kbuild: Fix compiler warning with assertion when calling 'fwrite'

Reinhard Tartler discovered a corner case of calling xfwrite() where the
length of the string is zero.

Arnaud Lacombe suggested to use assertion for the corner case, as
fwrite(3) is currently used:

 1) in comment printers. Empty comment are not allowed.
 2) in a callback passed to expr_print(), where the string printed is
    either NULL OR non-empty.
 3) in the lexer, auto-generated, and unused.

I feel using assertion is a good solution:

 1) It cleanly takes care of the above-mentioned corner case.
 2) It can be easily disabled by defining NDEBUG.
 3) It asserts xfwrite() is simply a wrapper for fwrite().

Reported-by: Reinhard Tartler <Reinhard.Tartler@informatik.uni-erlangen.de>
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>

diff --git a/config/expr.h b/config/expr.h
index 80fce57080cc36787e01efc00fe8a111efa3d0ff..d4ecce8bc3a689daa2157e4f47e65e7c62192bd4 100644 (file)
--- a/config/expr.h
+++ b/config/expr.h
@@ -10,6 +10,7 @@
 extern "C" {
 #endif
 
+#include <assert.h>
 #include <stdio.h>
 #ifndef __cplusplus
 #include <stdbool.h>

diff --git a/config/lkc.h b/config/lkc.h
index b633bdb9f3d47c815be8727b155471167135626a..c18f2bd9c095510d1d5e58575b265bd67ae9e781 100644 (file)
--- a/config/lkc.h
+++ b/config/lkc.h
@@ -90,8 +90,10 @@ struct conf_printer {
 /* confdata.c and expr.c */
 static inline void xfwrite(const void *str, size_t len, size_t count, FILE *out)
 {
-       if (fwrite(str, len, count, out) < count)
-               fprintf(stderr, "\nError in writing or end of file.\n");
+       assert(len != 0);
+
+       if (fwrite(str, len, count, out) != count)
+               fprintf(stderr, "Error in writing or end of file.\n");
 }
 
 /* menu.c */