linux-kernel - [PATCH v3 05/11] tools/nolibc: i386: shrink _start with _start

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Message-Id: <29e5222e81983e46c0dd8c043db66820ed80638b.1689150149.git.falcon@tinylab.org>
Date:   Wed, 12 Jul 2023 17:20:55 +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 05/11] tools/nolibc: i386: 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-i386.h | 33 ++++++++------------------------
 1 file changed, 8 insertions(+), 25 deletions(-)

diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h
index 1d4b683bc2cd..f0d0f5c364b8 100644
--- a/tools/include/nolibc/arch-i386.h
+++ b/tools/include/nolibc/arch-i386.h
@@ -8,6 +8,7 @@
 #define _NOLIBC_ARCH_I386_H
 
 #include "compiler.h"
+#include "crt.h"
 
 /* Syscalls for i386 :
  *   - mostly similar to x86_64
@@ -154,9 +155,6 @@
 	_eax;							\
 })
 
-char **environ __attribute__((weak));
-const unsigned long *_auxv __attribute__((weak));
-
 /* startup code */
 /*
  * i386 System V ABI mandates:
@@ -168,29 +166,14 @@ 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 %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