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) : "" (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 : "" ((uintptr_t)(dest_buf) | (__funcp_address & 1))); \
78 \
79 __result; \
80 })
81
82 #endif /* !__ASM_FNCPY_H */
83
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