After more patches code for jumping to _start_cont symbol in flash memory
involved to code with useless mathematical operations. Currently it does:
r3 := CONFIG_SYS_MONITOR_BASE + ABS(_start_cont) - CONFIG_SYS_MONITOR_BASE
jump to r3
Which is equivalent of just:
r3 := ABS(_start_cont)
jump to r3
The purpose of that code is just to jump to _start_code symbol,
independently of program counter. So branch must be done to absolute
address. Trying to write:
ba _start_cont
just cause linker error:
LD u-boot
powerpc-linux-gnuspe-ld.bfd: arch/powerpc/cpu/mpc85xx/start.o: in function
`switch_as':
(.bootpg+0x4b8): relocation truncated to fit: R_PPC_ADDR24 against symbol
`_start_cont' defined in .text section in arch/powerpc/cpu/mpc85xx/start.o
make: *** [Makefile:1801: u-boot] Error 1
Probably by the fact that absolute address cannot be expressed by 24-bits.
So write the code via mtlr+blr pattern as it was before and load general
purpose register with absolute address of the symbol:
lis r3,_start_cont@h
ori r3,r3,_start_cont@l
mtlr r3
blr
Seems that gcc and gnu ld linker support symbol@h and symbol@l syntax like
number@h and number@l without any problem. And disassembling of compiler
u-boot binary proved that lis+ori instructions are called with numbers
which represent halves of absolute address of _start_cont symbol.
Signed-off-by: Pali Rohár <p...@kernel.org>
---
arch/powerpc/cpu/mpc85xx/start.S | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/cpu/mpc85xx/start.S b/arch/powerpc/cpu/mpc85xx/start.S
index 50b23a97662c..6e3900e7923b 100644
--- a/arch/powerpc/cpu/mpc85xx/start.S
+++ b/arch/powerpc/cpu/mpc85xx/start.S
@@ -1211,9 +1211,8 @@ switch_as:
#else
/* Calculate absolute address in FLASH and jump there */
/*--------------------------------------------------------------*/
- lis r3,CONFIG_SYS_MONITOR_BASE@h
- ori r3,r3,CONFIG_SYS_MONITOR_BASE@l
- addi r3,r3,_start_cont - CONFIG_SYS_MONITOR_BASE
+ lis r3,_start_cont@h
+ ori r3,r3,_start_cont@l
mtlr r3
blr
#endif
--
2.20.1
