path: root/arch/powerpc
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authorPaul Mackerras <paulus@samba.org>2013-08-27 16:07:49 +1000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-09-07 22:09:57 -0700
commit45fe50ea3dadb11c5094d71a4f3e3ccc6f41f1c5 (patch)
tree9571a807e628c9e9b6254c28b50e91eed1e4cd64 /arch/powerpc
parentc990ab45cb4fda0767b196f4303372bdad4f9f7a (diff)
powerpc: Work around gcc miscompilation of __pa() on 64-bit
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@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/powerpc')
2 files changed, 11 insertions, 0 deletions
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 74991fee2e6..fe404e77246 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -986,6 +986,7 @@ config RELOCATABLE
must live at a different physical address than the primary
+# This value must have zeroes in the bottom 60 bits otherwise lots will break
default "0xc000000000000000"
diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index 988c812aab5..b9f426212d3 100644
--- 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)
+#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)
* Unfortunately the PLT is in the BSS in the PPC32 ELF ABI,