5756e9dd0d
In low-level board support code, there is sometimes a need to copy a function body to another location at run-time. A straightforward call to memcpy doesn't work in Thumb-2, because bit 0 of external Thumb function symbols is set to 1, indicating that the function is Thumb. Without corrective measures, this will cause an off-by-one copy, and the copy may be called using the wrong instruction set. This patch adds an fncpy() macro to help with such copies. Particular care is needed, because C doesn't guarantee any defined behaviour when casting a function pointer to any other type. This has been observed to lead to strange optimisation side-effects when doing the arithmetic which is required in order to copy/move function bodies correctly in Thumb-2. Thanks to Russell King and Nicolas Pitre for their input on this patch. Signed-off-by: Dave Martin <dave.martin@linaro.org> Tested-by: Jean Pihet <j-pihet@ti.com> Tested-by: Tony Lindgren <tony@atomide.com> Tested-by: Kevin Hilman <khilman@ti.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
94 lines
3.1 KiB
C
94 lines
3.1 KiB
C
/*
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* arch/arm/include/asm/fncpy.h - helper macros for function body copying
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*
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* Copyright (C) 2011 Linaro Limited
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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/*
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* These macros are intended for use when there is a need to copy a low-level
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* function body into special memory.
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*
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* For example, when reconfiguring the SDRAM controller, the code doing the
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* reconfiguration may need to run from SRAM.
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*
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* NOTE: that the copied function body must be entirely self-contained and
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* position-independent in order for this to work properly.
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*
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* NOTE: in order for embedded literals and data to get referenced correctly,
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* the alignment of functions must be preserved when copying. To ensure this,
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* the source and destination addresses for fncpy() must be aligned to a
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* multiple of 8 bytes: you will be get a BUG() if this condition is not met.
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* You will typically need a ".align 3" directive in the assembler where the
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* function to be copied is defined, and ensure that your allocator for the
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* destination buffer returns 8-byte-aligned pointers.
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*
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* Typical usage example:
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*
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* extern int f(args);
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* extern uint32_t size_of_f;
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* int (*copied_f)(args);
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* void *sram_buffer;
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*
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* copied_f = fncpy(sram_buffer, &f, size_of_f);
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*
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* ... later, call the function: ...
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*
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* copied_f(args);
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*
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* The size of the function to be copied can't be determined from C:
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* this must be determined by other means, such as adding assmbler directives
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* in the file where f is defined.
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*/
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#ifndef __ASM_FNCPY_H
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#define __ASM_FNCPY_H
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#include <linux/types.h>
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#include <linux/string.h>
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#include <asm/bug.h>
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#include <asm/cacheflush.h>
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/*
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* Minimum alignment requirement for the source and destination addresses
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* for function copying.
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*/
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#define FNCPY_ALIGN 8
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#define fncpy(dest_buf, funcp, size) ({ \
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uintptr_t __funcp_address; \
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typeof(funcp) __result; \
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\
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asm("" : "=r" (__funcp_address) : "0" (funcp)); \
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\
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/* \
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* Ensure alignment of source and destination addresses, \
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* disregarding the function's Thumb bit: \
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*/ \
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BUG_ON((uintptr_t)(dest_buf) & (FNCPY_ALIGN - 1) || \
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(__funcp_address & ~(uintptr_t)1 & (FNCPY_ALIGN - 1))); \
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\
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memcpy(dest_buf, (void const *)(__funcp_address & ~1), size); \
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flush_icache_range((unsigned long)(dest_buf), \
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(unsigned long)(dest_buf) + (size)); \
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\
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asm("" : "=r" (__result) \
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: "0" ((uintptr_t)(dest_buf) | (__funcp_address & 1))); \
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\
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__result; \
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})
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#endif /* !__ASM_FNCPY_H */
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