From bdbc29c19b2633b1d9c52638fb732bcde7a2031a Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Tue, 27 Aug 2013 16:07:49 +1000 Subject: [PATCH] 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 --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/page.h | 10 ++++++++++ 2 files changed, 11 insertions(+) diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index dbd9d3c..9cf59816d 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 kernel. +# This value must have zeroes in the bottom 60 bits otherwise lots will break config PAGE_OFFSET hex default "0xc000000000000000" diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h index 988c812..b9f4262 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) #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, -- 2.7.4