Changeset 76e1121f in mainline

Timestamp:

2010-09-04T12:21:05Z (14 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

4687a26c, 5203efb1

Parents:

343f2b7e

Message:

Add an explanatory comment to mips32 stacktrace.c.

File:

• kernel/arch/mips32/src/debug/stacktrace.c (modified) (1 diff)

kernel/arch/mips32/src/debug/stacktrace.c

@@ -31 +31 @@
  */
 /** @file
+ */
+
+/*
+ * This stack tracing code is based on the suggested algorithm described on page
+ * 3-27 and 3-28 of:
+ * 
+ * SYSTEM V
+ * APPLICATION BINARY INTERFACE
+ *
+ * MIPS RISC Processor
+ * Supplement
+ * 3rd Edition
+ *
+ * Unfortunately, GCC generates code which is not entirely compliant with this
+ * method. For example, it places the "jr ra" instruction quite arbitrarily in
+ * the middle of the function which makes the original algorithm unapplicable.
+ *
+ * We deal with this problem by simply not using those parts of the algorithm
+ * that rely on the "jr ra" instruction occurring in the last basic block of a
+ * function, which gives us still usable, but less reliable stack tracer. The
+ * unreliability stems from the fact that under some circumstances it can become
+ * confused and produce incorrect or incomplete stack trace. We apply extra
+ * sanity checks so that the algorithm is still safe and should not crash the
+ * system.
+ *
+ * Even though not perfect, our solution is pretty lightweight, especially when
+ * compared with a prospective alternative solution based on additional
+ * debugging information stored directly in the kernel image.
  */