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From:   Zhangjin Wu <falcon@tinylab.org>
To:     thomas@t-8ch.de, w@1wt.eu
Cc:     falcon@tinylab.org, arnd@arndb.de, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org
Subject: [PATCH v1 08/11] tools/nolibc: mips: shrink _start with _start_c
Date:   Thu, 29 Jun 2023 03:01:14 +0800
Message-Id: <0d650309e0cf79fee1a87995d3fcae083b96b150.1687976753.git.falcon@tinylab.org>
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Let's move most of the _start operations to _start_c().

Also clean up the instructions in delay slots.

Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
---
 tools/include/nolibc/arch-mips.h | 45 +++++++-------------------------
 1 file changed, 9 insertions(+), 36 deletions(-)

diff --git a/tools/include/nolibc/arch-mips.h b/tools/include/nolibc/arch-mips.h
index ecf912a1938f..d0f73f03bfa1 100644
--- a/tools/include/nolibc/arch-mips.h
+++ b/tools/include/nolibc/arch-mips.h
@@ -173,50 +173,23 @@
 	_arg4 ? -_num : _num;							\
 })
 
-char **environ __attribute__((weak));
-const unsigned long *_auxv __attribute__((weak));
-
 /* startup code, note that it's called __start on MIPS */
 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __no_stack_protector __start(void)
 {
 	__asm__ volatile (
-		/*".set nomips16\n"*/
 		".set push\n"
-		".set    noreorder\n"
+		".set noreorder\n"
 		".option pic0\n"
 #ifdef _NOLIBC_STACKPROTECTOR
-		"jal __stack_chk_init\n" /* initialize stack protector                         */
-		"nop\n"                  /* delayed slot                                       */
+		"jal __stack_chk_init\n"	/* initialize stack protector			*/
+		" nop\n"			/* delayed slot					*/
 #endif
-		/*".ent __start\n"*/
-		/*"__start:\n"*/
-		"lw $a0,($sp)\n"        /* argc was in the stack                               */
-		"addiu  $a1, $sp, 4\n"  /* argv = sp + 4                                       */
-		"sll $a2, $a0, 2\n"     /* a2 = argc * 4                                       */
-		"add   $a2, $a2, $a1\n" /* envp = argv + 4*argc ...                            */
-		"addiu $a2, $a2, 4\n"   /*        ... + 4                                      */
-		"lui $a3, %hi(environ)\n"     /* load environ into a3 (hi)                     */
-		"addiu $a3, %lo(environ)\n"   /* load environ into a3 (lo)                     */
-		"sw $a2,($a3)\n"              /* store envp(a2) into environ                   */
-
-		"move $t0, $a2\n"             /* iterate t0 over envp, look for NULL           */
-		"0:"                          /* do {                                          */
-		"lw $a3, ($t0)\n"             /*   a3=*(t0);                                   */
-		"bne $a3, $0, 0b\n"           /* } while (a3);                                 */
-		"addiu $t0, $t0, 4\n"         /* delayed slot: t0+=4;                          */
-		"lui $a3, %hi(_auxv)\n"       /* load _auxv into a3 (hi)                       */
-		"addiu $a3, %lo(_auxv)\n"     /* load _auxv into a3 (lo)                       */
-		"sw $t0, ($a3)\n"             /* store t0 into _auxv                           */
-
-		"li $t0, -8\n"
-		"and $sp, $sp, $t0\n"   /* sp must be 8-byte aligned                           */
-		"addiu $sp,$sp,-16\n"   /* the callee expects to save a0..a3 there!            */
-		"jal main\n"            /* main() returns the status code, we'll exit with it. */
-		"nop\n"                 /* delayed slot                                        */
-		"move $a0, $v0\n"       /* retrieve 32-bit exit code from v0                   */
-		"li $v0, 4001\n"        /* NR_exit == 4001                                     */
-		"syscall\n"
-		/*".end __start\n"*/
+		"move  $a0, $sp\n"		/* save stack pointer to a0, as arg1 of _start_c*/
+		"li    $t0, -8\n"
+		"and   $sp, $sp, $t0\n"		/* sp must be 8-byte aligned			*/
+		"addiu $sp, $sp, -16\n"		/* the callee expects to save a0..a3 there	*/
+		"jal   _start_c\n"		/* transfer to c runtime			*/
+		" nop\n"			/* delayed slot					*/
 		".set pop\n"
 	);
 	__builtin_unreachable();
-- 
2.25.1