arch/arm/include/asm/fncpy.h

   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 */