From ff8076d75ace8da247b927f7de37f3ed5081b55e Mon Sep 17 00:00:00 2001
From: Patrick Georgi <patrick@georgi-clan.de>
Date: Wed, 27 Jan 2016 08:18:16 +0100
Subject: Provide a gcc-safe zero pointer
zeroptr is a linker object pointing at 0 that can be used to thwart
GCC's (and other compilers') "dereferencing NULL is undefined"
optimization strategy when it gets in the way.
Change-Id: I6aa6f28283281ebae73d6349811e290bf1b99483
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: https://review.coreboot.org/12294
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
---
src/include/stddef.h | 8 ++++++++
src/lib/program.ld | 4 ++++
2 files changed, 12 insertions(+)
(limited to 'src')
diff --git a/src/include/stddef.h b/src/include/stddef.h
index b58f645a3b..35326ed6c6 100644
--- a/src/include/stddef.h
+++ b/src/include/stddef.h
@@ -34,4 +34,12 @@ typedef unsigned int wint_t;
#define MAYBE_STATIC static
#endif
+#ifndef __ROMCC__
+/* Provide a pointer to address 0 that thwarts any "accessing this is
+ * undefined behaviour and do whatever" trickery in compilers.
+ * Use when you _really_ need to read32(zeroptr) (ie. read address 0).
+ */
+extern void *zeroptr;
+#endif
+
#endif /* STDDEF_H */
diff --git a/src/lib/program.ld b/src/lib/program.ld
index 865b5f6aa7..9b8c7c9ec1 100644
--- a/src/lib/program.ld
+++ b/src/lib/program.ld
@@ -133,6 +133,10 @@ _eprogram = .;
/* Discard the sections we don't need/want */
+.zeroptr 0 (NOLOAD) : {
+ zeroptr = .;
+}
+
/DISCARD/ : {
*(.comment)
*(.comment.*)
--
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