1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * arch/arm/include/asm/fncpy.h - helper macros for function body copying
4  *
5  * Copyright (C) 2011 Linaro Limited
6  */
7 
8 /*
9  * These macros are intended for use when there is a need to copy a low-level
10  * function body into special memory.
11  *
12  * For example, when reconfiguring the SDRAM controller, the code doing the
13  * reconfiguration may need to run from SRAM.
14  *
15  * NOTE: that the copied function body must be entirely self-contained and
16  * position-independent in order for this to work properly.
17  *
18  * NOTE: in order for embedded literals and data to get referenced correctly,
19  * the alignment of functions must be preserved when copying.  To ensure this,
20  * the source and destination addresses for fncpy() must be aligned to a
21  * multiple of 8 bytes: you will be get a BUG() if this condition is not met.
22  * You will typically need a ".align 3" directive in the assembler where the
23  * function to be copied is defined, and ensure that your allocator for the
24  * destination buffer returns 8-byte-aligned pointers.
25  *
26  * Typical usage example:
27  *
28  * extern int f(args);
29  * extern uint32_t size_of_f;
30  * int (*copied_f)(args);
31  * void *sram_buffer;
32  *
33  * copied_f = fncpy(sram_buffer, &f, size_of_f);
34  *
35  * ... later, call the function: ...
36  *
37  * copied_f(args);
38  *
39  * The size of the function to be copied can't be determined from C:
40  * this must be determined by other means, such as adding assmbler directives
41  * in the file where f is defined.
42  */
43 
44 #ifndef __ASM_FNCPY_H
45 #define __ASM_FNCPY_H
46 
47 #include <linux/types.h>
48 #include <linux/string.h>
49 
50 #include <asm/bug.h>
51 #include <asm/cacheflush.h>
52 
53 /*
54  * Minimum alignment requirement for the source and destination addresses
55  * for function copying.
56  */
57 #define FNCPY_ALIGN 8
58 
59 #define fncpy(dest_buf, funcp, size) ({					\
60 	uintptr_t __funcp_address;					\
61 	typeof(funcp) __result;						\
62 									\
63 	asm("" : "=r" (__funcp_address) : "0" (funcp));			\
64 									\
65 	/*								\
66 	 * Ensure alignment of source and destination addresses,	\
67 	 * disregarding the function's Thumb bit:			\
68 	 */								\
69 	BUG_ON((uintptr_t)(dest_buf) & (FNCPY_ALIGN - 1) ||		\
70 		(__funcp_address & ~(uintptr_t)1 & (FNCPY_ALIGN - 1)));	\
71 									\
72 	memcpy(dest_buf, (void const *)(__funcp_address & ~1), size);	\
73 	flush_icache_range((unsigned long)(dest_buf),			\
74 		(unsigned long)(dest_buf) + (size));			\
75 									\
76 	asm("" : "=r" (__result)					\
77 		: "0" ((uintptr_t)(dest_buf) | (__funcp_address & 1)));	\
78 									\
79 	__result;							\
80 })
81 
82 #endif /* !__ASM_FNCPY_H */
83