linux-kernel - [PATCH] lib/hexdump: Make print_hex_dump

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Message-Id: <20190816235624.115280-1-swboyd@chromium.org>
Date:   Fri, 16 Aug 2019 16:56:24 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] lib/hexdump: Make print_hex_dump_bytes() a nop on !DEBUG builds

I'm seeing a bunch of debug prints from a user of print_hex_dump_bytes()
in my kernel logs, but I don't have CONFIG_DYNAMIC_DEBUG enabled nor do
I have DEBUG defined in my build. The problem is that
print_hex_dump_bytes() calls a wrapper function in lib/hexdump.c  that
calls print_hex_dump() with KERN_DEBUG level. There are three cases to
consider here

  1. CONFIG_DYNAMIC_DEBUG=y  --> call dynamic_hex_dum()
  2. CONFIG_DYNAMIC_DEBUG=n && DEBUG --> call print_hex_dump()
  3. CONFIG_DYNAMIC_DEBUG=n && !DEBUG --> stub it out

Right now, that last case isn't detected and we still call
print_hex_dump() from the stub wrapper.

Let's make print_hex_dump_bytes() only call print_hex_dump_debug() so
that it works properly in all cases.

Case #1, print_hex_dump_debug() calls dynamic_hex_dump() and we get same
behavior. Case #2, print_hex_dump_debug() calls print_hex_dump() with
KERN_DEBUG and we get the same behavior. Case #3, print_hex_dump_debug()
is a nop, changing behavior to what we want, i.e. print nothing.

Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 include/linux/printk.h | 22 +++++++++++++++-------
 lib/hexdump.c          | 21 ---------------------
 2 files changed, 15 insertions(+), 28 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index cefd374c47b1..c09d67edda3a 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -488,13 +488,6 @@ extern int hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 extern void print_hex_dump(const char *level, const char *prefix_str,
 			   int prefix_type, int rowsize, int groupsize,
 			   const void *buf, size_t len, bool ascii);
-#if defined(CONFIG_DYNAMIC_DEBUG)
-#define print_hex_dump_bytes(prefix_str, prefix_type, buf, len)	\
-	dynamic_hex_dump(prefix_str, prefix_type, 16, 1, buf, len, true)
-#else
-extern void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
-				 const void *buf, size_t len);
-#endif /* defined(CONFIG_DYNAMIC_DEBUG) */
 #else
 static inline void print_hex_dump(const char *level, const char *prefix_str,
 				  int prefix_type, int rowsize, int groupsize,
@@ -526,4 +519,19 @@ static inline void print_hex_dump_debug(const char *prefix_str, int prefix_type,
 }
 #endif
 
+/**
+ * print_hex_dump_bytes - shorthand form of print_hex_dump() with default params
+ * @prefix_str: string to prefix each line with;
+ *  caller supplies trailing spaces for alignment if desired
+ * @prefix_type: controls whether prefix of an offset, address, or none
+ *  is printed (%DUMP_PREFIX_OFFSET, %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_NONE)
+ * @buf: data blob to dump
+ * @len: number of bytes in the @buf
+ *
+ * Calls print_hex_dump(), with log level of KERN_DEBUG,
+ * rowsize of 16, groupsize of 1, and ASCII output included.
+ */
+#define print_hex_dump_bytes(prefix_str, prefix_type, buf, len)	\
+	print_hex_dump_debug(prefix_str, prefix_type, 16, 1, buf, len, true)
+
 #endif
diff --git a/lib/hexdump.c b/lib/hexdump.c
index b1d55b669ae2..147133f8eb2f 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -270,25 +270,4 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
 }
 EXPORT_SYMBOL(print_hex_dump);
 
-#if !defined(CONFIG_DYNAMIC_DEBUG)
-/**
- * print_hex_dump_bytes - shorthand form of print_hex_dump() with default params
- * @prefix_str: string to prefix each line with;
- *  caller supplies trailing spaces for alignment if desired
- * @prefix_type: controls whether prefix of an offset, address, or none
- *  is printed (%DUMP_PREFIX_OFFSET, %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_NONE)
- * @buf: data blob to dump
- * @len: number of bytes in the @buf
- *
- * Calls print_hex_dump(), with log level of KERN_DEBUG,
- * rowsize of 16, groupsize of 1, and ASCII output included.
- */
-void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
-			  const void *buf, size_t len)
-{
-	print_hex_dump(KERN_DEBUG, prefix_str, prefix_type, 16, 1,
-		       buf, len, true);
-}
-EXPORT_SYMBOL(print_hex_dump_bytes);
-#endif /* !defined(CONFIG_DYNAMIC_DEBUG) */
 #endif /* defined(CONFIG_PRINTK) */
-- 
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