.section ".text.boot" // Make sure the linker puts this at the start of the kernel image
.global _start // Execution starts here
_start:
// Check processor ID is zero (executing on main core), else hang
mrs x1, mpidr_el1
and x1, x1, #3
cbz x1, 2f
// We're not on the main core, so hang in an infinite wait loop
1: wfe
b 1b
2: // We're on the main core!
// Set stack to start below our code
ldr x1, =_start
mov sp, x1
// Clean the BSS section
ldr x1, =__bss_start // Start address
ldr w2, =__bss_size // Size of the section
3: cbz w2, 4f // Quit loop if zero
str xzr, [x1], #8
sub w2, w2, #1
cbnz w2, 3b // Loop if non-zero
// Jump to our main() routine in C (make sure it doesn't return)
4: bl main
// In case it does return, halt the master core too
b 1b
I am looking some bare metal code for Raspberry PI 4B,this is a bootloader file named start.s. I don't konw the mean of
b 1b
what exactly is "1b"? It doesn's seem like the lable "1:". Is it a physical address?
I'm not a complete beginner in assembly, I just never came across this before. Please help me, if u konow the answer. Thanks.
I google it, but no answer.
