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1 /*
2  * arch/arm/include/asm/fncpy.h - helper macros for function body copying
3  *
4  * Copyright (C) 2011 Linaro Limited
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18  */
19 
20 /*
21  * These macros are intended for use when there is a need to copy a low-level
22  * function body into special memory.
23  *
24  * For example, when reconfiguring the SDRAM controller, the code doing the
25  * reconfiguration may need to run from SRAM.
26  *
27  * NOTE: that the copied function body must be entirely self-contained and
28  * position-independent in order for this to work properly.
29  *
30  * NOTE: in order for embedded literals and data to get referenced correctly,
31  * the alignment of functions must be preserved when copying.  To ensure this,
32  * the source and destination addresses for fncpy() must be aligned to a
33  * multiple of 8 bytes: you will be get a BUG() if this condition is not met.
34  * You will typically need a ".align 3" directive in the assembler where the
35  * function to be copied is defined, and ensure that your allocator for the
36  * destination buffer returns 8-byte-aligned pointers.
37  *
38  * Typical usage example:
39  *
40  * extern int f(args);
41  * extern uint32_t size_of_f;
42  * int (*copied_f)(args);
43  * void *sram_buffer;
44  *
45  * copied_f = fncpy(sram_buffer, &f, size_of_f);
46  *
47  * ... later, call the function: ...
48  *
49  * copied_f(args);
50  *
51  * The size of the function to be copied can't be determined from C:
52  * this must be determined by other means, such as adding assmbler directives
53  * in the file where f is defined.
54  */
55 
56 #ifndef __ASM_FNCPY_H
57 #define __ASM_FNCPY_H
58 
59 #include <linux/types.h>
60 #include <linux/string.h>
61 
62 #include <asm/bug.h>
63 #include <asm/cacheflush.h>
64 
65 /*
66  * Minimum alignment requirement for the source and destination addresses
67  * for function copying.
68  */
69 #define FNCPY_ALIGN 8
70 
71 #define fncpy(dest_buf, funcp, size) ({					\
72 	uintptr_t __funcp_address;					\
73 	typeof(funcp) __result;						\
74 									\
75 	asm("" : "=r" (__funcp_address) : "0" (funcp));			\
76 									\
77 	/*								\
78 	 * Ensure alignment of source and destination addresses,	\
79 	 * disregarding the function's Thumb bit:			\
80 	 */								\
81 	BUG_ON((uintptr_t)(dest_buf) & (FNCPY_ALIGN - 1) ||		\
82 		(__funcp_address & ~(uintptr_t)1 & (FNCPY_ALIGN - 1)));	\
83 									\
84 	memcpy(dest_buf, (void const *)(__funcp_address & ~1), size);	\
85 	flush_icache_range((unsigned long)(dest_buf),			\
86 		(unsigned long)(dest_buf) + (size));			\
87 									\
88 	asm("" : "=r" (__result)					\
89 		: "0" ((uintptr_t)(dest_buf) | (__funcp_address & 1)));	\
90 									\
91 	__result;							\
92 })
93 
94 #endif /* !__ASM_FNCPY_H */
95