tcg: Reduce max TB opcode count

Also, assert that we don't overflow any of two different offsets into
the TB. Both unwind and goto_tb both record a uint16_t for later use.

This fixes an arm-softmmu test case utilizing NEON in which there is
a TB generated that runs to 7800 opcodes, and compiles to 96k on an
x86_64 host.  This overflows the 16-bit offset in which we record the
goto_tb reset offset.  Because of that overflow, we install a jump
destination that goes to neverland.  Boom.

With this reduced op count, the same TB compiles to about 48k for
aarch64, ppc64le, and x86_64 hosts, and neither assertion fires.

Cc: qemu-stable@nongnu.org
Reported-by: "Jason A. Donenfeld" <Jason@zx2c4.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/tcg/ppc/tcg-target.inc.c b/tcg/ppc/tcg-target.inc.c
index 86f7de5..c2f729e 100644
--- a/tcg/ppc/tcg-target.inc.c
+++ b/tcg/ppc/tcg-target.inc.c
@@ -2025,10 +2025,10 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc, const TCGArg *args,
         }
         tcg_out32(s, MTSPR | RS(TCG_REG_TB) | CTR);
         tcg_out32(s, BCCTR | BO_ALWAYS);
-        s->tb_jmp_reset_offset[args[0]] = c = tcg_current_code_size(s);
+        set_jmp_reset_offset(s, args[0]);
         if (USE_REG_TB) {
             /* For the unlinked case, need to reset TCG_REG_TB.  */
-            c = -c;
+            c = -tcg_current_code_size(s);
             assert(c == (int16_t)c);
             tcg_out32(s, ADDI | TAI(TCG_REG_TB, TCG_REG_TB, c));
         }