Due to the two-instruction sequence needed to access arbitrary memory
locations, the RISC-V linker aggressively optimises memory accesses and
jumps at link-time. This is called "linker relaxation," and is discussed
in this SiFive article
<https://www.sifive.com/blog/all-aboard-part-3-linker-relaxation-in-riscv-toolchain>.
One of the optimizations in place is to assume that the __global_pointer
symbol is placed in the gp register. To quote the article:
"...The magic __global_pointer$ symbol is defined to point 0x800 bytes
past the start of the .sdata section. The 0x800 magic number allows
signed 12-bit offsets from __global_pointer$ to address symbols at the
start of the .sdata section. The linker assumes that if this symbol is
defined, then the gp register contains that value, which it can then use
to relax accesses to global symbols within that 12-bit range. The
compiler treats the gp register as a constant so it doesn't need to be
saved or restored, which means it is generally only written by _start,
the ELF entry point."
However, U-Boot instead keeps the global data pointer in gp. This causes
memory accesses and jumps optimized to use the gp pointer to fail. To
fix this problem, we undefine the __global_pointer symbol.
Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
For RV64, it will use sd instruction to clear t0
register, and the increament will be 8 bytes. So
if the difference between__bss_strat and __bss_end
was not 8 bytes aligned, the clear bss loop will
overflow and acks like system hang.
Signed-off-by: Rick Chen <rick@andestech.com>
Cc: KC Lin <kclin@andestech.com>
Cc: Alan Kao <alankao@andestech.com>
Currently start.S is inside arch/riscv/cpu/ax25/, but it can be
common for all RISC-V targets.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
There are several coding style issues in the linker script. Fix them.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
The linker script can be shared by all RISC-V targets. Move it to
a common place.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
2018-10-03 17:47:31 +08:00
Renamed from arch/riscv/cpu/ax25/u-boot.lds (Browse further)
