Fix CentOS 6 build.

Author: wb2osz

CMakeLists.txt

@@ -151,15 +151,35 @@ endif()
 
 if (C_CLANG OR C_GCC)
   # _BSD_SOURCE is deprecated we need to use _DEFAULT_SOURCE.
-  # That might be the case for a more modern compiler but it is still needed
-  # for CentOS 6 & 7.  Without -D_BSD_SOURCE, we get Warning: Implicit declaration of
+  #
+  # That works find for more modern compilers but we have issues with:
+  #	Centos 7, gcc 4.8.5, glibc 2.17
+  #	Centos 6, gcc 4.4.7, glibc 2.12
+  #
+  # CentOS 6 & 7:  Without -D_BSD_SOURCE, we get Warning: Implicit declaration of
   # functions alloca, cfmakeraw, scandir, setlinebuf, strcasecmp, strncasecmp, and strsep.
   # When a function (like strsep) returns a pointer, the compiler instead assumes a 32 bit
   # int and sign extends it out to be a 64 bit pointer.  Use the pointer and Kaboom!
   #
-  ### Wextra spews out so much noise a serious problem was not noticed.
+  # CentOS 6: We have additional problem.  Without -D_POSIX_C_SOURCE=199309L, we get
+  # implicit declaration of function clock_gettime and the linker can't find it.
+  #
+  # It turns out that -D_GNU_SOURCE can be used instead of both of those.  For more information, 
+  # see https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html
+  #
+  # Why was this not an issue before?  If gcc is used without the -std=c99 option, 
+  # it is perfectly happy with clock_gettime, strsep, etc. but with the c99 option, it no longer
+  # recognizes a bunch of commonly used functions.  Using _GNU_SOURCE, rather than _DEFAULT_SOURCE
+  # solves the problem for CentOS 6 & 7.  This also makes -D_XOPEN_SOURCE= unnecessary.
+  # I hope it doesn't break with newer versions of glibc.
+  #
+  # I also took out -Wextra because it spews out so much noise a serious problem was not noticed.
+  # It might go back in someday when I have more patience to clean up all the warnings.
+  #
   ###set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wvla -ffast-math -ftree-vectorize -D_XOPEN_SOURCE=600 -D_DEFAULT_SOURCE ${EXTRA_FLAGS}")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wvla -ffast-math -ftree-vectorize -D_XOPEN_SOURCE=600 -D_DEFAULT_SOURCE -D_BSD_SOURCE ${EXTRA_FLAGS}")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wvla -ffast-math -ftree-vectorize -D_GNU_SOURCE ${EXTRA_FLAGS}")
+  #
+  #
   # for math.h
   link_libraries("-lm")
 elseif (C_MSVC)

src/ax25_pad2.c

@@ -796,7 +796,7 @@ int main ()
 
 	  for (pf = 0; pf <= 1; pf++) {
 
- 	    int cmin, cmax;
+ 	    int cmin = 0, cmax = 1;
 
 	    switch (ftype) {
 					// 0 = response, 1 = command
@@ -867,7 +867,7 @@ int main ()
 
 /* SREJ is only S frame which can have information part. */
 
-	static char srej_info[] = { 1<<1, 2<<1, 3<<1, 4<<1 };
+	static unsigned char srej_info[] = { 1<<1, 2<<1, 3<<1, 4<<1 };
 
 	ftype = frame_type_S_SREJ;
 	for (pf = 0; pf <= 1; pf++) {