3 files changed, 38 insertions, 2 deletions

diff --git a/sys/amd64/include/db_machdep.h b/sys/amd64/include/db_machdep.h
index dae26d79371d8..633f4f3e3bb11 100644
--- a/sys/amd64/include/db_machdep.h
+++ b/sys/amd64/include/db_machdep.h
@@ -73,4 +73,19 @@ extern db_regs_t	ddb_regs;	/* register state */
 #define inst_load(ins)		0
 #define inst_store(ins)		0
 
+/*
+ * There no interesting addresses below _kstack = 0xefbfe000.  There
+ * are small absolute values for GUPROF, but we don't want to see them.
+ * Treat "negative" addresses below _kstack as non-small to allow for
+ * future reductions of _kstack and to avoid sign extension problems.
+ *
+ * There is one interesting symbol above -db_maxoff = 0xffff0000,
+ * namely _APTD = 0xfffff000.  Accepting this would mess up the
+ * printing of small negative offsets.  The next largest symbol is
+ * _APTmap = 0xffc00000.  Accepting this is OK (unless db_maxoff is
+ * set to >= 0x400000 - (max stack offset)).
+ */
+#define	DB_SMALL_VALUE_MAX	0x7fffffff
+#define	DB_SMALL_VALUE_MIN	(-0x400001)
+
 #endif /* !_MACHINE_DB_MACHDEP_H_ */
diff --git a/sys/ddb/db_sym.c b/sys/ddb/db_sym.c
index 0afa48abe783f..7974825758a27 100644
--- a/sys/ddb/db_sym.c
+++ b/sys/ddb/db_sym.c
@@ -274,7 +274,7 @@ db_symbol_values(sym, namep, valuep)
  * then we just print the value in hex.  Small values might get
  * bogus symbol associations, e.g. 3 might get some absolute
  * value like _INCLUDE_VERSION or something, therefore we do
- * not accept symbols whose value is zero (and use plain hex).
+ * not accept symbols whose value is "small" (and use plain hex).
  */
 
 unsigned int	db_maxoff = 0x10000;
@@ -293,7 +293,13 @@ db_printsym(off, strategy)
 
 	cursym = db_search_symbol(off, strategy, &d);
 	db_symbol_values(cursym, &name, &value);
-	if (name == 0 || d >= db_maxoff || value == 0) {
+	if (name == 0)
+		value = off;
+	if (value >= DB_SMALL_VALUE_MIN && value <= DB_SMALL_VALUE_MAX) {
+		db_printf("%+#n", off);
+		return;
+	}
+	if (name == 0 || d >= db_maxoff) {
 		db_printf("%#n", off);
 		return;
 	}
diff --git a/sys/i386/include/db_machdep.h b/sys/i386/include/db_machdep.h
index dae26d79371d8..633f4f3e3bb11 100644
--- a/sys/i386/include/db_machdep.h
+++ b/sys/i386/include/db_machdep.h
@@ -73,4 +73,19 @@ extern db_regs_t	ddb_regs;	/* register state */
 #define inst_load(ins)		0
 #define inst_store(ins)		0
 
+/*
+ * There no interesting addresses below _kstack = 0xefbfe000.  There
+ * are small absolute values for GUPROF, but we don't want to see them.
+ * Treat "negative" addresses below _kstack as non-small to allow for
+ * future reductions of _kstack and to avoid sign extension problems.
+ *
+ * There is one interesting symbol above -db_maxoff = 0xffff0000,
+ * namely _APTD = 0xfffff000.  Accepting this would mess up the
+ * printing of small negative offsets.  The next largest symbol is
+ * _APTmap = 0xffc00000.  Accepting this is OK (unless db_maxoff is
+ * set to >= 0x400000 - (max stack offset)).
+ */
+#define	DB_SMALL_VALUE_MAX	0x7fffffff
+#define	DB_SMALL_VALUE_MIN	(-0x400001)
+
 #endif /* !_MACHINE_DB_MACHDEP_H_ */