libdrgn: mark log format as non-NULL and disable -Wformat-zero-length

In my branch for the module API (#332), I want to log an error without any additional context. Passing an empty format string causes a "zero-length gnu_printf format string" warning from GCC, and passing NULL crashes in vsnprintf(). Empty format strings are totally valid, but NULL clearly isn't, so annotate the format parameter as non-NULL and disable -Wformat-zero-length. Signed-off-by: Omar Sandoval <[email protected]>
osandov · Oct 9, 2023 · 1009271 · 1009271
1 parent aefe704
commit 1009271
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diff --git a/libdrgn/configure.ac b/libdrgn/configure.ac
@@ -113,6 +113,7 @@ AS_IF([test "x$enable_compiler_warnings" != xno],
        -Wimplicit-fallthrough dnl
        -Wmissing-prototypes dnl
        -Wvla dnl
+       -Wno-format-zero-length dnl
        ], [WARN_CFLAGS], [$compiler_flags_test])])
 AS_IF([test "x$enable_compiler_warnings" = xerror],
       [AX_APPEND_FLAG([-Werror], [WARN_CFLAGS])])

diff --git a/libdrgn/log.h b/libdrgn/log.h
@@ -67,7 +67,7 @@ void drgn_log(enum drgn_log_level level, struct drgn_program *prog,
 /**
  * Log a printf-style message followed by a @ref drgn_error at the given level.
  */
-__attribute__((__format__(__printf__, 4, 5)))
+__attribute__((__format__(__printf__, 4, 5), __nonnull__(2, 4)))
 void drgn_error_log(enum drgn_log_level level, struct drgn_program *prog,
 		    struct drgn_error *err, const char *format, ...);
 /** Log a critical message followed by a @ref drgn_error. */