tcg: Add tcg_out_tb_start backend hook

This hook may emit code at the beginning of the TB.

Suggested-by: Jordan Niethe <jniethe5@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/aarch64/tcg-target.c.inc

@@ -3135,6 +3135,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_insn(s, 3207, RET, TCG_REG_LR);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_out_nop_fill(tcg_insn_unit *p, int count)
 {
     int i;

tcg/arm/tcg-target.c.inc

@@ -2962,6 +2962,11 @@ static void tcg_out_epilogue(TCGContext *s)
                   (1 << TCG_REG_R10) | (1 << TCG_REG_R11) | (1 << TCG_REG_PC));
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 typedef struct {
     DebugFrameHeader h;
     uint8_t fde_def_cfa[4];

tcg/i386/tcg-target.c.inc

@@ -4191,6 +4191,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_opc(s, OPC_RET, 0, 0, 0);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_out_nop_fill(tcg_insn_unit *p, int count)
 {
     memset(p, 0x90, count);

tcg/loongarch64/tcg-target.c.inc

@@ -2296,6 +2296,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_opc_jirl(s, TCG_REG_ZERO, TCG_REG_RA, 0);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_target_init(TCGContext *s)
 {
     unsigned long hwcap = qemu_getauxval(AT_HWCAP);

tcg/mips/tcg-target.c.inc

@@ -2628,6 +2628,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_opc_reg(s, OPC_OR, TCG_TMP3, TCG_TMP3, TCG_TMP1);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_target_init(TCGContext *s)
 {
     tcg_target_detect_isa();

tcg/ppc/tcg-target.c.inc

@@ -2527,6 +2527,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out32(s, BCLR | BO_ALWAYS);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_out_exit_tb(TCGContext *s, uintptr_t arg)
 {
     tcg_out_movi(s, TCG_TYPE_PTR, TCG_REG_R3, arg);

tcg/riscv/tcg-target.c.inc

@@ -2099,6 +2099,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_opc_imm(s, OPC_JALR, TCG_REG_ZERO, TCG_REG_RA, 0);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static volatile sig_atomic_t got_sigill;
 
 static void sigill_handler(int signo, siginfo_t *si, void *data)

tcg/s390x/tcg-target.c.inc

@@ -3483,6 +3483,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_insn(s, RR, BCR, S390_CC_ALWAYS, TCG_REG_R14);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_out_nop_fill(tcg_insn_unit *p, int count)
 {
     memset(p, 0x07, count * sizeof(tcg_insn_unit));

tcg/sparc64/tcg-target.c.inc

@@ -962,6 +962,11 @@ static void tcg_target_qemu_prologue(TCGContext *s)
     tcg_out_movi_s13(s, TCG_REG_O0, 0);
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 static void tcg_out_nop_fill(tcg_insn_unit *p, int count)
 {
     int i;

tcg/tcg.c

@@ -108,6 +108,7 @@ static void tcg_register_jit_int(const void *buf, size_t size,
     __attribute__((unused));
 
 /* Forward declarations for functions declared and used in tcg-target.c.inc. */
+static void tcg_out_tb_start(TCGContext *s);
 static void tcg_out_ld(TCGContext *s, TCGType type, TCGReg ret, TCGReg arg1,
                        intptr_t arg2);
 static bool tcg_out_mov(TCGContext *s, TCGType type, TCGReg ret, TCGReg arg);
@@ -6014,6 +6015,8 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb, uint64_t pc_start)
     s->gen_insn_data =
         tcg_malloc(sizeof(uint64_t) * s->gen_tb->icount * start_words);
 
+    tcg_out_tb_start(s);
+
     num_insns = -1;
     QTAILQ_FOREACH(op, &s->ops, link) {
         TCGOpcode opc = op->opc;

tcg/tci/tcg-target.c.inc

@@ -955,6 +955,11 @@ static inline void tcg_target_qemu_prologue(TCGContext *s)
 {
 }
 
+static void tcg_out_tb_start(TCGContext *s)
+{
+    /* nothing to do */
+}
+
 bool tcg_target_has_memory_bswap(MemOp memop)
 {
     return true;