src/runtime/rt1_amd64_linux.c

// 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.

#include "runtime.h"
#include "amd64_linux.h"
#include "signals_linux.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 */
};


void
print_sigcontext(struct sigcontext *sc)
{
	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");
}


/*
 * This assembler routine takes the args from registers, puts them on the stack,
 * and calls sighandler().
 */
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)
{
	if(panicking)	// traceback already printed
		sys·exit(2);

	struct sigcontext *sc = &(((struct ucontext *)context)->uc_mcontext);

	if(sig < 0 || sig >= NSIG){
		prints("Signal ");
		sys·printint(sig);
	}else{
		prints(sigtab[sig].name);
	}

	prints("\nFaulting address: ");  sys·printpointer(info->si_addr);
	prints("\npc: ");  sys·printhex(sc->rip);
	prints("\n\n");

	if(gotraceback()){
		traceback((void *)sc->rip, (void *)sc->rsp, (void *)sc->r15);
		tracebackothers((void*)sc->r15);
		print_sigcontext(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;

	st.sp = p;
	st.size = n;
	st.pad = 0;
	st.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;

	int32 i;
	sa.sa_flags = SA_ONSTACK | SA_SIGINFO | SA_RESTORER;
	sa.sa_mask = 0xFFFFFFFFFFFFFFFFULL;
	sa.sa_restorer = (void*)sigreturn;
	for(i = 0; i<NSIG; i++) {
		if(sigtab[i].flags) {
			if(sigtab[i].flags & SigCatch)
				sa.sa_handler = (void*)sigtramp;
			else
				sa.sa_handler = (void*)sigignore;
			if(sigtab[i].flags & SigRestart)
				sa.sa_flags |= SA_RESTART;
			else
				sa.sa_flags &= ~SA_RESTART;
			rt_sigaction(i, &sa, nil, 8);
		}
	}
}


// Linux futex.
//
//	futexsleep(uint32 *addr, uint32 val)
//	futexwakeup(uint32 *addr)
//
// Futexsleep atomically checks if *addr == val and if so, sleeps on addr.
// Futexwakeup wakes up one thread sleeping on addr.
// Futexsleep is allowed to wake up spuriously.

enum
{
	FUTEX_WAIT = 0,
	FUTEX_WAKE = 1,

	EINTR = 4,
	EAGAIN = 11,
};

// 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
// a 64-bit 1<<40 ends up being 0 seconds,
// 1<<8 nanoseconds.
static struct timespec longtime =
{
	1<<30,	// 34 years
	0
};

// Atomically,
//	if(*addr == val) sleep
// Might be woken up spuriously; that's allowed.
static void
futexsleep(uint32 *addr, uint32 val)
{
	int64 ret;

	ret = futex(addr, FUTEX_WAIT, val, &longtime, nil, 0);
	if(ret >= 0 || ret == -EAGAIN || ret == -EINTR)
		return;

	prints("futexsleep addr=");
	sys·printpointer(addr);
	prints(" val=");
	sys·printint(val);
	prints(" returned ");
	sys·printint(ret);
	prints("\n");
	*(int32*)0x1005 = 0x1005;
}

// If any procs are sleeping on addr, wake up at least one.
static void
futexwakeup(uint32 *addr)
{
	int64 ret;

	ret = futex(addr, FUTEX_WAKE, 1, nil, nil, 0);

	if(ret >= 0)
		return;

	// I don't know that futex wakeup can return
	// EAGAIN or EINTR, but if it does, it would be
	// safe to loop and call futex again.

	prints("futexwakeup addr=");
	sys·printpointer(addr);
	prints(" returned ");
	sys·printint(ret);
	prints("\n");
	*(int32*)0x1006 = 0x1006;
}


// Lock and unlock.
//
// The lock state is a single 32-bit word that holds
// a 31-bit count of threads waiting for the lock
// and a single bit (the low bit) saying whether the lock is held.
// The uncontended case runs entirely in user space.
// When contention is detected, we defer to the kernel (futex).
//
// A reminder: compare-and-swap cas(addr, old, new) does
//	if(*addr == old) { *addr = new; return 1; }
// 	else return 0;
// but atomically.

void
lock(Lock *l)
{
	uint32 v;

again:
	v = l->key;
	if((v&1) == 0){
		if(cas(&l->key, v, v|1)){
			// Lock wasn't held; we grabbed it.
			return;
		}
		goto again;
	}

	// Lock was held; try to add ourselves to the waiter count.
	if(!cas(&l->key, v, v+2))
		goto again;

	// We're accounted for, now sleep in the kernel.
	//
	// We avoid the obvious lock/unlock race because
	// the kernel won't put us to sleep if l->key has
	// changed underfoot and is no longer v+2.
	//
	// We only really care that (v&1) == 1 (the lock is held),
	// and in fact there is a futex variant that could
	// accomodate that check, but let's not get carried away.)
	futexsleep(&l->key, v+2);

	// We're awake: remove ourselves from the count.
	for(;;){
		v = l->key;
		if(v < 2)
			throw("bad lock key");
		if(cas(&l->key, v, v-2))
			break;
	}

	// Try for the lock again.
	goto again;
}

void
unlock(Lock *l)
{
	uint32 v;

	// Atomically get value and clear lock bit.
again:
	v = l->key;
	if((v&1) == 0)
		throw("unlock of unlocked lock");
	if(!cas(&l->key, v, v&~1))
		goto again;

	// If there were waiters, wake one.
	if(v & ~1)
		futexwakeup(&l->key);
}


// One-time notifications.
//
// Since the lock/unlock implementation already
// takes care of sleeping in the kernel, we just reuse it.
// (But it's a weird use, so it gets its own interface.)
//
// We use a lock to represent the event:
// unlocked == event has happened.
// Thus the lock starts out locked, and to wait for the
// event you try to lock the lock.  To signal the event,
// you unlock the lock.

void
noteclear(Note *n)
{
	n->lock.key = 0;	// memset(n, 0, sizeof *n)
	lock(&n->lock);
}

void
notewakeup(Note *n)
{
	unlock(&n->lock);
}

void
notesleep(Note *n)
{
	lock(&n->lock);
	unlock(&n->lock);	// Let other sleepers find out too.
}


// Clone, the Linux rfork.
enum
{
	CLONE_VM = 0x100,
	CLONE_FS = 0x200,
	CLONE_FILES = 0x400,
	CLONE_SIGHAND = 0x800,
	CLONE_PTRACE = 0x2000,
	CLONE_VFORK = 0x4000,
	CLONE_PARENT = 0x8000,
	CLONE_THREAD = 0x10000,
	CLONE_NEWNS = 0x20000,
	CLONE_SYSVSEM = 0x40000,
	CLONE_SETTLS = 0x80000,
	CLONE_PARENT_SETTID = 0x100000,
	CLONE_CHILD_CLEARTID = 0x200000,
	CLONE_UNTRACED = 0x800000,
	CLONE_CHILD_SETTID = 0x1000000,
	CLONE_STOPPED = 0x2000000,
	CLONE_NEWUTS = 0x4000000,
	CLONE_NEWIPC = 0x8000000,
};

void
newosproc(M *m, G *g, void *stk, void (*fn)(void))
{
	int64 ret;
	int32 flags;

	flags = CLONE_PARENT	/* getppid doesn't change in child */
		| CLONE_VM	/* share memory */
		| CLONE_FS	/* share cwd, etc */
		| CLONE_FILES	/* share fd table */
		| CLONE_SIGHAND	/* share sig handler table */
		| CLONE_PTRACE	/* revisit - okay for now */
		| CLONE_THREAD	/* revisit - okay for now */
		;

	if(0){
		prints("newosproc stk=");
		sys·printpointer(stk);
		prints(" m=");
		sys·printpointer(m);
		prints(" g=");
		sys·printpointer(g);
		prints(" fn=");
		sys·printpointer(fn);
		prints(" clone=");
		sys·printpointer(clone);
		prints("\n");
	}

	ret = clone(flags, stk, m, g, fn);
	if(ret < 0)
		*(int32*)123 = 123;
}

void
osinit(void)
{
}

// Called to initialize a new m (including the bootstrap m).
void
minit(void)
{
	// Initialize signal handling.
	m->gsignal = malg(32*1024);	// OS X wants >=8K, Linux >=2K
	signalstack(m->gsignal->stackguard, 32*1024);
}