powerpc: Work around gcc miscompilation of __pa() on 64-bit (bdbc29c1) · Commits · 戴 / test

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: <stable@vger.kernel.org> Signed-off-by:

Paul Mackerras <paulus@samba.org> Signed-off-by:

Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -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"

arch/powerpc/include/asm/page.h

+10 −0

Original line number	Diff line number	Diff line
		@@ -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,

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