Changeset 5203efb1 in mainline for kernel/arch/mips32/src/debug/stacktrace.c

Timestamp:

2010-09-12T07:56:18Z (14 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

553f430, dc94cb2

Parents:

2fa10f6 (diff), 76e1121f (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.

Message:

Merge from lp:~jakub/helenos/upa

File:

• kernel/arch/mips32/src/debug/stacktrace.c (modified) (5 diffs)

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.
  */
 
@@ -96 +124 @@
 extern char ktext_end;
 
+static bool bounds_check(uintptr_t pc)
+{
+        return (pc >= (uintptr_t) &ktext_start) &&
+            (pc < (uintptr_t) &ktext_end);
+}
+
 static bool
 scan(stack_trace_context_t *ctx, uintptr_t *prev_fp, uintptr_t *prev_ra)
@@ -106 +140 @@
         do {
                 inst--;
+                if (!bounds_check((uintptr_t) inst))
+                        return false;
 #if 0
                 /*
@@ -180 +216 @@
                                         return false;
                                 /* too big offsets are suspicious */
-                                if (offset > 32 * 4)
+                                if ((size_t) offset > sizeof(istate_t))
                                         return false;
 
@@ -207 +243 @@
 {
         return !((ctx->fp == 0) || ((ctx->fp % 8) != 0) ||
-            (ctx->pc % 4 != 0) || (ctx->pc < (uintptr_t) &ktext_start) ||
-            (ctx->pc >= (uintptr_t) &ktext_end));
+            (ctx->pc % 4 != 0) || !bounds_check(ctx->pc));
 }