[PATCH 16/22] tcg/aarch64: Reorg goto_tb implementation

[Richard Henderson]

The old implementation replaces two insns, swapping between

        b       <dest>
        nop
        br      x30
and
        adrp    x30, <dest>
        addi    x30, x30, lo12:<dest>
        br      x30

There is a race condition in which a thread could be stopped at
the PC of the second insn, and when restarted does not see the
complete address computation and branches to nowhere.

The new implemetation replaces only one insn, swapping between

        b       <dest>
        br      tmp
and
        ldr     tmp, <jmp_addr>
        br      tmp

Reported-by: hev <r@hev.cc>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/aarch64/tcg-target.h     |  2 +-
 tcg/aarch64/tcg-target.c.inc | 64 +++++++++++++++---------------------
 2 files changed, 27 insertions(+), 39 deletions(-)

diff --git a/tcg/aarch64/tcg-target.h b/tcg/aarch64/tcg-target.h
index c8202e4bc5..9b8835eaa3 100644
--- a/tcg/aarch64/tcg-target.h
+++ b/tcg/aarch64/tcg-target.h
@@ -15,7 +15,7 @@
 
 #define TCG_TARGET_INSN_UNIT_SIZE  4
 #define TCG_TARGET_TLB_DISPLACEMENT_BITS 24
-#define MAX_CODE_GEN_BUFFER_SIZE  (2 * GiB)
+#define MAX_CODE_GEN_BUFFER_SIZE  ((size_t)-1)
 #undef TCG_TARGET_STACK_GROWSUP
 
 typedef enum {
diff --git a/tcg/aarch64/tcg-target.c.inc b/tcg/aarch64/tcg-target.c.inc
index af30f9db69..fe8e8636aa 100644
--- a/tcg/aarch64/tcg-target.c.inc
+++ b/tcg/aarch64/tcg-target.c.inc
@@ -1352,33 +1352,6 @@ static void tcg_out_call(TCGContext *s, const 
tcg_insn_unit *target)
     }
 }
 
-void tb_target_set_jmp_target(const TranslationBlock *tb, int n,
-                              uintptr_t jmp_rx, uintptr_t jmp_rw)
-{
-    uintptr_t addr = tb->jmp_target_addr[n];
-    tcg_insn_unit i1, i2;
-    TCGType rt = TCG_TYPE_I64;
-    TCGReg  rd = TCG_REG_TMP;
-    uint64_t pair;
-
-    ptrdiff_t offset = addr - jmp_rx;
-
-    if (offset == sextract64(offset, 0, 26)) {
-        i1 = I3206_B | ((offset >> 2) & 0x3ffffff);
-        i2 = NOP;
-    } else {
-        offset = (addr >> 12) - (jmp_rx >> 12);
-
-        /* patch ADRP */
-        i1 = I3406_ADRP | (offset & 3) << 29 | (offset & 0x1ffffc) << (5 - 2) 
| rd;
-        /* patch ADDI */
-        i2 = I3401_ADDI | rt << 31 | (addr & 0xfff) << 10 | rd << 5 | rd;
-    }
-    pair = (uint64_t)i2 << 32 | i1;
-    qatomic_set((uint64_t *)jmp_rw, pair);
-    flush_idcache_range(jmp_rx, jmp_rw, 8);
-}
-
 static inline void tcg_out_goto_label(TCGContext *s, TCGLabel *l)
 {
     if (!l->has_value) {
@@ -1901,23 +1874,38 @@ static void tcg_out_exit_tb(TCGContext *s, uintptr_t a0)
 static void tcg_out_goto_tb(TCGContext *s, int which)
 {
     /*
-     * Ensure that ADRP+ADD are 8-byte aligned so that an atomic
-     * write can be used to patch the target address.
+     * Direct branch, or indirect address load, will be patched
+     * by tb_target_set_jmp_target.  Assert indirect load offset
+     * in range early, regardless of direct branch distance.
      */
-    if ((uintptr_t)s->code_ptr & 7) {
-        tcg_out32(s, NOP);
-    }
+    intptr_t i_off = tcg_pcrel_diff(s, (void *)get_jmp_target_addr(s, which));
+    tcg_debug_assert(i_off == sextract64(i_off, 0, 21));
+
     set_jmp_insn_offset(s, which);
-    /*
-     * actual branch destination will be patched by
-     * tb_target_set_jmp_target later
-     */
-    tcg_out_insn(s, 3406, ADRP, TCG_REG_TMP, 0);
-    tcg_out_insn(s, 3401, ADDI, TCG_TYPE_I64, TCG_REG_TMP, TCG_REG_TMP, 0);
+    tcg_out32(s, I3206_B);
     tcg_out_insn(s, 3207, BR, TCG_REG_TMP);
     set_jmp_reset_offset(s, which);
 }
 
+void tb_target_set_jmp_target(const TranslationBlock *tb, int n,
+                              uintptr_t jmp_rx, uintptr_t jmp_rw)
+{
+    uintptr_t d_addr = tb->jmp_target_addr[n];
+    uintptr_t i_addr = (uintptr_t)&tb->jmp_target_addr[n];
+    ptrdiff_t d_offset = d_addr - jmp_rx;
+    ptrdiff_t i_offset = i_addr - jmp_rx;
+    tcg_insn_unit insn;
+
+    /* Either directly branch, or indirect branch load. */
+    if (d_offset == sextract64(d_offset, 0, 26)) {
+        insn = I3206_B | ((d_offset >> 2) & 0x3ffffff);
+    } else {
+        insn = I3305_LDR | TCG_REG_TMP | (((i_offset >> 2) & 0x7ffff) << 5);
+    }
+    qatomic_set((uint32_t *)jmp_rw, insn);
+    flush_idcache_range(jmp_rx, jmp_rw, 4);
+}
+
 static void tcg_out_op(TCGContext *s, TCGOpcode opc,
                        const TCGArg args[TCG_MAX_OP_ARGS],
                        const int const_args[TCG_MAX_OP_ARGS])
-- 
2.34.1