[Support] Fix bug in llvm::sys::argumentsFitWithinSystemLimits() of Unix/Program.inc

[rafaelauler]

Summary

This patch fixes a subtle bug in the UNIX implementation of llvm::sys::argumentsFitWithinSystemLimits() regarding the misuse of a static variable. This bug causes our cached number that stores the system command line maximum length to be halved after each call to the function. With a sufficient number of calls to this function, it will eventually report any given command line string to be over system limits.

[• rafael]

LGTM.

[rafaelauler]

Thanks, could you please commit this?

[silvas]

Naming?

[rafaelauler]

Fixed naming.

[• rafael]

216415

lib/Support/Unix/Program.inc

 bool llvm::sys::argumentsFitWithinSystemLimits(ArrayRef<const char*> Args) {
   static long ArgMax = sysconf(_SC_ARG_MAX);
 
   // System says no practical limit.
   if (ArgMax == -1)
     return true;
 
   // Conservatively account for space required by environment variables.
-  ArgMax /= 2;
+  long HalfArgMax = ArgMax / 2;
 
   size_t ArgLength = 0;
   for (ArrayRef<const char*>::iterator I = Args.begin(), E = Args.end();
        I != E; ++I) {
     ArgLength += strlen(*I) + 1;
-    if (ArgLength > size_t(ArgMax)) {
+    if (ArgLength > size_t(HalfArgMax)) {
       return false;
     }
   }
   return true;
 }
 }