linux-kernel - [PATCH v2 07/12] tools/nolibc: i386/crt.h: shrink _start with _start

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Message-Id: <1ca8535cdd8a6473c1bb6c8c7a8e4ff45e558ea3.1688828139.git.falcon@tinylab.org>
Date:   Sat,  8 Jul 2023 23:33:14 +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 v2 07/12] tools/nolibc: i386/crt.h: 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/i386/crt.h | 29 +++++++----------------------
 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/tools/include/nolibc/i386/crt.h b/tools/include/nolibc/i386/crt.h
index 0b88f7c887ae..87f31bc253a3 100644
--- a/tools/include/nolibc/i386/crt.h
+++ b/tools/include/nolibc/i386/crt.h
@@ -18,29 +18,14 @@ 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 %eax\n"                /* argc   (first arg, %eax)                      */
-		"mov %esp, %ebx\n"          /* argv[] (second arg, %ebx)                     */
-		"lea 4(%ebx,%eax,4),%ecx\n" /* then a NULL then envp (third arg, %ecx)       */
-		"mov %ecx, environ\n"       /* save environ                                  */
-		"xor %ebp, %ebp\n"          /* zero the stack frame                          */
-		"mov %ecx, %edx\n"          /* search for auxv (follows NULL after last env) */
-		"0:\n"
-		"add $4, %edx\n"            /* search for auxv using edx, it follows the     */
-		"cmp -4(%edx), %ebp\n"      /* ... NULL after last env (ebp is zero here)    */
-		"jnz 0b\n"
-		"mov %edx, _auxv\n"         /* save it into _auxv                            */
-		"and $-16, %esp\n"          /* x86 ABI : esp must be 16-byte aligned before  */
-		"sub $4, %esp\n"            /* the call instruction (args are aligned)       */
-		"push %ecx\n"               /* push all registers on the stack so that we    */
-		"push %ebx\n"               /* support both regparm and plain stack modes    */
-		"push %eax\n"
-		"call main\n"               /* main() returns the status code in %eax        */
-		"mov %eax, %ebx\n"          /* retrieve exit code (32-bit int)               */
-		"movl $1, %eax\n"           /* NR_exit == 1                                  */
-		"int $0x80\n"               /* exit now                                      */
-		"hlt\n"                     /* ensure it does not                            */
+		"xor  %ebp, %ebp\n"       /* zero the stack frame                                 */
+		"mov  %esp, %eax\n"       /* save stack pointer to %eax, as arg1 of _start_c      */
+		"and  $-16, %esp\n"       /* last pushed argument must be 16-byte aligned         */
+		"push %eax\n"             /* push arg1 on stack to support plain stack modes too  */
+		"call _start_c\n"         /* transfer to c runtime                                */
+		"hlt\n"                   /* ensure it does not return                            */
 	);
 	__builtin_unreachable();
 }
-- 
2.25.1