https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78868
Bug ID: 78868
Summary: When one variadic function calls another one, the
parameters are reversed, if va_arg is used directly in
function call.
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: vlad at cloudflare dot com
Target Milestone: ---
Created attachment 40374
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40374&action=edit
Preprocessed source file
On Debian 8, when using gcc 4.9.2, when one variadic function calls another
one, the parameters are reversed, if va_arg is used directly in function call.
When va_arg is evaluated before the call into a temporary location, the order
is correct.
Also replicated in gcc 5.3.1.
Clang shows the expected behavior.
#include <stdarg.h>
int printf( const char* format, ... );
void vararg1(int n, ...) {
va_list args;
va_start(args, n);
printf("%d, %d\n", va_arg(args, int), va_arg(args, int));
va_end(args);
}
void vararg2(int n, ...) {
va_list args;
va_start(args, n);
int a = va_arg(args, int);
int b = va_arg(args, int);
printf("%d, %d\n", a, b);
va_end(args);
}
int main() {
vararg1(2, 12, 13);
vararg2(2, 12, 13);
return 0;
}
Gcc output:
13, 12
12, 13
Clang output:
12, 13
12, 13
