[PATCH v2 08/12] tools/nolibc: x86_64/crt.h: shrink _start with _start_c

[Zhangjin Wu]

move most of the _start operations to _start_c().

Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx>
---
 tools/include/nolibc/x86_64/crt.h | 25 +++++++------------------
 1 file changed, 7 insertions(+), 18 deletions(-)

diff --git a/tools/include/nolibc/x86_64/crt.h b/tools/include/nolibc/x86_64/crt.h
index 6fede1235efc..03899042854e 100644
--- a/tools/include/nolibc/x86_64/crt.h
+++ b/tools/include/nolibc/x86_64/crt.h
@@ -18,27 +18,16 @@ void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_
 {
 	__asm__ volatile (
 #ifdef _NOLIBC_STACKPROTECTOR
-		"call __stack_chk_init\n"   /* initialize stack protector                          */
+		"call __stack_chk_init\n" /* initialize stack protector                      */
 #endif
-		"pop %rdi\n"                /* argc   (first arg, %rdi)                            */
-		"mov %rsp, %rsi\n"          /* argv[] (second arg, %rsi)                           */
-		"lea 8(%rsi,%rdi,8),%rdx\n" /* then a NULL then envp (third arg, %rdx)             */
-		"mov %rdx, environ\n"       /* save environ                                        */
-		"xor %ebp, %ebp\n"          /* zero the stack frame                                */
-		"mov %rdx, %rax\n"          /* search for auxv (follows NULL after last env)       */
-		"0:\n"
-		"add $8, %rax\n"            /* search for auxv using rax, it follows the           */
-		"cmp -8(%rax), %rbp\n"      /* ... NULL after last env (rbp is zero here)          */
-		"jnz 0b\n"
-		"mov %rax, _auxv\n"         /* save it into _auxv                                  */
-		"and $-16, %rsp\n"          /* x86 ABI : esp must be 16-byte aligned before call   */
-		"call main\n"               /* main() returns the status code, we'll exit with it. */
-		"mov %eax, %edi\n"          /* retrieve exit code (32 bit)                         */
-		"mov $60, %eax\n"           /* NR_exit == 60                                       */
-		"syscall\n"                 /* really exit                                         */
-		"hlt\n"                     /* ensure it does not return                           */
+		"xor  %ebp, %ebp\n"       /* zero the stack frame                            */
+		"mov  %rsp, %rdi\n"       /* save stack pointer to %rdi, as arg1 of _start_c */
+		"and  $-16, %rsp\n"       /* %rsp must be 16-byte aligned before call        */
+		"call _start_c\n"         /* transfer to c runtime                           */
+		"hlt\n"                   /* ensure it does not return                       */
 	);
 	__builtin_unreachable();
+
 }
 
 #endif /* _NOLIBC_X86_64_CRT_H */
-- 
2.25.1