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[RFC PATCH mig 7/12] Drop -undef -ansi from cpp flags

From: Sergey Bugaev
Subject: [RFC PATCH mig 7/12] Drop -undef -ansi from cpp flags
Date: Sun, 12 Feb 2023 14:10:38 +0300

Since GNU Mach commit d30481122a5d24ad6b921062f93b9172ef922fc3,
i386/machine_types.defs defines types based on defined(__x86_64__).
Supressing the built-in macro definitions will now result in the wrong
type being silently selected.

-undef was initially introduced in commit
78b6a7665db7b2eae367e17102821cbdca231d19 without much of an explanation.
-ansi was introduced in commit 6940fb91859e46b2e96a331a029f2dc2a0ee51c9
"to avoid -Di386=1 and the like".

Since glibc has been using MIG with CPP set to a custom GCC invocation
which did *not* use either flag, it appears that everything works well
enough even without them. On the other hand, not having __x86_64__
defined most definetely causes issues for anything that does not set a
custom CPP when invoking MIG (i.e., most users). Other built-in
definitions could be used in the future in a similar way (e.g. on other
architectures); it's really more of a coincidence that they have not
been used until now, and things kept working with -undef.
 mig.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mig.in b/mig.in
index 63e0269..94fd500 100644
--- a/mig.in
+++ b/mig.in
@@ -38,7 +38,7 @@ migcom=${MIGDIR-$libexecdir}/${MIGCOM-@MIGCOM@}
 # The expansion of TARGET_CC might refer to ${CC}, so make sure it is defined.
-default_cpp="@TARGET_CC@ -E -x c -undef -ansi"
+default_cpp="@TARGET_CC@ -E -x c"

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