A user on an Opteron system I administer discovered a problem with vsprintf. The system is running the AMD64 version of Gentoo 2004.1 (with multilib support). C code to demonstrate the problem appears below. Correct output (produced for example on a P4 system running RedHat Enterprise Workstation w/GCC 3.2.3, or on Sun or SGI workstations running the vendors' commercial C compilers) is main. string: THIS IS A STRING len: 32, len1: 32 main. string: THIS IS A STRING while the 64 bit executable produced with GCC 3.3.3 on our Gentoo-powered Opteron system produces main. string: THIS IS A STRING len: 32, len1: 21 main. string: 4
A user on an Opteron system I administer discovered a problem with vsprintf. The system is running the AMD64 version of Gentoo 2004.1 (with multilib support). C code to demonstrate the problem appears below. Correct output (produced for example on a P4 system running RedHat Enterprise Workstation w/GCC 3.2.3, or on Sun or SGI workstations running the vendors' commercial C compilers) is main. string: THIS IS A STRING len: 32, len1: 32 main. string: THIS IS A STRING while the 64 bit executable produced with GCC 3.3.3 on our Gentoo-powered Opteron system produces main. string: THIS IS A STRING len: 32, len1: 21 main. string: 4öÿ¿ -- Al - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - /* Demonstrate vsprintf() problem. Dale Williamson June 2 2004 */ #include <stdio.h> #include <stdarg.h> char GOUT[4096]; int gprintf(char *format, ...); int main(int argc, char *argv[]) { return gprintf(" main. string: %s\n","THIS IS A STRING"); } int gprintf(char *format, ...) { int len,len1; va_list args; va_start(args,format); len=vfprintf(stdout,format,args); len1=vsprintf(GOUT,format,args); *(GOUT+len)='\0'; fprintf(stdout," len: %d, len1: %d\n",len,len1); fprintf(stdout,"%s",GOUT); va_end(args); return len; }
The problem also affects 64 bit versions of RedHat using GCC 3.2 and 3.4. Thus it appears to be a generic problem with the 64 bit version of glibc. -- Al
This is no bug, as you use the "args" twice without reinitialising them. It is clearly a bug to it like you do. len=vfprintf(stdout,format,args); +va_end(args) +va_start(format,args) len1=vsprintf(GOUT,format,args); is the proper implementation. Your code happens to work on x86, but it's clearly bogus to write C-Code like that, cause "args" is in an indefinite state after it is used.
sorry, s/va_start(format,args)/va_start(args,format)/
My bad! Thank you for the C programming lesson in any event. -- Al
