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authorZack Weinberg <zackw@panix.com>2017-06-08 15:39:03 -0400
committerZack Weinberg <zackw@panix.com>2017-06-08 15:39:03 -0400
commit5046dbb4a7eba5eccfd258f92f4735c9ffc8d069 (patch)
tree4470480d904b65cf14ca524f96f79eca818c3eaf /REORG.TODO/sysdeps/i386/start.S
parent199fc19d3aaaf57944ef036e15904febe877fc93 (diff)
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Prepare for radical source tree reorganization. zack/build-layout-experiment
All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).
Diffstat (limited to 'REORG.TODO/sysdeps/i386/start.S')
-rw-r--r--REORG.TODO/sysdeps/i386/start.S139
1 files changed, 139 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/i386/start.S b/REORG.TODO/sysdeps/i386/start.S
new file mode 100644
index 0000000000..ccb1e2b38f
--- /dev/null
+++ b/REORG.TODO/sysdeps/i386/start.S
@@ -0,0 +1,139 @@
+/* Startup code compliant to the ELF i386 ABI.
+   Copyright (C) 1995-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   In addition to the permissions in the GNU Lesser General Public
+   License, the Free Software Foundation gives you unlimited
+   permission to link the compiled version of this file with other
+   programs, and to distribute those programs without any restriction
+   coming from the use of this file. (The GNU Lesser General Public
+   License restrictions do apply in other respects; for example, they
+   cover modification of the file, and distribution when not linked
+   into another program.)
+
+   Note that people who make modified versions of this file are not
+   obligated to grant this special exception for their modified
+   versions; it is their choice whether to do so. The GNU Lesser
+   General Public License gives permission to release a modified
+   version without this exception; this exception also makes it
+   possible to release a modified version which carries forward this
+   exception.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This is the canonical entry point, usually the first thing in the text
+   segment.  The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
+   point runs, most registers' values are unspecified, except for:
+
+   %edx		Contains a function pointer to be registered with `atexit'.
+		This is how the dynamic linker arranges to have DT_FINI
+		functions called for shared libraries that have been loaded
+		before this code runs.
+
+   %esp		The stack contains the arguments and environment:
+		0(%esp)			argc
+		4(%esp)			argv[0]
+		...
+		(4*argc)(%esp)		NULL
+		(4*(argc+1))(%esp)	envp[0]
+		...
+					NULL
+*/
+
+	.text
+	.globl _start
+	.type _start,@function
+_start:
+	/* Clear the frame pointer.  The ABI suggests this be done, to mark
+	   the outermost frame obviously.  */
+	xorl %ebp, %ebp
+
+	/* Extract the arguments as encoded on the stack and set up
+	   the arguments for `main': argc, argv.  envp will be determined
+	   later in __libc_start_main.  */
+	popl %esi		/* Pop the argument count.  */
+	movl %esp, %ecx		/* argv starts just at the current stack top.*/
+
+	/* Before pushing the arguments align the stack to a 16-byte
+	(SSE needs 16-byte alignment) boundary to avoid penalties from
+	misaligned accesses.  Thanks to Edward Seidl <seidl@janed.com>
+	for pointing this out.  */
+	andl $0xfffffff0, %esp
+	pushl %eax		/* Push garbage because we allocate
+				   28 more bytes.  */
+
+	/* Provide the highest stack address to the user code (for stacks
+	   which grow downwards).  */
+	pushl %esp
+
+	pushl %edx		/* Push address of the shared library
+				   termination function.  */
+
+#ifdef SHARED
+	/* Load PIC register.  */
+	call 1f
+	addl $_GLOBAL_OFFSET_TABLE_, %ebx
+
+	/* Push address of our own entry points to .fini and .init.  */
+	leal __libc_csu_fini@GOTOFF(%ebx), %eax
+	pushl %eax
+	leal __libc_csu_init@GOTOFF(%ebx), %eax
+	pushl %eax
+
+	pushl %ecx		/* Push second argument: argv.  */
+	pushl %esi		/* Push first argument: argc.  */
+
+	pushl main@GOT(%ebx)
+
+	/* Call the user's main function, and exit with its value.
+	   But let the libc call main.    */
+	call __libc_start_main@PLT
+#else
+	/* Push address of our own entry points to .fini and .init.  */
+	pushl $__libc_csu_fini
+	pushl $__libc_csu_init
+
+	pushl %ecx		/* Push second argument: argv.  */
+	pushl %esi		/* Push first argument: argc.  */
+
+	pushl $main
+
+	/* Call the user's main function, and exit with its value.
+	   But let the libc call main.    */
+	call __libc_start_main
+#endif
+
+	hlt			/* Crash if somehow `exit' does return.  */
+
+#ifdef SHARED
+1:	movl	(%esp), %ebx
+	ret
+#endif
+
+/* To fulfill the System V/i386 ABI we need this symbol.  Yuck, it's so
+   meaningless since we don't support machines < 80386.  */
+	.section .rodata
+	.globl _fp_hw
+_fp_hw:	.long 3
+	.size _fp_hw, 4
+	.type _fp_hw,@object
+
+/* Define a symbol for the first piece of initialized data.  */
+	.data
+	.globl __data_start
+__data_start:
+	.long 0
+	.weak data_start
+	data_start = __data_start