".
+ * For more than 4 stacked arguments we'd need to know how much
+ * space to allocate when we pushed the first stacked argument.
+ * We don't need this, so don't implement it (and will assert if you try it.)
+ *
+ * We provide routines for arguments which are: immediate, 32 bit
+ * value in register, 16 and 8 bit values in register (which must be zero
+ * extended before use) and 64 bit value in a lo:hi register pair.
+ */
+#define DEFINE_TCG_OUT_ARG(NAME, ARGPARAM)                                 \
+    static TCGReg NAME(TCGContext *s, TCGReg argreg, ARGPARAM)             \
+    {                                                                      \
+        if (argreg < 4) {                                                  \
+            TCG_OUT_ARG_GET_ARG(argreg);                                   \
+        } else if (argreg == 4) {                                          \
+            TCG_OUT_ARG_GET_ARG(TCG_REG_R8);                               \
+            tcg_out32(s, (COND_AL << 28) | 0x052d8010);                    \
+        } else {                                                           \
+            assert(argreg < 8);                                            \
+            TCG_OUT_ARG_GET_ARG(TCG_REG_R8);                               \
+            tcg_out32(s, (COND_AL << 28) | 0x058d8000 | (argreg - 4) * 4); \
+        }                                                                  \
+        return argreg + 1;                                                 \
+    }
+
+#define TCG_OUT_ARG_GET_ARG(A) tcg_out_dat_imm(s, COND_AL, ARITH_MOV, A, 0, arg)
+DEFINE_TCG_OUT_ARG(tcg_out_arg_imm32, uint32_t arg)
+#undef TCG_OUT_ARG_GET_ARG
+#define TCG_OUT_ARG_GET_ARG(A) tcg_out_ext8u(s, COND_AL, A, arg)
+DEFINE_TCG_OUT_ARG(tcg_out_arg_reg8, TCGReg arg)
+#undef TCG_OUT_ARG_GET_ARG
+#define TCG_OUT_ARG_GET_ARG(A) tcg_out_ext16u(s, COND_AL, A, arg)
+DEFINE_TCG_OUT_ARG(tcg_out_arg_reg16, TCGReg arg)
+#undef TCG_OUT_ARG_GET_ARG
+
+/* We don't use the macro for this one to avoid an unnecessary reg-reg
+ * move when storing to the stack.
+ */
+static TCGReg tcg_out_arg_reg32(TCGContext *s, TCGReg argreg, TCGReg arg)
+{
+    if (argreg < 4) {
+        tcg_out_mov_reg(s, COND_AL, argreg, arg);
+    } else if (argreg == 4) {
+        /* str arg, [sp, #-0x10]! */
+        tcg_out32(s, (COND_AL << 28) | 0x052d0010 | (arg << 12));
+    } else {
+        assert(argreg < 8);
+        /* str arg, [sp, #0xNN] */
+        tcg_out32(s, (COND_AL << 28) | 0x058d0000 |
+                  (arg << 12) | (argreg - 4) * 4);
+    }
+    return argreg + 1;
+}
+
+static inline TCGReg tcg_out_arg_reg64(TCGContext *s, TCGReg argreg,
+                                       TCGReg arglo, TCGReg arghi)
+{
+    /* 64 bit arguments must go in even/odd register pairs
+     * and in 8-aligned stack slots.
+     */
+    if (argreg & 1) {
+        argreg++;
+    }
+    argreg = tcg_out_arg_reg32(s, argreg, arglo);
+    argreg = tcg_out_arg_reg32(s, argreg, arghi);
+    return argreg;
+}
+
+static inline void tcg_out_arg_stacktidy(TCGContext *s, TCGReg argreg)
+{
+    /* Output any necessary post-call cleanup of the stack */
+    if (argreg > 4) {
+        tcg_out_dat_imm(s, COND_AL, ARITH_ADD, TCG_REG_R13, TCG_REG_R13, 0x10);
+    }
+}
+
 #endif
 
 #define TLB_SHIFT	(CPU_TLB_ENTRY_BITS + CPU_TLB_BITS)
@@ -975,6 +1084,7 @@ static inline void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args, int opc)
     int addr_reg, data_reg, data_reg2, bswap;
 #ifdef CONFIG_SOFTMMU
     int mem_index, s_bits;
+    TCGReg argreg;
 # if TARGET_LONG_BITS == 64
     int addr_reg2;
 # endif
@@ -1088,31 +1198,22 @@ static inline void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args, int opc)
     tcg_out_b_noaddr(s, COND_EQ);
 
     /* TODO: move this code to where the constants pool will be */
-    if (addr_reg != TCG_REG_R0) {
+    /* Note that this code relies on the constraints we set in arm_op_defs[]
-        tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
+     * to ensure that later arguments are not passed to us in registers we
-                        TCG_REG_R0, 0, addr_reg, SHIFT_IMM_LSL(0));
+     * trash by moving the earlier arguments into them.
-    }
+     */
-# if TARGET_LONG_BITS == 32
+    argreg = TCG_REG_R0;
-    tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R1, 0, mem_index);
-# else
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    TCG_REG_R1, 0, addr_reg2, SHIFT_IMM_LSL(0));
-    tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R2, 0, mem_index);
-# endif
 #ifdef CONFIG_TCG_PASS_AREG0
-    /* XXX/FIXME: suboptimal and incorrect for 64 bit */
+    argreg = tcg_out_arg_reg32(s, argreg, TCG_AREG0);
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[2], 0,
-                    tcg_target_call_iarg_regs[1], SHIFT_IMM_LSL(0));
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[1], 0,
-                    tcg_target_call_iarg_regs[0], SHIFT_IMM_LSL(0));
-
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[0], 0, TCG_AREG0,
-                    SHIFT_IMM_LSL(0));
 #endif
+#if TARGET_LONG_BITS == 64
+    argreg = tcg_out_arg_reg64(s, argreg, addr_reg, addr_reg2);
+#else
+    argreg = tcg_out_arg_reg32(s, argreg, addr_reg);
+#endif
+    argreg = tcg_out_arg_imm32(s, argreg, mem_index);
     tcg_out_call(s, (tcg_target_long) qemu_ld_helpers[s_bits]);
+    tcg_out_arg_stacktidy(s, argreg);
 
     switch (opc) {
     case 0 | 4:
@@ -1211,6 +1312,7 @@ static inline void tcg_out_qemu_st(TCGContext *s, const TCGArg *args, int opc)
     int addr_reg, data_reg, data_reg2, bswap;
 #ifdef CONFIG_SOFTMMU
     int mem_index, s_bits;
+    TCGReg argreg;
 # if TARGET_LONG_BITS == 64
     int addr_reg2;
 # endif
@@ -1314,89 +1416,38 @@ static inline void tcg_out_qemu_st(TCGContext *s, const TCGArg *args, int opc)
     tcg_out_b_noaddr(s, COND_EQ);
 
     /* TODO: move this code to where the constants pool will be */
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
+    /* Note that this code relies on the constraints we set in arm_op_defs[]
-                    TCG_REG_R0, 0, addr_reg, SHIFT_IMM_LSL(0));
+     * to ensure that later arguments are not passed to us in registers we
-# if TARGET_LONG_BITS == 32
+     * trash by moving the earlier arguments into them.
-    switch (opc) {
+     */
-    case 0:
+    argreg = TCG_REG_R0;
-        tcg_out_ext8u(s, COND_AL, TCG_REG_R1, data_reg);
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R2, 0, mem_index);
-        break;
-    case 1:
-        tcg_out_ext16u(s, COND_AL, TCG_REG_R1, data_reg);
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R2, 0, mem_index);
-        break;
-    case 2:
-        tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                        TCG_REG_R1, 0, data_reg, SHIFT_IMM_LSL(0));
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R2, 0, mem_index);
-        break;
-    case 3:
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R8, 0, mem_index);
-        tcg_out32(s, (COND_AL << 28) | 0x052d8010); /* str r8, [sp, #-0x10]! */
-        if (data_reg != TCG_REG_R2) {
-            tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                            TCG_REG_R2, 0, data_reg, SHIFT_IMM_LSL(0));
-        }
-        if (data_reg2 != TCG_REG_R3) {
-            tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                            TCG_REG_R3, 0, data_reg2, SHIFT_IMM_LSL(0));
-        }
-        break;
-    }
-# else
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    TCG_REG_R1, 0, addr_reg2, SHIFT_IMM_LSL(0));
-    switch (opc) {
-    case 0:
-        tcg_out_ext8u(s, COND_AL, TCG_REG_R2, data_reg);
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R3, 0, mem_index);
-        break;
-    case 1:
-        tcg_out_ext16u(s, COND_AL, TCG_REG_R2, data_reg);
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R3, 0, mem_index);
-        break;
-    case 2:
-        if (data_reg != TCG_REG_R2) {
-            tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                            TCG_REG_R2, 0, data_reg, SHIFT_IMM_LSL(0));
-        }
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R3, 0, mem_index);
-        break;
-    case 3:
-        tcg_out_dat_imm(s, COND_AL, ARITH_MOV, TCG_REG_R8, 0, mem_index);
-        tcg_out32(s, (COND_AL << 28) | 0x052d8010); /* str r8, [sp, #-0x10]! */
-        if (data_reg != TCG_REG_R2) {
-            tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                            TCG_REG_R2, 0, data_reg, SHIFT_IMM_LSL(0));
-        }
-        if (data_reg2 != TCG_REG_R3) {
-            tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                            TCG_REG_R3, 0, data_reg2, SHIFT_IMM_LSL(0));
-        }
-        break;
-    }
-# endif
-
 #ifdef CONFIG_TCG_PASS_AREG0
-    /* XXX/FIXME: suboptimal and incorrect for 64 bit */
+    argreg = tcg_out_arg_reg32(s, argreg, TCG_AREG0);
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[3], 0,
-                    tcg_target_call_iarg_regs[2], SHIFT_IMM_LSL(0));
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[2], 0,
-                    tcg_target_call_iarg_regs[1], SHIFT_IMM_LSL(0));
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[1], 0,
-                    tcg_target_call_iarg_regs[0], SHIFT_IMM_LSL(0));
-
-    tcg_out_dat_reg(s, COND_AL, ARITH_MOV,
-                    tcg_target_call_iarg_regs[0], 0, TCG_AREG0,
-                    SHIFT_IMM_LSL(0));
 #endif
+#if TARGET_LONG_BITS == 64
+    argreg = tcg_out_arg_reg64(s, argreg, addr_reg, addr_reg2);
+#else
+    argreg = tcg_out_arg_reg32(s, argreg, addr_reg);
+#endif
+
+    switch (opc) {
+    case 0:
+        argreg = tcg_out_arg_reg8(s, argreg, data_reg);
+        break;
+    case 1:
+        argreg = tcg_out_arg_reg16(s, argreg, data_reg);
+        break;
+    case 2:
+        argreg = tcg_out_arg_reg32(s, argreg, data_reg);
+        break;
+    case 3:
+        argreg = tcg_out_arg_reg64(s, argreg, data_reg, data_reg2);
+        break;
+    }
+
+    argreg = tcg_out_arg_imm32(s, argreg, mem_index);
     tcg_out_call(s, (tcg_target_long) qemu_st_helpers[s_bits]);
-    if (opc == 3)
+    tcg_out_arg_stacktidy(s, argreg);
-        tcg_out_dat_imm(s, COND_AL, ARITH_ADD, TCG_REG_R13, TCG_REG_R13, 0x10);
 
     reloc_pc24(label_ptr, (tcg_target_long)s->code_ptr);
 #else /* !CONFIG_SOFTMMU */