diff options
authorPaul Mackerras <>2013-08-27 16:07:49 +1000
committerBenjamin Herrenschmidt <>2013-08-27 16:59:30 +1000
commitbdbc29c19b2633b1d9c52638fb732bcde7a2031a (patch)
parentf5f6cbb61610b7bf9d9d96db9c3979d62a424bab (diff)
powerpc: Work around gcc miscompilation of __pa() on 64-bit
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.) CC: <> Signed-off-by: Paul Mackerras <> Signed-off-by: Benjamin Herrenschmidt <>
2 files changed, 11 insertions, 0 deletions
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index dbd9d3c991e8..9cf59816d3e9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -979,6 +979,7 @@ 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 988c812aab5b..b9f426212d3a 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,