Add safe vsnprintf and snprintf library functions

From: Sonny Rao <sonnyrao@chromium.org>

These functions are useful in U-Boot because they allow a graceful failure
rather than an unpredictable stack overflow when printf() buffers are
exceeded.

Mostly copied from the Linux kernel. I copied vscnprintf and
scnprintf so we can change printf and vprintf to use the safe
implementation but still return the correct values.

(Simon Glass <sjg@chromium.org> modified this commit a little)

Signed-off-by: Sonny Rao <sonnyrao@chromium.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/README b/README
index 6fe1e0fc2d7..79167777973 100644
--- a/README
+++ b/README
@@ -655,6 +655,15 @@ The following options need to be configured:
 		to get the character out. Baud rates will need to default
 		to something sensible.
 
+- Safe printf() functions
+		Define CONFIG_SYS_VSNPRINTF to compile in safe versions of
+		the printf() functions. These are defined in
+		include/vsprintf.h and include snprintf(), vsnprintf() and
+		so on. Code size increase is approximately 300-500 bytes.
+		If this option is not given then these functions will
+		silently discard their buffer size argument - this means
+		you are not getting any overflow checking in this case.
+
 - Boot Delay:	CONFIG_BOOTDELAY - in seconds
 		Delay before automatically booting the default image;
 		set to -1 to disable autoboot.