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author | Dave Martin <dave.martin@linaro.org> | 2011-01-26 18:34:26 +0100 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2011-01-27 11:48:58 +0000 |
commit | 5756e9dd0de6d5c307773f8f734c0684b3098fdd (patch) | |
tree | 4a92eded1b93fd91d2c40bc5bb5cb0405daeed79 /arch/arm/include | |
parent | 6fb1b304255efc5c4c93874ac8c066272e257e28 (diff) | |
download | op-kernel-dev-5756e9dd0de6d5c307773f8f734c0684b3098fdd.zip op-kernel-dev-5756e9dd0de6d5c307773f8f734c0684b3098fdd.tar.gz |
ARM: 6640/1: Thumb-2: Symbol manipulation macros for function body copying
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>
Diffstat (limited to 'arch/arm/include')
-rw-r--r-- | arch/arm/include/asm/fncpy.h | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/arch/arm/include/asm/fncpy.h b/arch/arm/include/asm/fncpy.h new file mode 100644 index 0000000..de53547 --- /dev/null +++ b/arch/arm/include/asm/fncpy.h @@ -0,0 +1,94 @@ +/* + * 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 */ |