[PATCH xrdb] predefined cpp macros can produce unexpected results (bug 3413)

[Matt Turner]

From: Matthieu Herrb <matthieu.herrb at laas.fr>

GNU cpp is predefining a number of symbols, depending on the host and target
architecture. This can produce some unexpected results: for example, the
expansion of CLIENTHOST if the host name is i386.my.domain.

The attached patch creates a new -undef option to xrdb that is passed to
cpp.
---
Should it be on by default?

Matthieu, please give your Signed-off-by.

 xrdb.c   |   12 +++++++++++-
 xrdb.man |    4 ++++
 2 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/xrdb.c b/xrdb.c
index 21005c0..68accf8 100644
--- a/xrdb.c
+++ b/xrdb.c
@@ -479,8 +479,11 @@ DoCmdDefines(String *buff)
 		*val = '=';
 	    } else
 		AddSimpleDef(buff, arg + 2);
-	} else
+	} else if (arg[1] == 'U') {
 	    AddUndef(buff, arg + 2);
+	} else if (!strcmp(arg, "-undef") && oper != OPSYMBOLS) {
+	    addstring(buff, " -undef");
+	}
     }
 }
 
@@ -867,6 +870,13 @@ main(int argc, char *argv[])
 		    fatal("%s: Too many -U/-D arguments\n", ProgramName);
 		}
 		continue;
+	    } else if (!strcmp ("-undef", arg)) {
+		if (num_cmd_defines < MAX_CMD_DEFINES) {
+		    cmd_defines[num_cmd_defines++] = "-undef";
+		} else {
+		    fatal("%s: Too many cpp arguments\n", ProgramName);
+		}
+		continue;
 	    }
 	    Syntax ();
 	} else if (arg[0] == '=') 
diff --git a/xrdb.man b/xrdb.man
index d0d45ad..ddf1a73 100644
--- a/xrdb.man
+++ b/xrdb.man
@@ -223,6 +223,10 @@ This option indicates that
 should not run the input file through a preprocessor before loading it
 into properties.
 .TP 8
+.B -undef
+This option is passed to the C preprocessor if used. It prevents it from
+predefining any system specific macros.
+.TP 8
 .B \-symbols
 This option indicates that the symbols that are defined for the preprocessor
 should be printed onto the standard output.
-- 
1.7.2.2