mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-09-04 20:19:47 +08:00
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>
95 lines
3.1 KiB
C
95 lines
3.1 KiB
C
/*
|
|
* arch/arm/include/asm/fncpy.h - helper macros for function body copying
|
|
*
|
|
* Copyright (C) 2011 Linaro Limited
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License version 2 as
|
|
* published by the Free Software Foundation.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, write to the Free Software
|
|
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
|
|
*/
|
|
|
|
/*
|
|
* These macros are intended for use when there is a need to copy a low-level
|
|
* function body into special memory.
|
|
*
|
|
* For example, when reconfiguring the SDRAM controller, the code doing the
|
|
* reconfiguration may need to run from SRAM.
|
|
*
|
|
* NOTE: that the copied function body must be entirely self-contained and
|
|
* position-independent in order for this to work properly.
|
|
*
|
|
* NOTE: in order for embedded literals and data to get referenced correctly,
|
|
* the alignment of functions must be preserved when copying. To ensure this,
|
|
* the source and destination addresses for fncpy() must be aligned to a
|
|
* multiple of 8 bytes: you will be get a BUG() if this condition is not met.
|
|
* You will typically need a ".align 3" directive in the assembler where the
|
|
* function to be copied is defined, and ensure that your allocator for the
|
|
* destination buffer returns 8-byte-aligned pointers.
|
|
*
|
|
* Typical usage example:
|
|
*
|
|
* extern int f(args);
|
|
* extern uint32_t size_of_f;
|
|
* int (*copied_f)(args);
|
|
* void *sram_buffer;
|
|
*
|
|
* copied_f = fncpy(sram_buffer, &f, size_of_f);
|
|
*
|
|
* ... later, call the function: ...
|
|
*
|
|
* copied_f(args);
|
|
*
|
|
* The size of the function to be copied can't be determined from C:
|
|
* this must be determined by other means, such as adding assmbler directives
|
|
* in the file where f is defined.
|
|
*/
|
|
|
|
#ifndef __ASM_FNCPY_H
|
|
#define __ASM_FNCPY_H
|
|
|
|
#include <linux/types.h>
|
|
#include <linux/string.h>
|
|
|
|
#include <asm/bug.h>
|
|
#include <asm/cacheflush.h>
|
|
|
|
/*
|
|
* Minimum alignment requirement for the source and destination addresses
|
|
* for function copying.
|
|
*/
|
|
#define FNCPY_ALIGN 8
|
|
|
|
#define fncpy(dest_buf, funcp, size) ({ \
|
|
uintptr_t __funcp_address; \
|
|
typeof(funcp) __result; \
|
|
\
|
|
asm("" : "=r" (__funcp_address) : "0" (funcp)); \
|
|
\
|
|
/* \
|
|
* Ensure alignment of source and destination addresses, \
|
|
* disregarding the function's Thumb bit: \
|
|
*/ \
|
|
BUG_ON((uintptr_t)(dest_buf) & (FNCPY_ALIGN - 1) || \
|
|
(__funcp_address & ~(uintptr_t)1 & (FNCPY_ALIGN - 1))); \
|
|
\
|
|
memcpy(dest_buf, (void const *)(__funcp_address & ~1), size); \
|
|
flush_icache_range((unsigned long)(dest_buf), \
|
|
(unsigned long)(dest_buf) + (size)); \
|
|
\
|
|
asm("" : "=r" (__result) \
|
|
: "0" ((uintptr_t)(dest_buf) | (__funcp_address & 1))); \
|
|
\
|
|
__result; \
|
|
})
|
|
|
|
#endif /* !__ASM_FNCPY_H */
|