It turns out that asm/reg.h is missing from the 2.6.x kernel headers,

which prevents libthread_db (used by gdb) from compiling.  Include a
copy within include/sys/user.h for mips, per what was done in glibc.

libc/sysdeps/linux/mips/sys/user.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2002 Free Software Foundation, Inc.
+/* Copyright (C) 2002, 2003 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
@@ -23,7 +23,154 @@
    too much into it.  Don't use it for anything other than GDB unless
    you know what you are doing.  */
 
-#include <asm/reg.h>
+/* #include <asm/reg.h> */
+/* Instead of including the kernel header, that will vary depending on
+   whether the 32- or the 64-bit kernel is installed, we paste its
+   contents here.  Note that the fact that the file is inline here,
+   instead of included separately, doesn't change in any way the
+   licensing status of a program that includes user.h.  Since this is
+   for gdb alone, and gdb is GPLed, no surprises here.  */
+#if _MIPS_SIM == _MIPS_SIM_ABI32
+/*
+ * Various register offset definitions for debuggers, core file
+ * examiners and whatnot.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1995, 1999 by Ralf Baechle
+ */
+#ifndef __ASM_MIPS_REG_H
+#define __ASM_MIPS_REG_H
+
+/*
+ * This defines/structures correspond to the register layout on stack -
+ * if the order here is changed, it needs to be updated in
+ * include/asm-mips/stackframe.h
+ */
+#define EF_REG0			6
+#define EF_REG1			7
+#define EF_REG2			8
+#define EF_REG3			9
+#define EF_REG4			10
+#define EF_REG5			11
+#define EF_REG6			12
+#define EF_REG7			13
+#define EF_REG8			14
+#define EF_REG9			15
+#define EF_REG10		16
+#define EF_REG11		17
+#define EF_REG12		18
+#define EF_REG13		19
+#define EF_REG14		20
+#define EF_REG15		21
+#define EF_REG16		22
+#define EF_REG17		23
+#define EF_REG18		24
+#define EF_REG19		25
+#define EF_REG20		26
+#define EF_REG21		27
+#define EF_REG22		28
+#define EF_REG23		29
+#define EF_REG24		30
+#define EF_REG25		31
+/*
+ * k0/k1 unsaved
+ */
+#define EF_REG28		34
+#define EF_REG29		35
+#define EF_REG30		36
+#define EF_REG31		37
+
+/*
+ * Saved special registers
+ */
+#define EF_LO			38
+#define EF_HI			39
+
+#define EF_CP0_EPC		40
+#define EF_CP0_BADVADDR		41
+#define EF_CP0_STATUS		42
+#define EF_CP0_CAUSE		43
+
+#define EF_SIZE			180	/* size in bytes */
+
+#endif /* __ASM_MIPS_REG_H */
+
+#else /* _MIPS_SIM != _MIPS_SIM_ABI32 */
+
+/*
+ * Various register offset definitions for debuggers, core file
+ * examiners and whatnot.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1995, 1999 Ralf Baechle
+ * Copyright (C) 1995, 1999 Silicon Graphics
+ */
+#ifndef _ASM_REG_H
+#define _ASM_REG_H
+
+/*
+ * This defines/structures correspond to the register layout on stack -
+ * if the order here is changed, it needs to be updated in
+ * include/asm-mips/stackframe.h
+ */
+#define EF_REG0			 0
+#define EF_REG1			 1
+#define EF_REG2			 2
+#define EF_REG3			 3
+#define EF_REG4			 4
+#define EF_REG5			 5
+#define EF_REG6			 6
+#define EF_REG7			 7
+#define EF_REG8			 8
+#define EF_REG9			 9
+#define EF_REG10		10
+#define EF_REG11		11
+#define EF_REG12		12
+#define EF_REG13		13
+#define EF_REG14		14
+#define EF_REG15		15
+#define EF_REG16		16
+#define EF_REG17		17
+#define EF_REG18		18
+#define EF_REG19		19
+#define EF_REG20		20
+#define EF_REG21		21
+#define EF_REG22		22
+#define EF_REG23		23
+#define EF_REG24		24
+#define EF_REG25		25
+/*
+ * k0/k1 unsaved
+ */
+#define EF_REG28		28
+#define EF_REG29		29
+#define EF_REG30		30
+#define EF_REG31		31
+
+/*
+ * Saved special registers
+ */
+#define EF_LO			32
+#define EF_HI			33
+
+#define EF_CP0_EPC		34
+#define EF_CP0_BADVADDR		35
+#define EF_CP0_STATUS		36
+#define EF_CP0_CAUSE		37
+
+#define EF_SIZE			304	/* size in bytes */
+
+#endif /* _ASM_REG_H */
+
+#endif /* _MIPS_SIM != _MIPS_SIM_ABI32 */
+
+#if _MIPS_SIM == _MIPS_SIM_ABI32
 
 struct user
 {
@@ -40,6 +187,24 @@ struct user
   char		u_comm[32];		/* user command name */
 };
 
+#else
+
+struct user {
+  __extension__ unsigned long	regs[EF_SIZE/8+64]; /* integer and fp regs */
+  __extension__ unsigned long	u_tsize;	/* text size (pages) */
+  __extension__ unsigned long	u_dsize;	/* data size (pages) */
+  __extension__ unsigned long	u_ssize;	/* stack size (pages) */
+  __extension__ unsigned long long start_code;	/* text starting address */
+  __extension__ unsigned long long start_data;	/* data starting address */
+  __extension__ unsigned long long start_stack;	/* stack starting address */
+  __extension__ long long	signal;		/* signal causing core dump */
+  __extension__ unsigned long long u_ar0;	/* help gdb find registers */
+  __extension__ unsigned long long magic;	/* identifies a core file */
+  char		u_comm[32];		/* user command name */
+};
+
+#endif
+
 #define PAGE_SHIFT		12
 #define PAGE_SIZE		(1UL << PAGE_SHIFT)
 #define PAGE_MASK		(~(PAGE_SIZE-1))