The patch titled
compiler-gcc.h: add more comments to RELOC_HIDE
has been added to the -mm tree. Its filename is
compiler-gcch-add-more-comments-to-reloc_hide.patch
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------------------------------------------------------
Subject: compiler-gcc.h: add more comments to RELOC_HIDE
From: Andi Kleen <andi@xxxxxxxxxxxxxx>
Requested by C. Lameter
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Mike Travis <travis@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/compiler-gcc.h | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff -puN include/linux/compiler-gcc.h~compiler-gcch-add-more-comments-to-reloc_hide include/linux/compiler-gcc.h
--- a/include/linux/compiler-gcc.h~compiler-gcch-add-more-comments-to-reloc_hide
+++ a/include/linux/compiler-gcc.h
@@ -11,9 +11,19 @@
/* The "volatile" is due to gcc bugs */
#define barrier() __asm__ __volatile__("": : :"memory")
-/* This macro obfuscates arithmetic on a variable address so that gcc
- shouldn't recognize the original var, and make assumptions about it */
/*
+ * This macro obfuscates arithmetic on a variable address so that gcc
+ * shouldn't recognize the original var, and make assumptions about it.
+ *
+ * This is needed because the C standard makes it undefined to do
+ * pointer arithmetic on "objects" outside their boundaries and the
+ * gcc optimizers assume this is the case. In particular they
+ * assume such arithmetic does not wrap.
+ *
+ * A miscompilation has been observed because of this on PPC.
+ * To work around it we hide the relationship of the pointer and the object
+ * using this macro.
+ *
* Versions of the ppc64 compiler before 4.1 had a bug where use of
* RELOC_HIDE could trash r30. The bug can be worked around by changing
* the inline assembly constraint from =g to =r, in this particular
_
Patches currently in -mm which might be from andi@xxxxxxxxxxxxxx are
origin.patch
elf-implement-at_random-for-glibc-prng-seeding.patch
x86-only-scan-the-root-bus-in-early-pci-quirks.patch
x86-hpet-allow-force-enable-on-ich10-hpet.patch
mark-complex-bitopsh-inlines-as-__always_inline.patch
x86-avoid-theoretical-vmalloc-fault-loop.patch
compiler-gcch-add-more-comments-to-reloc_hide.patch
nilfs2-fix-problems-of-memory-allocation-in-ioctl.patch
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