Added a purpose comment for ioctl_fix_ctrl

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@27455 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 10 insertions, 0 deletions

diff --git a/gcc/fixinc/inclhack.def b/gcc/fixinc/inclhack.def
index bbdd401b27a..94517191e67 100644
--- a/gcc/fixinc/inclhack.def
+++ b/gcc/fixinc/inclhack.def
@@ -587,6 +587,16 @@ fix = {
 
 /*
  *  Fix CTRL macros
+ *
+ * Basically, what is supposed to be happening is that every
+ * _invocation_ of the "_CTRL()" or "CTRL()" macros is supposed to have
+ * its argument inserted into single quotes.  We _must_ do this because
+ * ANSI macro substitution rules prohibit looking inside quoted strings
+ * for the substitution names.  A side effect is that the quotes are
+ * inserted in the definitions of those macros as well.  So, the last
+ * three sed expressions are supposed to clean up the definitions, as
+ * long as those definitions are using "c", "g" or "x" as the macro
+ * argument :).  Yuck.
  */
 fix = {
     hackname = ioctl_fix_ctrl;