arch/riscv/include/asm/xip_fixup.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * XIP fixup macros, only useful in assembly.
   4  */
   5 #ifndef _ASM_RISCV_XIP_FIXUP_H
   6 #define _ASM_RISCV_XIP_FIXUP_H
   7
   8 #include <linux/pgtable.h>
   9
  10 #ifdef CONFIG_XIP_KERNEL
  11 .macro XIP_FIXUP_OFFSET reg
  12         /* Fix-up address in Flash into address in RAM early during boot before
  13          * MMU is up. Because generated code "thinks" data is in Flash, but it
  14          * is actually in RAM (actually data is also in Flash, but Flash is
  15          * read-only, thus we need to use the data residing in RAM).
  16          *
  17          * The start of data in Flash is _sdata and the start of data in RAM is
  18          * CONFIG_PHYS_RAM_BASE. So this fix-up essentially does this:
  19          * reg += CONFIG_PHYS_RAM_BASE - _start
  20          */
  21         li t0, CONFIG_PHYS_RAM_BASE
  22         add \reg, \reg, t0
  23         la t0, _sdata
  24         sub \reg, \reg, t0
  25 .endm
  26 .macro XIP_FIXUP_FLASH_OFFSET reg
  27         /* In linker script, at the transition from read-only section to
  28          * writable section, the VMA is increased while LMA remains the same.
  29          * (See in linker script how _sdata, __data_loc and LOAD_OFFSET is
  30          * changed)
  31          *
  32          * Consequently, early during boot before MMU is up, the generated code
  33          * reads the "writable" section at wrong addresses, because VMA is used
  34          * by compiler to generate code, but the data is located in Flash using
  35          * LMA.
  36          */
  37         la t0, _sdata
  38         sub \reg, \reg, t0
  39         la t0, __data_loc
  40         add \reg, \reg, t0
  41 .endm
  42 #else
  43 .macro XIP_FIXUP_OFFSET reg
  44 .endm
  45 .macro XIP_FIXUP_FLASH_OFFSET reg
  46 .endm
  47 #endif /* CONFIG_XIP_KERNEL */
  48
  49 #endif