console: bounds check whenever changing the cursor due to an escape code

[mirror_qemu.git] / tcg / README

diff --git a/tcg/README b/tcg/README
index a18a87ffcd741dcc3ee09121e1294a7764a40535..cfdfd96d0953cda6f8619799f4a0935ea363f6ac 100644 (file)
--- a/tcg/README
+++ b/tcg/README
@@ -285,6 +285,20 @@ the four high order bytes are set to zero.
 Indicate that the value of t0 won't be used later. It is useful to
 force dead code elimination.
 
+* deposit_i32/i64 dest, t1, t2, pos, len
+
+Deposit T2 as a bitfield into T1, placing the result in DEST.
+The bitfield is described by POS/LEN, which are immediate values:
+
+  LEN - the length of the bitfield
+  POS - the position of the first bit, counting from the LSB
+
+For example, pos=8, len=4 indicates a 4-bit field at bit 8.
+This operation would be equivalent to
+
+  dest = (t1 & ~0x0f00) | ((t2 << 8) & 0x0f00)
+
+
 ********* Conditional moves
 
 * setcond_i32/i64 cond, dest, t1, t2
@@ -490,7 +504,15 @@ register.
 - Don't hesitate to use helpers for complicated or seldom used target
   instructions. There is little performance advantage in using TCG to
   implement target instructions taking more than about twenty TCG
-  instructions.
+  instructions. Note that this rule of thumb is more applicable to
+  helpers doing complex logic or arithmetic, where the C compiler has
+  scope to do a good job of optimisation; it is less relevant where
+  the instruction is mostly doing loads and stores, and in those cases
+  inline TCG may still be faster for longer sequences.
+
+- The hard limit on the number of TCG instructions you can generate
+  per target instruction is set by MAX_OP_PER_INSTR in exec-all.h --
+  you cannot exceed this without risking a buffer overrun.
 
 - Use the 'discard' instruction if you know that TCG won't be able to
   prove that a given global is "dead" at a given program point. The