tcg: Always enable TCGv type checking

[qemu.git] / tcg / README

diff --git a/tcg/README b/tcg/README
index 063aeb95eadefbb52762135b2f71969787e32397..a550ff176da28fa3b75657cef16262b193e830ff 100644 (file)
--- a/tcg/README
+++ b/tcg/README
@@ -36,6 +36,12 @@ or a memory location which is stored in a register outside QEMU TBs
 A TCG "basic block" corresponds to a list of instructions terminated
 by a branch instruction. 
 
+An operation with "undefined behavior" may result in a crash.
+
+An operation with "unspecified behavior" shall not crash.  However,
+the result may be one of several possibilities so may be considered
+an "undefined result".
+
 3) Intermediate representation
 
 3.1) Introduction
@@ -239,23 +245,25 @@ t0=t1|~t2
 
 * shl_i32/i64 t0, t1, t2
 
-t0=t1 << t2. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+t0=t1 << t2. Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
 
 * shr_i32/i64 t0, t1, t2
 
-t0=t1 >> t2 (unsigned). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+t0=t1 >> t2 (unsigned). Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
 
 * sar_i32/i64 t0, t1, t2
 
-t0=t1 >> t2 (signed). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+t0=t1 >> t2 (signed). Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
 
 * rotl_i32/i64 t0, t1, t2
 
-Rotation of t2 bits to the left. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+Rotation of t2 bits to the left.
+Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
 
 * rotr_i32/i64 t0, t1, t2
 
-Rotation of t2 bits to the right. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+Rotation of t2 bits to the right.
+Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
 
 ********* Misc
 
@@ -306,6 +314,11 @@ This operation would be equivalent to
 
   dest = (t1 & ~0x0f00) | ((t2 << 8) & 0x0f00)
 
+* trunc_shr_i32 t0, t1, pos
+
+For 64-bit hosts only, right shift the 64-bit input T1 by POS and
+truncate to 32-bit output T0.  Depending on the host, this may be
+a simple mov/shift, or may require additional canonicalization.
 
 ********* Conditional moves
 
@@ -412,30 +425,25 @@ current TB was linked to this TB. Otherwise execute the next
 instructions. Only indices 0 and 1 are valid and tcg_gen_goto_tb may be issued
 at most once with each slot index per TB.
 
-* qemu_ld8u t0, t1, flags
-qemu_ld8s t0, t1, flags
-qemu_ld16u t0, t1, flags
-qemu_ld16s t0, t1, flags
-qemu_ld32 t0, t1, flags
-qemu_ld32u t0, t1, flags
-qemu_ld32s t0, t1, flags
-qemu_ld64 t0, t1, flags
-
-Load data at the QEMU CPU address t1 into t0. t1 has the QEMU CPU address
-type. 'flags' contains the QEMU memory index (selects user or kernel access)
-for example.
-
-Note that "qemu_ld32" implies a 32-bit result, while "qemu_ld32u" and
-"qemu_ld32s" imply a 64-bit result appropriately extended from 32 bits.
-
-* qemu_st8 t0, t1, flags
-qemu_st16 t0, t1, flags
-qemu_st32 t0, t1, flags
-qemu_st64 t0, t1, flags
-
-Store the data t0 at the QEMU CPU Address t1. t1 has the QEMU CPU
-address type. 'flags' contains the QEMU memory index (selects user or
-kernel access) for example.
+* qemu_ld_i32/i64 t0, t1, flags, memidx
+* qemu_st_i32/i64 t0, t1, flags, memidx
+
+Load data at the guest address t1 into t0, or store data in t0 at guest
+address t1.  The _i32/_i64 size applies to the size of the input/output
+register t0 only.  The address t1 is always sized according to the guest,
+and the width of the memory operation is controlled by flags.
+
+Both t0 and t1 may be split into little-endian ordered pairs of registers
+if dealing with 64-bit quantities on a 32-bit host.
+
+The memidx selects the qemu tlb index to use (e.g. user or kernel access).
+The flags are the TCGMemOp bits, selecting the sign, width, and endianness
+of the memory access.
+
+For a 32-bit host, qemu_ld/st_i64 is guaranteed to only be used with a
+64-bit memory access specified in flags.
+
+*********
 
 Note 1: Some shortcuts are defined when the last operand is known to be
 a constant (e.g. addi for add, movi for mov).