diff --git a/src/runtime/darwin/signal.c b/src/runtime/darwin/signal.c
index 2325b503cfe..374b6bd6f7c 100644
--- a/src/runtime/darwin/signal.c
+++ b/src/runtime/darwin/signal.c
@@ -64,6 +64,7 @@ sighandler(int32 sig, Siginfo *info, void *context)
 		dumpregs(r);
 	}
 
+	sys·Breakpoint();
 	sys_Exit(2);
 }
 
diff --git a/src/runtime/linux/amd64/defs.h b/src/runtime/linux/amd64/defs.h
index e4c9ec08cac..43b0475239f 100644
--- a/src/runtime/linux/amd64/defs.h
+++ b/src/runtime/linux/amd64/defs.h
@@ -1,48 +1,175 @@
-/*
- *  System structs for Linux, amd64
- */
+// godefs -f -m64 defs.c
 
-typedef uint64 dev_t;
-typedef uint64 ino_t;
-typedef uint32 mode_t;
-typedef uint64 nlink_t;
-typedef uint32 uid_t;
-typedef uint32 gid_t;
-typedef int64 off_t;
-typedef int64 blksize_t;
-typedef int64 blkcnt_t;
-typedef int64 time_t;
+// MACHINE GENERATED - DO NOT EDIT.
 
-struct timespec {
-	time_t tv_sec;
+// Constants
+enum {
+	PROT_NONE = 0,
+	PROT_READ = 0x1,
+	PROT_WRITE = 0x2,
+	PROT_EXEC = 0x4,
+	MAP_ANON = 0x20,
+	MAP_PRIVATE = 0x2,
+	SA_RESTART = 0x10000000,
+	SA_ONSTACK = 0x8000000,
+	SA_RESTORER = 0x4000000,
+	SA_SIGINFO = 0x4,
+};
+
+// Types
+#pragma pack on
+
+typedef struct Timespec Timespec;
+struct Timespec {
+	int64 tv_sec;
 	int64 tv_nsec;
 };
 
-struct timeval {
-	time_t tv_sec;
+typedef struct Timeval Timeval;
+struct Timeval {
+	int64 tv_sec;
 	int64 tv_usec;
 };
 
-struct stat {
-	dev_t	st_dev;     /* ID of device containing file */
-	ino_t	st_ino;     /* inode number */
-	nlink_t	st_nlink;   /* number of hard links */
-	mode_t	st_mode;    /* protection */
-	uid_t	st_uid;     /* user ID of owner */
-	gid_t	st_gid;     /* group ID of owner */
-	int32	pad0;
-	dev_t	st_rdev;    /* device ID (if special file) */
-	off_t	st_size;    /* total size, in bytes */
-	blksize_t st_blksize; /* blocksize for filesystem I/O */
-	blkcnt_t	st_blocks;  /* number of blocks allocated */
-	struct timespec	st_atime;   /* time of last access */
-	struct timespec	st_mtime;   /* time of last modification */
-	struct timespec	st_ctime;   /* time of last status change */
+typedef struct Sigaction Sigaction;
+struct Sigaction {
+	void *sa_handler;
+	uint64 sa_flags;
+	void *sa_restorer;
+	uint64 sa_mask;
 };
 
-#define	O_CREAT	0100
+typedef struct Siginfo Siginfo;
+struct Siginfo {
+	int32 si_signo;
+	int32 si_errno;
+	int32 si_code;
+	byte pad0[4];
+	byte _sifields[112];
+};
+#pragma pack off
+// godefs -f -m64 defs1.c
 
-// Linux-specific system calls
-int64	futex(uint32*, int32, uint32, struct timespec*, uint32*, uint32);
-int64	clone(int32, void*, M*, G*, void(*)(void));
+// MACHINE GENERATED - DO NOT EDIT.
 
+// Constants
+
+// Types
+#pragma pack on
+
+typedef struct Usigset Usigset;
+struct Usigset {
+	uint64 __val[16];
+};
+
+typedef struct Fpxreg Fpxreg;
+struct Fpxreg {
+	uint16 significand[4];
+	uint16 exponent;
+	uint16 padding[3];
+};
+
+typedef struct Xmmreg Xmmreg;
+struct Xmmreg {
+	uint32 element[4];
+};
+
+typedef struct Fpstate Fpstate;
+struct Fpstate {
+	uint16 cwd;
+	uint16 swd;
+	uint16 ftw;
+	uint16 fop;
+	uint64 rip;
+	uint64 rdp;
+	uint32 mxcsr;
+	uint32 mxcr_mask;
+	Fpxreg _st[8];
+	Xmmreg _xmm[16];
+	uint32 padding[24];
+};
+
+typedef struct Fpxreg1 Fpxreg1;
+struct Fpxreg1 {
+	uint16 significand[4];
+	uint16 exponent;
+	uint16 padding[3];
+};
+
+typedef struct Xmmreg1 Xmmreg1;
+struct Xmmreg1 {
+	uint32 element[4];
+};
+
+typedef struct Fpstate1 Fpstate1;
+struct Fpstate1 {
+	uint16 cwd;
+	uint16 swd;
+	uint16 ftw;
+	uint16 fop;
+	uint64 rip;
+	uint64 rdp;
+	uint32 mxcsr;
+	uint32 mxcr_mask;
+	Fpxreg1 _st[8];
+	Xmmreg1 _xmm[16];
+	uint32 padding[24];
+};
+
+typedef struct Sigaltstack Sigaltstack;
+struct Sigaltstack {
+	void *ss_sp;
+	int32 ss_flags;
+	byte pad0[4];
+	uint64 ss_size;
+};
+
+typedef struct Mcontext Mcontext;
+struct Mcontext {
+	int64 gregs[23];
+	Fpstate *fpregs;
+	uint64 __reserved1[8];
+};
+
+typedef struct Ucontext Ucontext;
+struct Ucontext {
+	uint64 uc_flags;
+	Ucontext *uc_link;
+	Sigaltstack uc_stack;
+	Mcontext uc_mcontext;
+	Usigset uc_sigmask;
+	Fpstate __fpregs_mem;
+};
+
+typedef struct Sigcontext Sigcontext;
+struct Sigcontext {
+	uint64 r8;
+	uint64 r9;
+	uint64 r10;
+	uint64 r11;
+	uint64 r12;
+	uint64 r13;
+	uint64 r14;
+	uint64 r15;
+	uint64 rdi;
+	uint64 rsi;
+	uint64 rbp;
+	uint64 rbx;
+	uint64 rdx;
+	uint64 rax;
+	uint64 rcx;
+	uint64 rsp;
+	uint64 rip;
+	uint64 eflags;
+	uint16 cs;
+	uint16 gs;
+	uint16 fs;
+	uint16 __pad0;
+	uint64 err;
+	uint64 trapno;
+	uint64 oldmask;
+	uint64 cr2;
+	Fpstate1 *fpstate;
+	uint64 __reserved1[8];
+};
+#pragma pack off
diff --git a/src/runtime/linux/defs.c b/src/runtime/linux/defs.c
new file mode 100644
index 00000000000..9e635b429a4
--- /dev/null
+++ b/src/runtime/linux/defs.c
@@ -0,0 +1,42 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+ * Input to godefs
+	godefs -f -m64 defs.c >amd64/defs.h
+	godefs -f -m64 defs1.c >>amd64/defs.h
+	godefs defs.c >386/defs.h
+	godefs defs1.c >>386/defs.h
+ */
+
+// Linux glibc and Linux kernel define different and conflicting
+// definitions for struct sigaction, struct timespec, etc.
+// We want the kernel ones, which are in the asm/* headers.
+// But then we'd get conflicts when we include the system
+// headers for things like ucontext_t, so that happens in
+// a separate file, defs1.c.
+
+#include <asm/signal.h>
+#include <asm/siginfo.h>
+#include <asm/mman.h>
+
+enum {
+	$PROT_NONE = PROT_NONE,
+	$PROT_READ = PROT_READ,
+	$PROT_WRITE = PROT_WRITE,
+	$PROT_EXEC = PROT_EXEC,
+
+	$MAP_ANON = MAP_ANONYMOUS,
+	$MAP_PRIVATE = MAP_PRIVATE,
+
+	$SA_RESTART = SA_RESTART,
+	$SA_ONSTACK = SA_ONSTACK,
+	$SA_RESTORER = SA_RESTORER,
+	$SA_SIGINFO = SA_SIGINFO,
+};
+
+typedef struct timespec $Timespec;
+typedef struct timeval $Timeval;
+typedef struct sigaction $Sigaction;
+typedef siginfo_t $Siginfo;
diff --git a/src/runtime/linux/defs1.c b/src/runtime/linux/defs1.c
new file mode 100644
index 00000000000..72de5c1fd63
--- /dev/null
+++ b/src/runtime/linux/defs1.c
@@ -0,0 +1,25 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+ * Input to godefs
+	godefs -f -m64 defs.c >amd64/defs.h
+	godefs -f -m64 defs1.c >>amd64/defs.h
+	godefs defs.c >386/defs.h
+	godefs defs1.c >>386/defs.h
+ */
+
+#include <ucontext.h>
+
+typedef __sigset_t $Usigset;
+typedef struct _libc_fpxreg $Fpxreg;
+typedef struct _libc_xmmreg $Xmmreg;
+typedef struct _libc_fpstate $Fpstate;
+typedef struct _fpxreg $Fpxreg1;
+typedef struct _xmmreg $Xmmreg1;
+typedef struct _fpstate $Fpstate1;
+typedef struct sigaltstack $Sigaltstack;
+typedef mcontext_t $Mcontext;
+typedef ucontext_t $Ucontext;
+typedef struct sigcontext $Sigcontext;
diff --git a/src/runtime/linux/os.h b/src/runtime/linux/os.h
new file mode 100644
index 00000000000..c6161936760
--- /dev/null
+++ b/src/runtime/linux/os.h
@@ -0,0 +1,10 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Linux-specific system calls
+int64	futex(uint32*, int32, uint32, Timespec*, uint32*, uint32);
+int64	clone(int32, void*, M*, G*, void(*)(void));
+
+struct Sigaction;
+void	rt_sigaction(int64, struct Sigaction*, void*, uint64);
diff --git a/src/runtime/linux/signal.c b/src/runtime/linux/signal.c
index 5805f35abf5..87bea263af8 100644
--- a/src/runtime/linux/signal.c
+++ b/src/runtime/linux/signal.c
@@ -5,102 +5,34 @@
 #include "runtime.h"
 #include "defs.h"
 #include "signals.h"
-
-/* From /usr/include/asm-x86_64/sigcontext.h */
-struct _fpstate {
-  uint16   cwd;
-  uint16   swd;
-  uint16   twd;    /* Note this is not the same as the 32bit/x87/FSAVE twd */
-  uint16   fop;
-  uint64   rip;
-  uint32   rdp;
-  uint32   mxcsr;
-  uint32   mxcsr_mask;
-  uint32   st_space[32];   /* 8*16 bytes for each FP-reg */
-  uint32   xmm_space[64];  /* 16*16 bytes for each XMM-reg  */
-  uint32   reserved2[24];
-};
-
-struct sigcontext {
-  uint64 r8;
-  uint64 r9;
-  uint64 r10;
-  uint64 r11;
-  uint64 r12;
-  uint64 r13;
-  uint64 r14;
-  uint64 r15;
-  uint64 rdi;
-  uint64 rsi;
-  uint64 rbp;
-  uint64 rbx;
-  uint64 rdx;
-  uint64 rax;
-  uint64 rcx;
-  uint64 rsp;
-  uint64 rip;
-  uint64 eflags;           /* RFLAGS */
-  uint16 cs;
-  uint16 gs;
-  uint16 fs;
-  uint16 __pad0;
-  uint64 err;
-  uint64 trapno;
-  uint64 oldmask;
-  uint64 cr2;
-  struct _fpstate *fpstate;       /* zero when no FPU context */
-  uint64 reserved1[8];
-};
-
-
-/* From /usr/include/asm-x86_64/signal.h */
-typedef struct sigaltstack {
-	void /*__user*/ *ss_sp;
-	int32 ss_flags;
-	uint64 ss_size;
-} stack_t;
-
-typedef uint64 sigset_t;
-
-
-/* From /usr/include/asm-x86_64/ucontext.h */
-struct ucontext {
-  uint64            uc_flags;
-  struct ucontext  *uc_link;
-  stack_t           uc_stack;
-  struct sigcontext uc_mcontext;
-  sigset_t          uc_sigmask;   /* mask last for extensibility */
-};
-
+#include "os.h"
 
 void
-print_sigcontext(struct sigcontext *sc)
+dumpregs(Sigcontext *r)
 {
-	prints("\nrax     ");  sys·printhex(sc->rax);
-	prints("\nrbx     ");  sys·printhex(sc->rbx);
-	prints("\nrcx     ");  sys·printhex(sc->rcx);
-	prints("\nrdx     ");  sys·printhex(sc->rdx);
-	prints("\nrdi     ");  sys·printhex(sc->rdi);
-	prints("\nrsi     ");  sys·printhex(sc->rsi);
-	prints("\nrbp     ");  sys·printhex(sc->rbp);
-	prints("\nrsp     ");  sys·printhex(sc->rsp);
-	prints("\nr8      ");  sys·printhex(sc->r8 );
-	prints("\nr9      ");  sys·printhex(sc->r9 );
-	prints("\nr10     ");  sys·printhex(sc->r10);
-	prints("\nr11     ");  sys·printhex(sc->r11);
-	prints("\nr12     ");  sys·printhex(sc->r12);
-	prints("\nr13     ");  sys·printhex(sc->r13);
-	prints("\nr14     ");  sys·printhex(sc->r14);
-	prints("\nr15     ");  sys·printhex(sc->r15);
-	prints("\nrip     ");  sys·printhex(sc->rip);
-	prints("\nrflags  ");  sys·printhex(sc->eflags);
-	prints("\ncs      ");  sys·printhex(sc->cs);
-	prints("\nfs      ");  sys·printhex(sc->fs);
-	prints("\ngs      ");  sys·printhex(sc->gs);
-	prints("\n");
+	printf("rax     %X\n", r->rax);
+	printf("rbx     %X\n", r->rbx);
+	printf("rcx     %X\n", r->rcx);
+	printf("rdx     %X\n", r->rdx);
+	printf("rdi     %X\n", r->rdi);
+	printf("rsi     %X\n", r->rsi);
+	printf("rbp     %X\n", r->rbp);
+	printf("rsp     %X\n", r->rsp);
+	printf("r8      %X\n", r->r8 );
+	printf("r9      %X\n", r->r9 );
+	printf("r10     %X\n", r->r10);
+	printf("r11     %X\n", r->r11);
+	printf("r12     %X\n", r->r12);
+	printf("r13     %X\n", r->r13);
+	printf("r14     %X\n", r->r14);
+	printf("r15     %X\n", r->r15);
+	printf("rip     %X\n", r->rip);
+	printf("rflags  %X\n", r->eflags);
+	printf("cs      %X\n", (uint64)r->cs);
+	printf("fs      %X\n", (uint64)r->fs);
+	printf("gs      %X\n", (uint64)r->gs);
 }
 
-
 /*
  * This assembler routine takes the args from registers, puts them on the stack,
  * and calls sighandler().
@@ -109,89 +41,54 @@ extern void sigtramp(void);
 extern void sigignore(void);	// just returns
 extern void sigreturn(void);	// calls sigreturn
 
-/*
- * Rudimentary reverse-engineered definition of signal interface.
- * You'd think it would be documented.
- */
-/* From /usr/include/bits/siginfo.h */
-struct siginfo {
-	int32	si_signo;		/* signal number */
-	int32	si_errno;		/* errno association */
-	int32	si_code;		/* signal code */
-	int32	si_status;		/* exit value */
-	void	*si_addr;		/* faulting address */
-	/* more stuff here */
-};
-
-// This is a struct sigaction from /usr/include/asm/signal.h
-struct sigaction {
-	void (*sa_handler)(int32, struct siginfo*, void*);
-	uint64 sa_flags;
-	void (*sa_restorer)(void);
-	uint64 sa_mask;
-};
-
 void
-sighandler(int32 sig, struct siginfo* info, void** context)
+sighandler(int32 sig, Siginfo* info, void* context)
 {
+	Ucontext *uc;
+	Mcontext *mc;
+	Sigcontext *sc;
+
 	if(panicking)	// traceback already printed
 		sys_Exit(2);
 
-	struct sigcontext *sc = &(((struct ucontext *)context)->uc_mcontext);
+	uc = context;
+	mc = &uc->uc_mcontext;
+	sc = (Sigcontext*)mc;	// same layout, more conveient names
 
-	if(sig < 0 || sig >= NSIG){
-		prints("Signal ");
-		sys·printint(sig);
-	}else{
-		prints(sigtab[sig].name);
-	}
+	if(sig < 0 || sig >= NSIG)
+		printf("Signal %d\n", sig);
+	else
+		printf("%s\n", sigtab[sig].name);
 
-	prints("\nFaulting address: ");  sys·printpointer(info->si_addr);
-	prints("\npc: ");  sys·printhex(sc->rip);
-	prints("\n\n");
+	printf("Faulting address: %p\n", *(void**)info->_sifields);
+	printf("PC=%X\n", sc->rip);
+	printf("\n");
 
 	if(gotraceback()){
-		traceback((void *)sc->rip, (void *)sc->rsp, (void *)sc->r15);
+		traceback((void*)sc->rip, (void*)sc->rsp, (void*)sc->r15);
 		tracebackothers((void*)sc->r15);
-		print_sigcontext(sc);
+		dumpregs(sc);
 	}
 
 	sys·Breakpoint();
 	sys_Exit(2);
 }
 
-struct stack_t {
-	void *sp;
-	int32 flags;
-	int32 pad;
-	int64 size;
-};
-
 void
 signalstack(byte *p, int32 n)
 {
-	struct stack_t st;
+	Sigaltstack st;
 
-	st.sp = p;
-	st.size = n;
-	st.pad = 0;
-	st.flags = 0;
+	st.ss_sp = p;
+	st.ss_size = n;
+	st.ss_flags = 0;
 	sigaltstack(&st, nil);
 }
 
-void	rt_sigaction(int64, void*, void*, uint64);
-
-enum {
-	SA_RESTART = 0x10000000,
-	SA_ONSTACK = 0x08000000,
-	SA_RESTORER = 0x04000000,
-	SA_SIGINFO = 0x00000004,
-};
-
 void
 initsig(void)
 {
-	static struct sigaction sa;
+	static Sigaction sa;
 
 	int32 i;
 	sa.sa_flags = SA_ONSTACK | SA_SIGINFO | SA_RESTORER;
diff --git a/src/runtime/linux/thread.c b/src/runtime/linux/thread.c
index df24b0712d6..4375eca9fcb 100644
--- a/src/runtime/linux/thread.c
+++ b/src/runtime/linux/thread.c
@@ -5,6 +5,7 @@
 #include "runtime.h"
 #include "defs.h"
 #include "signals.h"
+#include "os.h"
 
 // Linux futex.
 //
@@ -24,12 +25,12 @@ enum
 	EAGAIN = 11,
 };
 
-// TODO(rsc) I tried using 1<<40 here but futex woke up (-ETIMEDOUT).
+// TODO(rsc): I tried using 1<<40 here but futex woke up (-ETIMEDOUT).
 // I wonder if the timespec that gets to the kernel
-// actually has two 32-bit numbers in it, so tha
+// actually has two 32-bit numbers in it, so that
 // a 64-bit 1<<40 ends up being 0 seconds,
 // 1<<8 nanoseconds.
-static struct timespec longtime =
+static Timespec longtime =
 {
 	1<<30,	// 34 years
 	0