linux-kernel - [PATCH v2 12/12] tools/nolibc: s390/crt.h: shrink _start with _start

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Message-Id: <7246cc6042073168817a6fe36d8ff3c0c508e684.1688828139.git.falcon@tinylab.org>
Date:   Sat,  8 Jul 2023 23:38:48 +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 12/12] tools/nolibc: s390/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/s390/crt.h | 32 ++++----------------------------
 1 file changed, 4 insertions(+), 28 deletions(-)

diff --git a/tools/include/nolibc/s390/crt.h b/tools/include/nolibc/s390/crt.h
index 8580f615d525..e247b8a37475 100644
--- a/tools/include/nolibc/s390/crt.h
+++ b/tools/include/nolibc/s390/crt.h
@@ -10,34 +10,10 @@
 void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void)
 {
 	__asm__ volatile (
-		"lg	%r2,0(%r15)\n"		/* argument count */
-		"la	%r3,8(%r15)\n"		/* argument pointers */
-
-		"xgr	%r0,%r0\n"		/* r0 will be our NULL value */
-		/* search for envp */
-		"lgr	%r4,%r3\n"		/* start at argv */
-		"0:\n"
-		"clg	%r0,0(%r4)\n"		/* entry zero? */
-		"la	%r4,8(%r4)\n"		/* advance pointer */
-		"jnz	0b\n"			/* no -> test next pointer */
-						/* yes -> r4 now contains start of envp */
-		"larl	%r1,environ\n"
-		"stg	%r4,0(%r1)\n"
-
-		/* search for auxv */
-		"lgr	%r5,%r4\n"		/* start at envp */
-		"1:\n"
-		"clg	%r0,0(%r5)\n"		/* entry zero? */
-		"la	%r5,8(%r5)\n"		/* advance pointer */
-		"jnz	1b\n"			/* no -> test next pointer */
-		"larl	%r1,_auxv\n"		/* yes -> store value in _auxv */
-		"stg	%r5,0(%r1)\n"
-
-		"aghi	%r15,-160\n"		/* allocate new stackframe */
-		"xc	0(8,%r15),0(%r15)\n"	/* clear backchain */
-		"brasl	%r14,main\n"		/* ret value of main is arg to exit */
-		"lghi	%r1,1\n"		/* __NR_exit */
-		"svc	0\n"
+		"lgr	%r2, %r15\n"          /* save stack pointer to %r2, as arg1 of _start_c */
+		"aghi	%r15, -160\n"         /* allocate new stackframe                        */
+		"xc	0(8,%r15), 0(%r15)\n" /* clear backchain                                */
+		"brasl	%r14, _start_c\n"     /* transfer to c runtime                          */
 	);
 	__builtin_unreachable();
 }
-- 
2.25.1