linux-kernel - [PATCH v3 10/11] tools/nolibc: s390: shrink _start with _start

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Message-Id: <fae6e54154d67e1dbec5f0ebc7958476a4ca1129.1689150149.git.falcon@tinylab.org>
Date:   Wed, 12 Jul 2023 17:26:21 +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 10/11] tools/nolibc: s390: 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-s390.h | 36 +++++---------------------------
 1 file changed, 5 insertions(+), 31 deletions(-)

diff --git a/tools/include/nolibc/arch-s390.h b/tools/include/nolibc/arch-s390.h
index a40424ba043e..051f3f4ed19b 100644
--- a/tools/include/nolibc/arch-s390.h
+++ b/tools/include/nolibc/arch-s390.h
@@ -9,6 +9,7 @@
 #include <asm/unistd.h>
 
 #include "compiler.h"
+#include "crt.h"
 
 /* Syscalls for s390:
  *   - registers are 64-bit
@@ -137,41 +138,14 @@
 	_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 (
-		"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