x64: explain where %rbp and %rbx are set

Signed-off-by: Elazar Leibovich <[email protected]> Signed-off-by: Pekka Enberg <[email protected]>
cloudius-systems · Jul 23, 2014 · 8fb28d3 · 8fb28d3
1 parent d72ab0d
commit 8fb28d3
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/arch/x64/boot.S b/arch/x64/boot.S
@@ -67,6 +67,7 @@ interrupt_stack_top = .
 
 .globl start32
 start32:
+    # boot16.S set %eax to ELF start address, we'll use it later
     mov %eax, %ebp
     lgdt gdt_desc
     mov $0x10, %eax
@@ -101,6 +102,7 @@ start64:
     xor %eax, %eax
     rep stosb
     mov %rbp, elf_header
+    # %ebx is set by boot16.S before running the loader
     mov %rbx, osv_multiboot_info
     lea init_stack_top, %rsp
     call premain