[PATCH] [docs] Explain how to use multiple file-name patterns in RUNTESTFLAGS

[Daniel Santos]

OK, the problem is at line 4014 of gcc/Makefile.in:

          $(MAKE) TESTSUITEDIR="$(TESTSUITEDIR)"
RUNTESTFLAGS="$(RUNTESTFLAGS)" \
            check-parallel-$* \
 
Even worse, one can inject arbitrary shell commands here, not that I can
think of a scenario where it would be an actual security problem:

RUNTESTFLAGS="i386.exp=a b\"; beep\"" check-c

I presume that the solution would be to re-escape the contents of
RUNTESTFLAGS.

Daniel