From f64d04c042193183c6dad98944ae2861b998e8b7 Mon Sep 17 00:00:00 2001
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Date: Fri, 11 Sep 2009 10:28:59 +0200
Subject: [PATCH] [S390] s390dbf: Add description for usage of "%s" in sprintf
events
Using "%s" in sprintf event functions is dangerous. This patch adds a short
description for this issue to the s390 debug feature documentation.
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
Documentation/s390/s390dbf.txt | 7 +++++++
arch/s390/include/asm/debug.h | 9 ++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/Documentation/s390/s390dbf.txt b/Documentation/s390/s390dbf.txt
index 2d10053dd97ea..ae66f9b90a25d 100644
--- a/Documentation/s390/s390dbf.txt
+++ b/Documentation/s390/s390dbf.txt
@@ -495,6 +495,13 @@ and for each vararg a long value. So e.g. for a debug entry with a format
string plus two varargs one would need to allocate a (3 * sizeof(long))
byte data area in the debug_register() function.
+IMPORTANT: Using "%s" in sprintf event functions is dangerous. You can only
+use "%s" in the sprintf event functions, if the memory for the passed string is
+available as long as the debug feature exists. The reason behind this is that
+due to performance considerations only a pointer to the string is stored in
+the debug feature. If you log a string that is freed afterwards, you will get
+an OOPS when inspecting the debug feature, because then the debug feature will
+access the already freed memory.
NOTE: If using the sprintf view do NOT use other event/exception functions
than the sprintf-event and -exception functions.
diff --git a/arch/s390/include/asm/debug.h b/arch/s390/include/asm/debug.h
index 31ed5686a968d..18124b75a7ab3 100644
--- a/arch/s390/include/asm/debug.h
+++ b/arch/s390/include/asm/debug.h
@@ -167,6 +167,10 @@ debug_text_event(debug_info_t* id, int level, const char* txt)
return debug_event_common(id,level,txt,strlen(txt));
}
+/*
+ * IMPORTANT: Use "%s" in sprintf format strings with care! Only pointers are
+ * stored in the s390dbf. See Documentation/s390/s390dbf.txt for more details!
+ */
extern debug_entry_t *
debug_sprintf_event(debug_info_t* id,int level,char *string,...)
__attribute__ ((format(printf, 3, 4)));
@@ -206,7 +210,10 @@ debug_text_exception(debug_info_t* id, int level, const char* txt)
return debug_exception_common(id,level,txt,strlen(txt));
}
-
+/*
+ * IMPORTANT: Use "%s" in sprintf format strings with care! Only pointers are
+ * stored in the s390dbf. See Documentation/s390/s390dbf.txt for more details!
+ */
extern debug_entry_t *
debug_sprintf_exception(debug_info_t* id,int level,char *string,...)
__attribute__ ((format(printf, 3, 4)));
--
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