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ARM: 6640/1: Thumb-2: Symbol manipulation macros for function body copying

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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>
This commit is contained in:
Dave Martin 2011-01-26 18:34:26 +01:00 committed by Russell King
parent 6fb1b30425
commit 5756e9dd0d
1 changed files with 94 additions and 0 deletions
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arch/arm/include/asm/fncpy.h Normal file
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/*
* 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 */