README: add a few sections

diff --git a/README b/README
index 42bd90d3e6f09a644fdd78bbac8b4d2bae795cf7..93d97236d1bab68b17e021f16800a15a0fc18438 100644 (file)
--- a/README
+++ b/README
@@ -1,11 +1,21 @@
 ****************************************
-CDSChecker Readme
+ CDSChecker Readme
 ****************************************
 
 Copyright (c) 2013 Regents of the University of California. All rights reserved.
 
 CDSChecker is distributed under the GPL v2.
 
+This README is divided into sections as follows:
+
+ I.    Overview
+ II.   Reading an execution trace
+ A.    References
+
+----------------------------------------
+ I. Overview
+----------------------------------------
+
 CDSChecker compiles as a dynamically-linked shared library by simply running
 'make'. It should compile on Linux and Mac OSX, and has been tested with LLVM
 (clang/clang++) and GCC.
@@ -84,3 +94,98 @@ you can build and run the benchmarks as follows:
   make
   ./run.sh barrier/barrier -y -m 2     # runs barrier test with fairness/memory liveness
   ./bench.sh                           # run all benchmarks twice, with timing results
+
+
+----------------------------------------
+ II. Reading an execution trace
+----------------------------------------
+
+When CDSChecker detects a bug in your program (or when run with the --verbose
+flag), it prints the output of the program run (STDOUT) along with some summary
+trace information. The trace is given as a sequence of lines, where each line
+represents an operation in the execution trace. These lines are ordered by the
+order in which they were run by CDSChecker (i.e., the "execution order"), which
+does not necessarily align with the "order" of the values observed (i.e., the
+modification order and the reads-from relation).
+
+Columns:
+
+ o #: The sequence number within the execution. That is, sequence number "9"
+   means the operation was the 9th operation executed by CDSChecker. Note that
+   this represents the execution order, not necessarily any other order (e.g.,
+   modification order or reads-from).
+
+ o t: The thread number
+
+ o Action type: The type of operation performed
+
+ o MO: The memory-order for this operation (i.e., memory_order_XXX, where XXX is
+   relaxed, release, acquire, rel_acq, or seq_cst)
+
+ o Location: The memory location on which this operation is operating. This is
+   well-defined for atomic write/read/RMW, but other operations are subject to
+   CDSChecker implementation details.
+
+ o Value: For reads/writes/RMW, the value returned by the operation. Note that
+   for RMW, this is the value that is *read*, not the value that was *written*.
+   For other operations, 'value' may have some CDSChecker-internal meaning.
+
+ o Rf: For reads, the sequence number of the operation from which it reads.
+   [Note: If the execution is a partial, infeasible trace (labeled INFEASIBLE),
+   as printed during --verbose execution, reads may not be resolved and so may
+   have Rf=? or Rf=Px, where x is a promised future value.]
+
+ o CV: The clock vector, encapsulating the happens-before relation (see our
+   paper, or the C/C++ memory model itself). We use a Lamport-style clock vector
+   similar to [1]. The "clock" is just the sequence number (#). The clock vector
+   can be read as follows:
+
+   Each entry is indexed as CV[i], where
+
+     i = 0, 1, 2, ..., <number of threads>
+
+   So for any thread i, we say CV[i] is the sequence number of the most recent
+   operation in thread i such that operation i happens-before this operation.
+   Notably, thread 0 is reserved as a dummy thread for certain CDSChecker
+   operations.
+
+See the following example trace:
+
+------------------------------------------------------------------------------------
+#    t    Action type     MO       Location         Value               Rf  CV
+------------------------------------------------------------------------------------
+1    1    thread start    seq_cst  0x7f68ff11e7c0   0xdeadbeef              ( 0,  1)
+2    1    init atomic     relaxed        0x601068   0                       ( 0,  2)
+3    1    init atomic     relaxed        0x60106c   0                       ( 0,  3)
+4    1    thread create   seq_cst  0x7f68fe51c710   0x7f68fe51c6e0          ( 0,  4)
+5    2    thread start    seq_cst  0x7f68ff11ebc0   0xdeadbeef              ( 0,  4,  5)
+6    2    atomic read     relaxed        0x60106c   0                   3   ( 0,  4,  6)
+7    1    thread create   seq_cst  0x7f68fe51c720   0x7f68fe51c6e0          ( 0,  7)
+8    3    thread start    seq_cst  0x7f68ff11efc0   0xdeadbeef              ( 0,  7,  0,  8)
+9    2    atomic write    relaxed        0x601068   0                       ( 0,  4,  9)
+10   3    atomic read     relaxed        0x601068   0                   2   ( 0,  7,  0, 10)
+11   2    thread finish   seq_cst  0x7f68ff11ebc0   0xdeadbeef              ( 0,  4, 11)
+12   3    atomic write    relaxed        0x60106c   0x2a                    ( 0,  7,  0, 12)
+13   1    thread join     seq_cst  0x7f68ff11ebc0   0x2                     ( 0, 13, 11)
+14   3    thread finish   seq_cst  0x7f68ff11efc0   0xdeadbeef              ( 0,  7,  0, 14)
+15   1    thread join     seq_cst  0x7f68ff11efc0   0x3                     ( 0, 15, 11, 14)
+16   1    thread finish   seq_cst  0x7f68ff11e7c0   0xdeadbeef              ( 0, 16, 11, 14)
+HASH 4073708854
+------------------------------------------------------------------------------------
+
+Now consider, for example, operation 10:
+
+This is the 10th operation in the execution order. It is an atomic read-relaxed
+operation performed by thread 3 at memory address 0x601068. It reads the value
+"0", which was written by the 2nd operation in the execution order. Its clock
+vector consists of the following values:
+
+  CV[0] = 0, CV[1] = 7, CV[2] = 0, CV[3] = 10
+
+
+----------------------------------------
+ A. References
+----------------------------------------
+
+[1] L. Lamport. Time, clocks, and the ordering of events in a distributed
+    system. CACM, 21(7):558–565, July 1978.