linux-kernel - [PATCH v3 06/11] tools/nolibc: x86_64: shrink _start with _start

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Message-Id: <8bdc96799300a5c5a40320d4f66ad54e97b4b9de.1689150149.git.falcon@tinylab.org>
Date:   Wed, 12 Jul 2023 17:22:00 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     w@....eu
Cc:     falcon@...ylab.org, arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, thomas@...ch.de
Subject: [PATCH v3 06/11] tools/nolibc: x86_64: shrink _start with _start_c

move most of the _start operations to _start_c().

Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
---
 tools/include/nolibc/arch-x86_64.h | 28 +++++++---------------------
 1 file changed, 7 insertions(+), 21 deletions(-)

diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h
index e980ca5417d0..0048adf6b11f 100644
--- a/tools/include/nolibc/arch-x86_64.h
+++ b/tools/include/nolibc/arch-x86_64.h
@@ -8,6 +8,7 @@
 #define _NOLIBC_ARCH_X86_64_H
 
 #include "compiler.h"
+#include "crt.h"
 
 /* Syscalls for x86_64 :
  *   - registers are 64-bit
@@ -153,9 +154,6 @@
 	_ret;                                                                 \
 })
 
-char **environ __attribute__((weak));
-const unsigned long *_auxv __attribute__((weak));
-
 /* startup code */
 /*
  * x86-64 System V ABI mandates:
@@ -167,25 +165,13 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __no_stack_pr
 {
 	__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();
 }
-- 
2.25.1