buffer: Fix regression introduced by 6c7eaa and c306a6

Buffer (un)packing was broken on compilers that are not
gcc-compatible since the checks for an argument count of
-1 have been removed from ssh_buffer_(un)pack(). This
fix no longer uses GCC extensions for the __VA_NARG__
macro, but only plain C99.
Note: The macro can no longer count empty argument lists
(results in compile error) which was not needed anyway.

Signed-off-by: Tilo Eckert <tilo.eckert@flam.de>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

ConfigureChecks.cmake

@@ -379,18 +379,6 @@ int main(void)
     return 0;
 }" HAVE_GCC_VOLATILE_MEMORY_PROTECTION)
 
-check_c_source_compiles("
-#include <stdio.h>
-#define __VA_NARG__(...) (__VA_NARG_(_0, ## __VA_ARGS__, __RSEQ_N()) - 1)
-#define __VA_NARG_(...) __VA_ARG_N(__VA_ARGS__)
-#define __VA_ARG_N( _1, _2, _3, _4, _5, _6, _7, _8, _9,_10,N,...) N
-#define __RSEQ_N() 10, 9,  8,  7,  6,  5,  4,  3,  2,  1,  0
-#define myprintf(format, ...) printf((format), __VA_NARG__(__VA_ARGS__), __VA_ARGS__)
-int main(void) {
-    myprintf(\"%d %d %d %d\",1,2,3);
-    return 0;
-}" HAVE_GCC_NARG_MACRO)
-
 check_c_source_compiles("
 #include <stdio.h>
 int main(void) {

config.h.cmake

@@ -219,7 +219,6 @@
 #cmakedefine HAVE_DESTRUCTOR_ATTRIBUTE 1
 
 #cmakedefine HAVE_GCC_VOLATILE_MEMORY_PROTECTION 1
-#cmakedefine HAVE_GCC_NARG_MACRO 1
 
 #cmakedefine HAVE_COMPILER__FUNC__ 1
 #cmakedefine HAVE_COMPILER__FUNCTION__ 1

include/libssh/priv.h

@@ -328,7 +328,6 @@ void explicit_bzero(void *s, size_t n);
 /**
  * Get the argument cound of variadic arguments
  */
-#ifdef HAVE_GCC_NARG_MACRO
 /*
  * Since MSVC 2010 there is a bug in passing __VA_ARGS__ to subsequent
  * macros as a single token, which results in:
@@ -338,7 +337,7 @@ void explicit_bzero(void *s, size_t n);
 #define VA_APPLY_VARIADIC_MACRO(macro, tuple) macro tuple
 
 #define __VA_NARG__(...) \
-        (__VA_NARG_(_0, ## __VA_ARGS__, __RSEQ_N()) - 1)
+        (__VA_NARG_(__VA_ARGS__, __RSEQ_N()))
 #define __VA_NARG_(...) \
         VA_APPLY_VARIADIC_MACRO(__VA_ARG_N, (__VA_ARGS__))
 #define __VA_ARG_N( \
@@ -357,10 +356,6 @@ void explicit_bzero(void *s, size_t n);
         29, 28, 27, 26, 25, 24, 23, 22, 21, 20, \
         19, 18, 17, 16, 15, 14, 13, 12, 11, 10, \
          9,  8,  7,  6,  5,  4,  3,  2,  1,  0
-#else
-/* clang does not support the above construction */
-#define __VA_NARG__(...) (-1)
-#endif
 
 #define CLOSE_SOCKET(s) do { if ((s) != SSH_INVALID_SOCKET) { _XCLOSESOCKET(s); (s) = SSH_INVALID_SOCKET;} } while(0)
 

tests/unittests/torture_buffer.c

@@ -245,10 +245,8 @@ static void torture_buffer_pack_badformat(void **state){
 
     /* with additional format */
     rc = ssh_buffer_pack(buffer, "bb", b);
-#ifdef HAVE_GCC_NARG_MACRO
+    /* check that we detect the missing parameter */
-    /* We can only detect errors if we have support for NARG macros */
     assert_int_equal(rc, SSH_ERROR);
-#endif
 
     /* unpack with missing format */
     ssh_buffer_reinit(buffer);

tests/unittests/torture_threads_buffer.c

@@ -496,10 +496,8 @@ static void *thread_buffer_pack_badformat(void *threadid)
 
     /* with additional format */
     rc = ssh_buffer_pack(buffer, "bb", b);
-#ifdef HAVE_GCC_NARG_MACRO
+    /* check that we detect the missing parameter */
-    /* We can only detect errors if we have support for NARG macros */
     assert_int_equal(rc, SSH_ERROR);
-#endif
 
     /* unpack with missing format */
     ssh_buffer_reinit(buffer);