This is a note to let you know that I've just added the patch titled
powerpc: Work around gcc miscompilation of __pa() on 64-bit
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-work-around-gcc-miscompilation-of-__pa-on-64-bit.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From bdbc29c19b2633b1d9c52638fb732bcde7a2031a Mon Sep 17 00:00:00 2001
From: Paul Mackerras <paulus@xxxxxxxxx>
Date: Tue, 27 Aug 2013 16:07:49 +1000
Subject: powerpc: Work around gcc miscompilation of __pa() on 64-bit
From: Paul Mackerras <paulus@xxxxxxxxx>
commit bdbc29c19b2633b1d9c52638fb732bcde7a2031a upstream.
On 64-bit, __pa(&static_var) gets miscompiled by recent versions of
gcc as something like:
addis 3,2,.LANCHOR1+4611686018427387904@toc@ha
addi 3,3,.LANCHOR1+4611686018427387904@toc@l
This ends up effectively ignoring the offset, since its bottom 32 bits
are zero, and means that the result of __pa() still has 0xC in the top
nibble. This happens with gcc 4.8.1, at least.
To work around this, for 64-bit we make __pa() use an AND operator,
and for symmetry, we make __va() use an OR operator. Using an AND
operator rather than a subtraction ends up with slightly shorter code
since it can be done with a single clrldi instruction, whereas it
takes three instructions to form the constant (-PAGE_OFFSET) and add
it on. (Note that MEMORY_START is always 0 on 64-bit.)
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/page.h | 10 ++++++++++
2 files changed, 11 insertions(+)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -979,6 +979,7 @@ config RELOCATABLE
must live at a different physical address than the primary
kernel.
+# This value must have zeroes in the bottom 60 bits otherwise lots will break
config PAGE_OFFSET
hex
default "0xc000000000000000"
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -211,9 +211,19 @@ extern long long virt_phys_offset;
#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + VIRT_PHYS_OFFSET))
#define __pa(x) ((unsigned long)(x) - VIRT_PHYS_OFFSET)
#else
+#ifdef CONFIG_PPC64
+/*
+ * gcc miscompiles (unsigned long)(&static_var) - PAGE_OFFSET
+ * with -mcmodel=medium, so we use & and | instead of - and + on 64-bit.
+ */
+#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) | PAGE_OFFSET))
+#define __pa(x) ((unsigned long)(x) & 0x0fffffffffffffffUL)
+
+#else /* 32-bit, non book E */
#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + PAGE_OFFSET - MEMORY_START))
#define __pa(x) ((unsigned long)(x) - PAGE_OFFSET + MEMORY_START)
#endif
+#endif
/*
* Unfortunately the PLT is in the BSS in the PPC32 ELF ABI,
Patches currently in stable-queue which might be from paulus@xxxxxxxxx are
queue-3.4/powerpc-work-around-gcc-miscompilation-of-__pa-on-64-bit.patch
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