[PATCH] FRV: Add FDPIC ELF binary format driver

The attached patch adds a new binary format driver that allows a special
variety of ELF to be used that permits the dynamic sections that comprise an
executable, its dynamic loader and its shared libaries and its stack and data
to be located anywhere within the address space.

This is used to provide shared libraries and shared executables (at least, as
far as the read-only dynamic sections go) on uClinux. Not only that, but the
same binaries can be run on MMU linux without a problem.

This is achieved by:

 (1) Passing loadmaps to the dynamic loader (or to a statically linked
     executable) to indicate the whereabouts of the various dynamic sections.

 (2) Using a GOT inside the program.

 (3) Passing setup_arg_pages() the stack pointer to be.

 (4) Allowing the arch greated control over how an executable is laid out in
     memory in MMU Linux.

 (5) Rewriting mm/nommu.c to support MAP_PRIVATE on files, thus allowing _mmap_
     to handle sharing of private-readonly mappings.
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/Kconfig.binfmt

@@ -23,6 +23,19 @@ config BINFMT_ELF
 	  ld.so (check the file <file:Documentation/Changes> for location and
 	  latest version).
 
+config BINFMT_ELF_FDPIC
+	bool "Kernel support for FDPIC ELF binaries"
+	default y
+	depends on FRV
+	help
+	  ELF FDPIC binaries are based on ELF, but allow the individual load
+	  segments of a binary to be located in memory independently of each
+	  other. This makes this format ideal for use in environments where no
+	  MMU is available as it still permits text segments to be shared,
+	  even if data segments are not.
+
+	  It is also possible to run FDPIC ELF binaries on MMU linux also.
+
 config BINFMT_FLAT
 	tristate "Kernel support for flat binaries"
 	depends on !MMU || SUPERH

fs/Makefile

@@ -25,6 +25,7 @@ obj-$(CONFIG_BINFMT_MISC)	+= binfmt_misc.o
 obj-y				+= binfmt_script.o
 
 obj-$(CONFIG_BINFMT_ELF)	+= binfmt_elf.o
+obj-$(CONFIG_BINFMT_ELF_FDPIC)	+= binfmt_elf_fdpic.o
 obj-$(CONFIG_BINFMT_SOM)	+= binfmt_som.o
 obj-$(CONFIG_BINFMT_FLAT)	+= binfmt_flat.o
 

include/linux/elf-fdpic.h

+/* elf-fdpic.h: FDPIC ELF load map
+ *
+ * Copyright (C) 2003 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#ifndef _LINUX_ELF_FDPIC_H
+#define _LINUX_ELF_FDPIC_H
+
+#include <linux/elf.h>
+
+#define PT_GNU_STACK    (PT_LOOS + 0x474e551)
+
+/* segment mappings for ELF FDPIC libraries/executables/interpreters */
+struct elf32_fdpic_loadseg {
+	Elf32_Addr	addr;		/* core address to which mapped */
+	Elf32_Addr	p_vaddr;	/* VMA recorded in file */
+	Elf32_Word	p_memsz;	/* allocation size recorded in file */
+};
+
+struct elf32_fdpic_loadmap {
+	Elf32_Half	version;	/* version of these structures, just in case... */
+	Elf32_Half	nsegs;		/* number of segments */
+	struct elf32_fdpic_loadseg segs[];
+};
+
+#define ELF32_FDPIC_LOADMAP_VERSION	0x0000
+
+/*
+ * binfmt binary parameters structure
+ */
+struct elf_fdpic_params {
+	struct elfhdr			hdr;		/* ref copy of ELF header */
+	struct elf_phdr			*phdrs;		/* ref copy of PT_PHDR table */
+	struct elf32_fdpic_loadmap	*loadmap;	/* loadmap to be passed to userspace */
+	unsigned long			elfhdr_addr;	/* mapped ELF header user address */
+	unsigned long			ph_addr;	/* mapped PT_PHDR user address */
+	unsigned long			map_addr;	/* mapped loadmap user address */
+	unsigned long			entry_addr;	/* mapped entry user address */
+	unsigned long			stack_size;	/* stack size requested (PT_GNU_STACK) */
+	unsigned long			dynamic_addr;	/* mapped PT_DYNAMIC user address */
+	unsigned long			load_addr;	/* user address at which to map binary */
+	unsigned long			flags;
+#define ELF_FDPIC_FLAG_ARRANGEMENT	0x0000000f	/* PT_LOAD arrangement flags */
+#define ELF_FDPIC_FLAG_INDEPENDENT	0x00000000	/* PT_LOADs can be put anywhere */
+#define ELF_FDPIC_FLAG_HONOURVADDR	0x00000001	/* PT_LOAD.vaddr must be honoured */
+#define ELF_FDPIC_FLAG_CONSTDISP	0x00000002	/* PT_LOADs require constant
+							 * displacement */
+#define ELF_FDPIC_FLAG_CONTIGUOUS	0x00000003	/* PT_LOADs should be contiguous */
+#define ELF_FDPIC_FLAG_EXEC_STACK	0x00000010	/* T if stack to be executable */
+#define ELF_FDPIC_FLAG_NOEXEC_STACK	0x00000020	/* T if stack not to be executable */
+#define ELF_FDPIC_FLAG_EXECUTABLE	0x00000040	/* T if this object is the executable */
+#define ELF_FDPIC_FLAG_PRESENT		0x80000000	/* T if this object is present */
+};
+
+#ifdef CONFIG_MMU
+extern void elf_fdpic_arch_lay_out_mm(struct elf_fdpic_params *exec_params,
+				      struct elf_fdpic_params *interp_params,
+				      unsigned long *start_stack,
+				      unsigned long *start_brk);
+#endif
+
+#endif /* _LINUX_ELF_FDPIC_H */

include/linux/personality.h

@@ -18,6 +18,9 @@ extern int		__set_personality(unsigned long);
  * These occupy the top three bytes.
  */
 enum {
+	FDPIC_FUNCPTRS =	0x0080000,	/* userspace function ptrs point to descriptors
+						 * (signal handling)
+						 */
 	MMAP_PAGE_ZERO =	0x0100000,
 	ADDR_COMPAT_LAYOUT =	0x0200000,
 	READ_IMPLIES_EXEC =	0x0400000,
@@ -43,6 +46,7 @@ enum {
 enum {
 	PER_LINUX =		0x0000,
 	PER_LINUX_32BIT =	0x0000 | ADDR_LIMIT_32BIT,
+	PER_LINUX_FDPIC =	0x0000 | FDPIC_FUNCPTRS,
 	PER_SVR4 =		0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO,
 	PER_SVR3 =		0x0002 | STICKY_TIMEOUTS | SHORT_INODE,
 	PER_SCOSVR3 =		0x0003 | STICKY_TIMEOUTS |