diff mbox series

[v2,4/8] riscv: drop the use of XIP_OFFSET in XIP_FIXUP_OFFSET

Message ID dba0409518b14ee83b346e099b1f7f934daf7b74.1717789719.git.namcao@linutronix.de (mailing list archive)
State Accepted
Commit e4eac34feda4959fad754004435512b24af73fe6
Headers show
Series remove size limit on XIP kernel | expand

Checks

Context Check Description
conchuod/vmtest-fixes-PR fail merge-conflict

Commit Message

Nam Cao June 7, 2024, 8:22 p.m. UTC 
XIP_OFFSET is the hard-coded offset of writable data section within the
kernel.

By hard-coding this value, the read-only section of the kernel (which is
placed before the writable data section) is restricted in size.

As a preparation to remove this hard-coded macro XIP_OFFSET entirely, stop
using XIP_OFFSET in XIP_FIXUP_OFFSET. Instead, use CONFIG_PHYS_RAM_BASE and
_sdata to do the same thing.

While at it, also add a description for XIP_FIXUP_OFFSET.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/include/asm/xip_fixup.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/arch/riscv/include/asm/xip_fixup.h b/arch/riscv/include/asm/xip_fixup.h
index b65bf6306f69..9ed2cfae09e0 100644
--- a/arch/riscv/include/asm/xip_fixup.h
+++ b/arch/riscv/include/asm/xip_fixup.h
@@ -9,8 +9,19 @@ 
 
 #ifdef CONFIG_XIP_KERNEL
 .macro XIP_FIXUP_OFFSET reg
-        REG_L t0, _xip_fixup
+	/* Fix-up address in Flash into address in RAM early during boot before
+	 * MMU is up. Because generated code "thinks" data is in Flash, but it
+	 * is actually in RAM (actually data is also in Flash, but Flash is
+	 * read-only, thus we need to use the data residing in RAM).
+	 *
+	 * The start of data in Flash is _sdata and the start of data in RAM is
+	 * CONFIG_PHYS_RAM_BASE. So this fix-up essentially does this:
+	 * reg += CONFIG_PHYS_RAM_BASE - _start
+	 */
+	li t0, CONFIG_PHYS_RAM_BASE
         add \reg, \reg, t0
+	la t0, _sdata
+	sub \reg, \reg, t0
 .endm
 .macro XIP_FIXUP_FLASH_OFFSET reg
 	la t0, __data_loc
@@ -19,7 +30,6 @@ 
 	add \reg, \reg, t0
 .endm
 
-_xip_fixup: .dword CONFIG_PHYS_RAM_BASE - CONFIG_XIP_PHYS_ADDR - XIP_OFFSET
 _xip_phys_offset: .dword CONFIG_XIP_PHYS_ADDR + XIP_OFFSET
 #else
 .macro XIP_FIXUP_OFFSET reg