linux-kernel - [PATCH v1 05/11] tools/nolibc: aarch64: shrink _start with _start

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Date:   Thu, 29 Jun 2023 02:57:23 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     thomas@...ch.de, w@....eu
Cc:     falcon@...ylab.org, arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: [PATCH v1 05/11] tools/nolibc: aarch64: shrink _start with _start_c

Let's move most of the _start operations to _start_c().

Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
---
 tools/include/nolibc/arch-aarch64.h | 25 ++++---------------------
 1 file changed, 4 insertions(+), 21 deletions(-)

diff --git a/tools/include/nolibc/arch-aarch64.h b/tools/include/nolibc/arch-aarch64.h
index 4a8a6f386865..ef98a751783f 100644
--- a/tools/include/nolibc/arch-aarch64.h
+++ b/tools/include/nolibc/arch-aarch64.h
@@ -143,33 +143,16 @@
 	_arg1;									\
 })
 
-char **environ __attribute__((weak));
-const unsigned long *_auxv __attribute__((weak));
-
 /* startup code */
 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __no_stack_protector _start(void)
 {
 	__asm__ volatile (
 #ifdef _NOLIBC_STACKPROTECTOR
-		"bl __stack_chk_init\n"   /* initialize stack protector                     */
+		"bl __stack_chk_init\n"	/* initialize stack protector			*/
 #endif
-		"ldr x0, [sp]\n"     /* argc (x0) was in the stack                          */
-		"add x1, sp, 8\n"    /* argv (x1) = sp                                      */
-		"lsl x2, x0, 3\n"    /* envp (x2) = 8*argc ...                              */
-		"add x2, x2, 8\n"    /*           + 8 (skip null)                           */
-		"add x2, x2, x1\n"   /*           + argv                                    */
-		"adrp x3, environ\n"          /* x3 = &environ (high bits)                  */
-		"str x2, [x3, #:lo12:environ]\n" /* store envp into environ                 */
-		"mov x4, x2\n"       /* search for auxv (follows NULL after last env)       */
-		"0:\n"
-		"ldr x5, [x4], 8\n"  /* x5 = *x4; x4 += 8                                   */
-		"cbnz x5, 0b\n"      /* and stop at NULL after last env                     */
-		"adrp x3, _auxv\n"   /* x3 = &_auxv (high bits)                             */
-		"str x4, [x3, #:lo12:_auxv]\n" /* store x4 into _auxv                       */
-		"and sp, x1, -16\n"  /* sp must be 16-byte aligned in the callee            */
-		"bl main\n"          /* main() returns the status code, we'll exit with it. */
-		"mov x8, 93\n"       /* NR_exit == 93                                       */
-		"svc #0\n"
+		"mov x0, sp\n"		/* save stack pointer to x0, as arg1 of _start_c*/
+		"and sp, x0, -16\n"	/* sp must be 16-byte aligned in the callee	*/
+		"bl  _start_c\n"	/* transfer to c runtime			*/
 	);
 	__builtin_unreachable();
 }
-- 
2.25.1