diff options
| -rw-r--r-- | tools/include/nolibc/nolibc.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h index 3430667b0d24..96b6d56acb57 100644 --- a/tools/include/nolibc/nolibc.h +++ b/tools/include/nolibc/nolibc.h @@ -399,14 +399,20 @@ struct stat { }) /* startup code */ +/* + * x86-64 System V ABI mandates: + * 1) %rsp must be 16-byte aligned right before the function call. + * 2) The deepest stack frame should be zero (the %rbp). + * + */ asm(".section .text\n" ".global _start\n" "_start:\n" "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) - "and $-16, %rsp\n" // x86 ABI : esp must be 16-byte aligned when - "sub $8, %rsp\n" // entering the callee + "xor %ebp, %ebp\n" // zero the stack frame + "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. "movzb %al, %rdi\n" // retrieve exit code from 8 lower bits "mov $60, %rax\n" // NR_exit == 60 |