[PATCH] i386 vsyscall DSO implementation

[Roland McGrath <roland@redhat.com>]

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[Please remember that I am not on the mailing list, so make sure any
replies are also addressed to me directly.]

This patch against 2.5.68 turns the i386 vsyscall page into an ELF DSO, as
we discussed earlier.  I usurped the AT_SYSINFO_EH_FRAME number and
replaced it with AT_SYSINFO_EHDR, which points at the beginning of the page
where the DSO's ELF header is found.  Though AT_SYSINFO is left in for
compatibility, it is now superfluous since the vsyscall entry point can be
got from the e_entry field via AT_SYSINFO_EHDR with no additional overhead.

Two DSOs are built (a int $0x80 one and a sysenter one), using normal
assembly code and ld -shared with a special linker script.  Both images
(stripped ELF .so files) are embedded in __initdata space; sysenter_setup
copies one or the other whole image into the vsyscall page.  Each image is
a little under 2k (1884 and 1924) now, and could be trimmed a little bit
with some specialized ELF stripping that ld and strip don't do.  Adding
additional entry points should not have much additional overhead beyond the
code itself and the string size of new symbol names.

The code in the page is identical and still packed the same, but now at
0xffffe400.  The initializers for the page's contents are replaced with
assembly written like normal user-mode code, which is much easier to
maintain.  (Special care must still be taken by hand to make sure that the
entry points in both DSOs match up.)  Using a little additional ld
trickery, hand-written address constants for locations in the vsyscall page
are replaced with symbols that resolve the same at link-time but never need
hand-tweaking to match future changes to the vsyscall page code.  The
address 0xffffe000 is hard-wired in one place in the linker script used to
create the DSOs, and only there.

This patch also changes i386 core dumps to include the vsyscall DSO image
in the dump.  I believe this is important to do so that port-mortem
analysis of a core dump from a process that might have used PCs in the
vsyscall page does not depend on having the live kernel and hardware at the
time of analysis match the vsyscall page contents of the kernel that wrote
the core dump.  As well as dumping the memory, it copies other phdrs from
the DSO into the core file.  This is important to get the PT_GNU_EH_FRAME
information into the dump, where it serves the same purpose for post-mortem
analysis by the debugger that it serves in the live vsyscall DSO image for
cancelation handling.

I have tested the vsyscall DSO image with libc changes that use it (as well
as existing libc that needs AT_SYSINFO to work as it has before).
I have tested that core dumps are valid ELF and the new segments look correct.

Nothing yet in use needs the DSO to have symbol names, or an ELF soname, or
ELF symbol versions.  The selection of soname (in Makefile) and symbol
versions (in vsyscall.lds) are arbitrary and shouldn't be considered final
without some more thought.  Those can be changed or removed without
affecting anything in the kernel.  The exported symbol names __kernel_* are
also used inside the kernel now, but labels can be made in vsyscall-*.S for
kernel use irrespective of what names are chosen to export in the DSO
symbol table.

Please let me know if you like this or don't.


Thanks,
Roland



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--- stock-2.5.68/arch/i386/kernel/Makefile	Sat Apr 19 19:48:53 2003
+++ linux-2.5.68/arch/i386/kernel/Makefile	Wed Apr 23 21:03:25 2003
@@ -27,9 +27,29 @@ obj-$(CONFIG_SOFTWARE_SUSPEND)	+= suspen
 obj-$(CONFIG_X86_NUMAQ)		+= numaq.o
 obj-$(CONFIG_EDD)             	+= edd.o
 obj-$(CONFIG_MODULES)		+= module.o
-obj-y				+= sysenter.o
+obj-y				+= sysenter.o vsyscall.o
 obj-$(CONFIG_ACPI_SRAT) 	+= srat.o
 
 EXTRA_AFLAGS   := -traditional
 
 obj-$(CONFIG_SCx200)		+= scx200.o
+
+# vsyscall.o contains the vsyscall DSO images as __initdata.
+# We must build both images before we can assemble it.
+$(obj)/vsyscall.o: $(obj)/vsyscall-int80.so $(obj)/vsyscall-sysenter.so
+extra-y += $(foreach F,int80 sysenter,vsyscall-$F.o vsyscall-$F.so)
+
+# The DSO images are built using a special linker script.
+$(obj)/vsyscall-int80.so $(obj)/vsyscall-sysenter.so: \
+$(obj)/vsyscall-%.so: $(src)/vsyscall.lds $(obj)/vsyscall-%.o
+	$(CC) -nostdlib -shared -s -Wl,-soname=linux-vsyscall.so.1 \
+	      -o $@ -Wl,-T,$^
+
+# We also create a special relocatable object that should mirror the symbol
+# table and layout of the linked DSO.  With ld -R we can then refer to
+# these symbols in the kernel code rather than hand-coded addresses.
+extra-y += vsyscall-syms.o
+$(obj)/built-in.o: $(obj)/vsyscall-syms.o
+$(obj)/built-in.o: ld_flags += -R $(obj)/vsyscall-syms.o
+$(obj)/vsyscall-syms.o: $(src)/vsyscall.lds $(obj)/vsyscall-sysenter.o
+	$(CC) -nostdlib -r -o $@ -Wl,-T,$^
--- stock-2.5.68/arch/i386/kernel/entry.S	Sat Apr 19 19:48:56 2003
+++ linux-2.5.68/arch/i386/kernel/entry.S	Wed Apr 23 20:37:55 2003
@@ -230,8 +230,8 @@ need_resched:
 	jmp need_resched
 #endif
 
-/* Points to after the "sysenter" instruction in the vsyscall page */
-#define SYSENTER_RETURN 0xffffe010
+/* SYSENTER_RETURN points to after the "sysenter" instruction in
+   the vsyscall page.  See vsyscall-sysentry.S, which defines the symbol.  */
 
 	# sysenter call handler stub
 ENTRY(sysenter_entry)
--- stock-2.5.68/arch/i386/kernel/signal.c	Sat Apr 19 19:49:25 2003
+++ linux-2.5.68/arch/i386/kernel/signal.c	Wed Apr 23 20:35:43 2003
@@ -19,6 +19,7 @@
 #include <linux/stddef.h>
 #include <linux/personality.h>
 #include <linux/suspend.h>
+#include <linux/elf.h>
 #include <asm/ucontext.h>
 #include <asm/uaccess.h>
 #include <asm/i387.h>
@@ -347,6 +348,10 @@ get_sigframe(struct k_sigaction *ka, str
 	return (void __user *)((esp - frame_size) & -8ul);
 }
 
+/* These symbols are defined with the addresses in the vsyscall page.
+   See vsyscall-sigreturn.S.  */
+extern void __kernel_sigreturn, __kernel_rt_sigreturn;
+
 static void setup_frame(int sig, struct k_sigaction *ka,
 			sigset_t *set, struct pt_regs * regs)
 {
@@ -379,7 +384,7 @@ static void setup_frame(int sig, struct 
 	if (err)
 		goto give_sigsegv;
 
-	restorer = (void *) (fix_to_virt(FIX_VSYSCALL) + 32);
+	restorer = &__kernel_sigreturn;
 	if (ka->sa.sa_flags & SA_RESTORER)
 		restorer = ka->sa.sa_restorer;
 
@@ -462,7 +467,7 @@ static void setup_rt_frame(int sig, stru
 		goto give_sigsegv;
 
 	/* Set up to return from userspace.  */
-	restorer = (void *) (fix_to_virt(FIX_VSYSCALL) + 64);
+	restorer = &__kernel_rt_sigreturn;
 	if (ka->sa.sa_flags & SA_RESTORER)
 		restorer = ka->sa.sa_restorer;
 	err |= __put_user(restorer, &frame->pretcode);
--- stock-2.5.68/arch/i386/kernel/sysenter.c	Sat Apr 19 19:51:16 2003
+++ linux-2.5.68/arch/i386/kernel/sysenter.c	Wed Apr 23 02:16:02 2003
@@ -51,151 +51,30 @@ void enable_sep_cpu(void *info)
 	put_cpu();	
 }
 
+/*
+ * These symbols are defined by vsyscall.o to mark the bounds
+ * of the ELF DSO images included therein.
+ */
+extern const char vsyscall_int80_start, vsyscall_int80_end;
+extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
+
 static int __init sysenter_setup(void)
 {
-	static const char __initdata int80[] = {
-		0xcd, 0x80,		/* int $0x80 */
-		0xc3			/* ret */
-	};
-	/* Unwind information for the int80 code.  Keep track of
-	   where the return address is stored.  */
-	static const char __initdata int80_eh_frame[] = {
-	/* First the Common Information Entry (CIE):  */
-		0x14, 0x00, 0x00, 0x00,	/* Length of the CIE */
-		0x00, 0x00, 0x00, 0x00,	/* CIE Identifier Tag */
-		0x01,			/* CIE Version */
-		'z', 'R', 0x00,		/* CIE Augmentation */
-		0x01,			/* CIE Code Alignment Factor */
-		0x7c,			/* CIE Data Alignment Factor */
-		0x08,			/* CIE RA Column */
-		0x01,			/* Augmentation size */
-		0x1b,			/* FDE Encoding (pcrel sdata4) */
-		0x0c,			/* DW_CFA_def_cfa */
-		0x04,
-		0x04,
-		0x88,			/* DW_CFA_offset, column 0x8 */
-		0x01,
-		0x00,			/* padding */
-		0x00,
-	/* Now the FDE which contains the instructions for the frame.  */
-		0x0a, 0x00, 0x00, 0x00,	/* FDE Length */
-		0x1c, 0x00, 0x00, 0x00,	/* FDE CIE offset */
-	/* The PC-relative offset to the beginning of the code this
-	   FDE covers.  The computation below assumes that the offset
-	   can be represented in one byte.  Change if this is not true
-	   anymore.  The offset from the beginning of the .eh_frame
-	   is represented by EH_FRAME_OFFSET.  The word with the offset
-	   starts at byte 0x20 of the .eh_frame.  */
-		0x100 - (EH_FRAME_OFFSET + 0x20),
-		0xff, 0xff, 0xff,	/* FDE initial location */
-		3,			/* FDE address range */
-		0x00			/* Augmentation size */
-	/* The code does not change the stack pointer.  We need not
-	   record any operations.  */
-	};
-	static const char __initdata sysent[] = {
-		0x51,			/* push %ecx */
-		0x52,			/* push %edx */
-		0x55,			/* push %ebp */
-	/* 3: backjump target */
-		0x89, 0xe5,		/* movl %esp,%ebp */
-		0x0f, 0x34,		/* sysenter */
-
-	/* 7: align return point with nop's to make disassembly easier */
-		0x90, 0x90, 0x90, 0x90,
-		0x90, 0x90, 0x90,
-
-	/* 14: System call restart point is here! (SYSENTER_RETURN - 2) */
-		0xeb, 0xf3,		/* jmp to "movl %esp,%ebp" */
-	/* 16: System call normal return point is here! (SYSENTER_RETURN in entry.S) */
-		0x5d,			/* pop %ebp */
-		0x5a,			/* pop %edx */
-		0x59,			/* pop %ecx */
-		0xc3			/* ret */
-	};
-	/* Unwind information for the sysenter code.  Keep track of
-	   where the return address is stored.  */
-	static const char __initdata sysent_eh_frame[] = {
-	/* First the Common Information Entry (CIE):  */
-		0x14, 0x00, 0x00, 0x00,	/* Length of the CIE */
-		0x00, 0x00, 0x00, 0x00,	/* CIE Identifier Tag */
-		0x01,			/* CIE Version */
-		'z', 'R', 0x00,		/* CIE Augmentation */
-		0x01,			/* CIE Code Alignment Factor */
-		0x7c,			/* CIE Data Alignment Factor */
-		0x08,			/* CIE RA Column */
-		0x01,			/* Augmentation size */
-		0x1b,			/* FDE Encoding (pcrel sdata4) */
-		0x0c,			/* DW_CFA_def_cfa */
-		0x04,
-		0x04,
-		0x88,			/* DW_CFA_offset, column 0x8 */
-		0x01,
-		0x00,			/* padding */
-		0x00,
-	/* Now the FDE which contains the instructions for the frame.  */
-		0x22, 0x00, 0x00, 0x00,	/* FDE Length */
-		0x1c, 0x00, 0x00, 0x00,	/* FDE CIE offset */
-	/* The PC-relative offset to the beginning of the code this
-	   FDE covers.  The computation below assumes that the offset
-	   can be represented in one byte.  Change if this is not true
-	   anymore.  The offset from the beginning of the .eh_frame
-	   is represented by EH_FRAME_OFFSET.  The word with the offset
-	   starts at byte 0x20 of the .eh_frame.  */
-		0x100 - (EH_FRAME_OFFSET + 0x20),
-		0xff, 0xff, 0xff,	/* FDE initial location */
-		0x14, 0x00, 0x00, 0x00,	/* FDE address range */
-		0x00,			/* Augmentation size */
-	/* What follows are the instructions for the table generation.
-	   We have to record all changes of the stack pointer and
-	   callee-saved registers.  */
-		0x41,			/* DW_CFA_advance_loc+1, push %ecx */
-		0x0e,			/* DW_CFA_def_cfa_offset */
-		0x08,			/* RA at offset 8 now */
-		0x41,			/* DW_CFA_advance_loc+1, push %edx */
-		0x0e,			/* DW_CFA_def_cfa_offset */
-		0x0c,			/* RA at offset 12 now */
-		0x41,			/* DW_CFA_advance_loc+1, push %ebp */
-		0x0e,			/* DW_CFA_def_cfa_offset */
-		0x10,			/* RA at offset 16 now */
-		0x85, 0x04,		/* DW_CFA_offset %ebp -16 */
-	/* Finally the epilogue.  */
-		0x4e,			/* DW_CFA_advance_loc+14, pop %ebx */
-		0x0e,			/* DW_CFA_def_cfa_offset */
-		0x12,			/* RA at offset 12 now */
-		0xc5,			/* DW_CFA_restore %ebp */
-		0x41,			/* DW_CFA_advance_loc+1, pop %edx */
-		0x0e,			/* DW_CFA_def_cfa_offset */
-		0x08,			/* RA at offset 8 now */
-		0x41,			/* DW_CFA_advance_loc+1, pop %ecx */
-		0x0e,			/* DW_CFA_def_cfa_offset */
-		0x04			/* RA at offset 4 now */
-	};
-	static const char __initdata sigreturn[] = {
-	/* 32: sigreturn point */
-		0x58,				/* popl %eax */
-		0xb8, __NR_sigreturn, 0, 0, 0,	/* movl $__NR_sigreturn, %eax */
-		0xcd, 0x80,			/* int $0x80 */
-	};
-	static const char __initdata rt_sigreturn[] = {
-	/* 64: rt_sigreturn point */
-		0xb8, __NR_rt_sigreturn, 0, 0, 0,	/* movl $__NR_rt_sigreturn, %eax */
-		0xcd, 0x80,			/* int $0x80 */
-	};
 	unsigned long page = get_zeroed_page(GFP_ATOMIC);
 
 	__set_fixmap(FIX_VSYSCALL, __pa(page), PAGE_READONLY);
-	memcpy((void *) page, int80, sizeof(int80));
-	memcpy((void *)(page + 32), sigreturn, sizeof(sigreturn));
-	memcpy((void *)(page + 64), rt_sigreturn, sizeof(rt_sigreturn));
-	memcpy((void *)(page + EH_FRAME_OFFSET), int80_eh_frame,
-	       sizeof(int80_eh_frame));
-	if (!boot_cpu_has(X86_FEATURE_SEP))
+
+	if (!boot_cpu_has(X86_FEATURE_SEP)) {
+		memcpy((void *) page,
+		       &vsyscall_int80_start,
+		       &vsyscall_int80_end - &vsyscall_int80_start);
 		return 0;
+	}
+
+	memcpy((void *) page,
+	       &vsyscall_sysenter_start,
+	       &vsyscall_sysenter_end - &vsyscall_sysenter_start);
 
-	memcpy((void *) page, sysent, sizeof(sysent));
-	memcpy((void *)(page + EH_FRAME_OFFSET), sysent_eh_frame,
-	       sizeof(sysent_eh_frame));
 	on_each_cpu(enable_sep_cpu, NULL, 1, 1);
 	return 0;
 }
--- stock-2.5.68/arch/i386/kernel/vsyscall-int80.S	Wed Dec 31 16:00:00 1969
+++ linux-2.5.68/arch/i386/kernel/vsyscall-int80.S	Wed Apr 23 20:41:41 2003
@@ -0,0 +1,48 @@
+/*
+ * Code for the vsyscall page.  This version uses the old int $0x80 method.
+ */
+
+	.text
+	.globl __kernel_vsyscall
+	.type __kernel_vsyscall,@function
+__kernel_vsyscall:
+.LSTART_vsyscall:
+	int $0x80
+	ret
+.LEND_vsyscall:
+	.size __kernel_vsyscall,.-.LSTART_vsyscall
+	.previous
+
+	.section .eh_frame,"a",@progbits
+.LSTARTFRAMEDLSI:
+	.long .LENDCIEDLSI-.LSTARTCIEDLSI
+.LSTARTCIEDLSI:
+	.long 0			/* CIE ID */
+	.byte 1			/* Version number */
+	.string "zR"		/* NUL-terminated augmentation string */
+	.uleb128 1		/* Code alignment factor */
+	.sleb128 -4		/* Data alignment factor */
+	.byte 8			/* Return address register column */
+	.uleb128 1		/* Augmentation value length */
+	.byte 0x1b		/* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */
+	.byte 0x0c		/* DW_CFA_def_cfa */
+	.uleb128 4
+	.uleb128 4
+	.byte 0x88		/* DW_CFA_offset, column 0x8 */
+	.uleb128 1
+	.align 4
+.LENDCIEDLSI:
+	.long .LENDFDEDLSI-.LSTARTFDEDLSI /* Length FDE */
+.LSTARTFDEDLSI:
+	.long .LSTARTFDEDLSI-.LSTARTFRAMEDLSI /* CIE pointer */
+	.long .LSTART_vsyscall-.	/* PC-relative start address */
+	.long .LEND_vsyscall-.LSTART_vsyscall
+	.uleb128 0
+	.align 4
+.LENDFDEDLSI:
+	.previous
+
+/*
+ * Get the common code for the sigreturn entry points.
+ */
+#include "vsyscall-sigreturn.S"
--- stock-2.5.68/arch/i386/kernel/vsyscall-sysenter.S	Wed Dec 31 16:00:00 1969
+++ linux-2.5.68/arch/i386/kernel/vsyscall-sysenter.S	Wed Apr 23 23:13:14 2003
@@ -0,0 +1,97 @@
+/*
+ * Code for the vsyscall page.  This version uses the sysenter instruction.
+ */
+
+	.text
+	.globl __kernel_vsyscall
+	.type __kernel_vsyscall,@function
+__kernel_vsyscall:
+.LSTART_vsyscall:
+	push %ecx
+.Lpush_ecx:
+	push %edx
+.Lpush_edx:
+	push %ebp
+.Lenter_kernel:
+	movl %esp,%ebp
+	sysenter
+
+	/* 7: align return point with nop's to make disassembly easier */
+	.space 7,0x90
+
+	/* 14: System call restart point is here! (SYSENTER_RETURN - 2) */
+	jmp .Lenter_kernel
+	/* 16: System call normal return point is here! */
+	.globl SYSENTER_RETURN	/* Symbol used by entry.S.  */
+SYSENTER_RETURN:
+	pop %ebp
+.Lpop_ebp:
+	pop %edx
+.Lpop_edx:
+	pop %ecx
+.Lpop_ecx:
+	ret
+.LEND_vsyscall:
+	.size __kernel_vsyscall,.-.LSTART_vsyscall
+	.previous
+
+	.section .eh_frame,"a",@progbits
+.LSTARTFRAMEDLSI:
+	.long .LENDCIEDLSI-.LSTARTCIEDLSI
+.LSTARTCIEDLSI:
+	.long 0			/* CIE ID */
+	.byte 1			/* Version number */
+	.string "zR"		/* NUL-terminated augmentation string */
+	.uleb128 1		/* Code alignment factor */
+	.sleb128 -4		/* Data alignment factor */
+	.byte 8			/* Return address register column */
+	.uleb128 1		/* Augmentation value length */
+	.byte 0x1b		/* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */
+	.byte 0x0c		/* DW_CFA_def_cfa */
+	.uleb128 4
+	.uleb128 4
+	.byte 0x88		/* DW_CFA_offset, column 0x8 */
+	.uleb128 1
+	.align 4
+.LENDCIEDLSI:
+	.long .LENDFDEDLSI-.LSTARTFDEDLSI /* Length FDE */
+.LSTARTFDEDLSI:
+	.long .LSTARTFDEDLSI-.LSTARTFRAMEDLSI /* CIE pointer */
+	.long .LSTART_vsyscall-.	/* PC-relative start address */
+	.long .LEND_vsyscall-.LSTART_vsyscall
+	.uleb128 0
+	/* What follows are the instructions for the table generation.
+	   We have to record all changes of the stack pointer.  */
+	.byte 0x04		/* DW_CFA_advance_loc4 */
+	.long .Lpush_ecx-.LSTART_vsyscall
+	.byte 0x0e		/* DW_CFA_def_cfa_offset */
+	.byte 0x08		/* RA at offset 8 now */
+	.byte 0x04		/* DW_CFA_advance_loc4 */
+	.long .Lpush_edx-.Lpush_ecx
+	.byte 0x0e		/* DW_CFA_def_cfa_offset */
+	.byte 0x0c		/* RA at offset 12 now */
+	.byte 0x04		/* DW_CFA_advance_loc4 */
+	.long .Lenter_kernel-.Lpush_edx
+	.byte 0x0e		/* DW_CFA_def_cfa_offset */
+	.byte 0x10		/* RA at offset 16 now */
+	/* Finally the epilogue.  */
+	.byte 0x04		/* DW_CFA_advance_loc4 */
+	.long .Lpop_ebp-.Lenter_kernel
+	.byte 0x0e		/* DW_CFA_def_cfa_offset */
+	.byte 0x12		/* RA at offset 12 now */
+	.byte 0x04		/* DW_CFA_advance_loc4 */
+	.long .Lpop_edx-.Lpop_ebp
+	.byte 0x0e		/* DW_CFA_def_cfa_offset */
+	.byte 0x08		/* RA at offset 8 now */
+	.byte 0x04		/* DW_CFA_advance_loc4 */
+	.long .Lpop_ecx-.Lpop_edx
+	.byte 0x0e		/* DW_CFA_def_cfa_offset */
+	.byte 0x04		/* RA at offset 4 now */
+	.align 4
+.LENDFDEDLSI:
+	.previous
+
+/*
+ * Get the common code for the sigreturn entry points.
+ */
+#include "vsyscall-sigreturn.S"
--- stock-2.5.68/arch/i386/kernel/vsyscall-sigreturn.S	Wed Dec 31 16:00:00 1969
+++ linux-2.5.68/arch/i386/kernel/vsyscall-sigreturn.S	Wed Apr 23 20:43:16 2003
@@ -0,0 +1,38 @@
+/*
+ * Common code for the sigreturn entry points on the vsyscall page.
+ * So far this code is the same for both int80 and sysenter versions.
+ * This file is #include'd by vsyscall-*.S to define them after the
+ * vsyscall entry point.  The addresses we get for these entry points
+ * by doing ".balign 32" must match in both versions of the page.
+ */
+
+#include <asm/unistd.h>
+
+
+/* XXX
+   Should these be named "_sigtramp" or something?
+*/
+
+	.text
+	.balign 32
+	.globl __kernel_sigreturn
+	.type __kernel_sigreturn,@function
+__kernel_sigreturn:
+.LSTART_kernel_sigreturn:
+	popl %eax		/* XXX does this mean it needs unwind info? */
+	movl $__NR_sigreturn, %eax
+	int $0x80
+.LEND_sigreturn:
+	.size __kernel_sigreturn,.-.LSTART_sigreturn
+
+	.text
+	.balign 32
+	.globl __kernel_rt_sigreturn
+	.type __kernel_rt_sigreturn,@function
+__kernel_rt_sigreturn:
+.LSTART_kernel_rt_sigreturn:
+	movl $__NR_rt_sigreturn, %eax
+	int $0x80
+.LEND_rt_sigreturn:
+	.size __kernel_rt_sigreturn,.-.LSTART_rt_sigreturn
+	.previous
--- stock-2.5.68/arch/i386/kernel/vsyscall.lds	Wed Dec 31 16:00:00 1969
+++ linux-2.5.68/arch/i386/kernel/vsyscall.lds	Wed Apr 23 20:59:12 2003
@@ -0,0 +1,67 @@
+/*
+ * Linker script for vsyscall DSO.  The vsyscall page is an ELF shared
+ * object prelinked to its virtual address, and with only one read-only
+ * segment (that fits in one page).  This script controls its layout.
+ */
+
+/* This must match <asm/fixmap.h>.  */
+VSYSCALL_BASE = 0xffffe000;
+
+SECTIONS
+{
+  . = VSYSCALL_BASE + SIZEOF_HEADERS;
+
+  .hash           : { *(.hash) }		:text
+  .dynsym         : { *(.dynsym) }
+  .dynstr         : { *(.dynstr) }
+  .gnu.version    : { *(.gnu.version) }
+  .gnu.version_d  : { *(.gnu.version_d) }
+  .gnu.version_r  : { *(.gnu.version_r) }
+
+  /* This linker script is used both with -r and with -shared.
+     For the layouts to match, we need to skip more than enough
+     space for the dynamic symbol table et al.  If this amount
+     is insufficient, ld -shared will barf.  Just increase it here.  */
+  . = VSYSCALL_BASE + 0x400;
+
+  .text           : { *(.text) }		:text =0x90909090
+
+  .eh_frame_hdr   : { *(.eh_frame_hdr) }	:text :eh_frame_hdr
+  .eh_frame       : { KEEP (*(.eh_frame)) }	:text
+  .dynamic        : { *(.dynamic) }		:text :dynamic
+  .useless        : {
+  	*(.got.plt) *(.got)
+	*(.data .data.* .gnu.linkonce.d.*)
+	*(.dynbss)
+	*(.bss .bss.* .gnu.linkonce.b.*)
+  }						:text
+}
+
+/*
+ * We must supply the ELF program headers explicitly to get just one
+ * PT_LOAD segment, and set the flags explicitly to make segments read-only.
+ */
+PHDRS
+{
+  text PT_LOAD FILEHDR PHDRS FLAGS(5); /* PF_R|PF_X */
+  dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
+  eh_frame_hdr 0x6474e550; /* PT_GNU_EH_FRAME, but ld doesn't match the name */
+}
+
+/*
+ * This controls what symbols we export from the DSO.
+ */
+VERSION
+{
+  LINUX_2.5 {
+    global:
+    	__kernel_vsyscall;
+    	__kernel_sigreturn;
+    	__kernel_rt_sigreturn;
+
+    local: *;
+  };
+}
+
+/* The ELF entry point can be used to set the AT_SYSINFO value.  */
+ENTRY(__kernel_vsyscall);
--- stock-2.5.68/fs/binfmt_elf.c	Sat Apr 19 19:49:23 2003
+++ linux-2.5.68/fs/binfmt_elf.c	Wed Apr 23 12:54:07 2003
@@ -1260,6 +1260,9 @@ static int elf_core_dump(long signr, str
 	elf_core_copy_regs(&prstatus->pr_reg, regs);
 	
 	segs = current->mm->map_count;
+#ifdef ELF_CORE_EXTRA_PHDRS
+	segs += ELF_CORE_EXTRA_PHDRS;
+#endif
 
 	/* Set up header */
 	fill_elf_header(elf, segs+1);	/* including notes section */
@@ -1340,6 +1343,10 @@ static int elf_core_dump(long signr, str
 		DUMP_WRITE(&phdr, sizeof(phdr));
 	}
 
+#ifdef ELF_CORE_WRITE_EXTRA_PHDRS
+	ELF_CORE_WRITE_EXTRA_PHDRS;
+#endif
+
  	/* write out the notes section */
 	for (i = 0; i < numnote; i++)
 		if (!writenote(notes + i, file))
@@ -1385,6 +1392,10 @@ static int elf_core_dump(long signr, str
 		}
 	}
 
+#ifdef ELF_CORE_WRITE_EXTRA_DATA
+	ELF_CORE_WRITE_EXTRA_DATA;
+#endif
+
 	if ((off_t) file->f_pos != offset) {
 		/* Sanity check */
 		printk("elf_core_dump: file->f_pos (%ld) != offset (%ld)\n",
--- stock-2.5.68/include/linux/elf.h	Sat Apr 19 19:48:52 2003
+++ linux-2.5.68/include/linux/elf.h	Wed Apr 23 02:48:09 2003
@@ -29,8 +29,11 @@ typedef __s64	Elf64_Sxword;
 #define PT_NOTE    4
 #define PT_SHLIB   5
 #define PT_PHDR    6
+#define PT_LOOS	   0x60000000
+#define PT_HIOS	   0x6fffffff
 #define PT_LOPROC  0x70000000
 #define PT_HIPROC  0x7fffffff
+#define PT_GNU_EH_FRAME		0x6474e550
 #define PT_MIPS_REGINFO		0x70000000
 
 /* Flags in the e_flags field of the header */
--- stock-2.5.68/include/asm-i386/elf.h	Sat Apr 19 19:50:08 2003
+++ linux-2.5.68/include/asm-i386/elf.h	Thu Apr 24 17:15:55 2003
@@ -101,7 +101,7 @@ typedef struct user_fxsr_struct elf_fpxr
  * for more of them, start the x86-specific ones at 32.
  */
 #define AT_SYSINFO		32
-#define AT_SYSINFO_EH_FRAME	33
+#define AT_SYSINFO_EHDR		33
 
 #ifdef __KERNEL__
 #define SET_PERSONALITY(ex, ibcs2) set_personality((ibcs2)?PER_SVR4:PER_LINUX)
@@ -119,15 +119,55 @@ extern void dump_smp_unlazy_fpu(void);
 #define ELF_CORE_SYNC dump_smp_unlazy_fpu
 #endif
 
-/* Offset from the beginning of the page where the .eh_frame information
-   for the code in the vsyscall page starts.  */
-#define EH_FRAME_OFFSET 96
+#define VSYSCALL_BASE	(__fix_to_virt(FIX_VSYSCALL))
+#define VSYSCALL_EHDR	((const struct elfhdr *) VSYSCALL_BASE)
+#define VSYSCALL_ENTRY	((unsigned long) &__kernel_vsyscall)
+extern void __kernel_vsyscall;
 
 #define ARCH_DLINFO						\
 do {								\
-		NEW_AUX_ENT(AT_SYSINFO, 0xffffe000);		\
-		NEW_AUX_ENT(AT_SYSINFO_EH_FRAME,		\
-			    0xffffe000 + EH_FRAME_OFFSET);	\
+		NEW_AUX_ENT(AT_SYSINFO,	VSYSCALL_ENTRY);	\
+		NEW_AUX_ENT(AT_SYSINFO_EHDR, VSYSCALL_BASE);	\
+} while (0)
+
+/*
+ * These macros parameterize elf_core_dump in fs/binfmt_elf.c to write out
+ * extra segments containing the vsyscall DSO contents.  Dumping its
+ * contents makes post-mortem fully interpretable later without matching up
+ * the same kernel and hardware config to see what PC values meant.
+ * Dumping its extra ELF program headers includes all the other information
+ * a debugger needs to easily find how the vsyscall DSO was being used.
+ */
+#define ELF_CORE_EXTRA_PHDRS		(VSYSCALL_EHDR->e_phnum)
+#define ELF_CORE_WRITE_EXTRA_PHDRS					      \
+do {									      \
+	const struct elf_phdr *const vsyscall_phdrs =			      \
+		(const struct elf_phdr *) (VSYSCALL_BASE		      \
+					   + VSYSCALL_EHDR->e_phoff);	      \
+	int i;								      \
+	for (i = 0; i < VSYSCALL_EHDR->e_phnum; ++i) {			      \
+		struct elf_phdr phdr = vsyscall_phdrs[i];		      \
+		if (phdr.p_type == PT_LOAD) {				      \
+			phdr.p_offset = offset;				      \
+			offset += phdr.p_filesz;			      \
+		}							      \
+		else							      \
+			phdr.p_offset += offset;			      \
+		phdr.p_paddr = 0; /* match other core phdrs */		      \
+		DUMP_WRITE(&phdr, sizeof(phdr));			      \
+	}								      \
+} while (0)
+#define ELF_CORE_WRITE_EXTRA_DATA					      \
+do {									      \
+	const struct elf_phdr *const vsyscall_phdrs =			      \
+		(const struct elf_phdr *) (VSYSCALL_BASE		      \
+					   + VSYSCALL_EHDR->e_phoff);	      \
+	int i;								      \
+	for (i = 0; i < VSYSCALL_EHDR->e_phnum; ++i) {			      \
+		if (vsyscall_phdrs[i].p_type == PT_LOAD)		      \
+			DUMP_WRITE((void *) vsyscall_phdrs[i].p_vaddr,	      \
+				   vsyscall_phdrs[i].p_filesz);		      \
+	}								      \
 } while (0)
 
 #endif