Patrick Georgi (pgeorgi@google.com) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/12294
-gerrit
commit 3fa01f5b580765392ca019d14fadae1e53eaa413 Author: Patrick Georgi patrick@georgi-clan.de Date: Wed Jan 27 08:18:16 2016 +0100
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 --- src/include/stddef.h | 8 ++++++++ src/lib/program.ld | 4 ++++ 2 files changed, 12 insertions(+)
diff --git a/src/include/stddef.h b/src/include/stddef.h index b58f645..35326ed 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 865b5f6..9b8c7c9 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.*)