github.com/aloncn/graphics-go@v0.0.1/src/runtime/cgo/gcc_darwin_386.c (about)

     1  // Copyright 2009 The Go Authors.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build cgo
     6  
     7  #include <string.h> /* for strerror */
     8  #include <pthread.h>
     9  #include <signal.h>
    10  #include "libcgo.h"
    11  
    12  static void* threadentry(void*);
    13  static pthread_key_t k1;
    14  
    15  #define magic1 (0x23581321U)
    16  
    17  static void
    18  inittls(void)
    19  {
    20  	uint32 x;
    21  	pthread_key_t tofree[128], k;
    22  	int i, ntofree;
    23  
    24  	/*
    25  	 * Allocate thread-local storage slot for g.
    26  	 * The key numbers start at 0x100, and we expect to be
    27  	 * one of the early calls to pthread_key_create, so we
    28  	 * should be able to get a pretty low number.
    29  	 *
    30  	 * In Darwin/386 pthreads, %gs points at the thread
    31  	 * structure, and each key is an index into the thread-local
    32  	 * storage array that begins at offset 0x48 within in that structure.
    33  	 * It may happen that we are not quite the first function to try
    34  	 * to allocate thread-local storage keys, so instead of depending
    35  	 * on getting 0x100, we try for 0x108, allocating keys until
    36  	 * we get the one we want and then freeing the ones we didn't want.
    37  	 *
    38  	 * Thus the final offset to use in %gs references is
    39  	 * 0x48+4*0x108 = 0x468.
    40  	 *
    41  	 * The linker and runtime hard-code this constant offset
    42  	 * from %gs where we expect to find g.
    43  	 * Known to ../../../liblink/sym.c:/468
    44  	 * and to ../sys_darwin_386.s:/468
    45  	 *
    46  	 * This is truly disgusting and a bit fragile, but taking care
    47  	 * of it here protects the rest of the system from damage.
    48  	 * The alternative would be to use a global variable that
    49  	 * held the offset and refer to that variable each time we
    50  	 * need a %gs variable (g).  That approach would
    51  	 * require an extra instruction and memory reference in
    52  	 * every stack growth prolog and would also require
    53  	 * rewriting the code that 8c generates for extern registers.
    54  	 *
    55  	 * Things get more disgusting on OS X 10.7 Lion.
    56  	 * The 0x48 base mentioned above is the offset of the tsd
    57  	 * array within the per-thread structure on Leopard and Snow Leopard.
    58  	 * On Lion, the base moved a little, so while the math above
    59  	 * still applies, the base is different.  Thus, we cannot
    60  	 * look for specific key values if we want to build binaries
    61  	 * that run on both systems.  Instead, forget about the
    62  	 * specific key values and just allocate and initialize per-thread
    63  	 * storage until we find a key that writes to the memory location
    64  	 * we want.  Then keep that key.
    65  	 */
    66  	ntofree = 0;
    67  	for(;;) {
    68  		if(pthread_key_create(&k, nil) < 0) {
    69  			fprintf(stderr, "runtime/cgo: pthread_key_create failed\n");
    70  			abort();
    71  		}
    72  		pthread_setspecific(k, (void*)magic1);
    73  		asm volatile("movl %%gs:0x468, %0" : "=r"(x));
    74  		pthread_setspecific(k, 0);
    75  		if(x == magic1) {
    76  			k1 = k;
    77  			break;
    78  		}
    79  		if(ntofree >= nelem(tofree)) {
    80  			fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n");
    81  			fprintf(stderr, "\ttried");
    82  			for(i=0; i<ntofree; i++)
    83  				fprintf(stderr, " %#x", (unsigned)tofree[i]);
    84  			fprintf(stderr, "\n");
    85  			abort();
    86  		}
    87  		tofree[ntofree++] = k;
    88  	}
    89  
    90  	/*
    91  	 * We got the key we wanted.  Free the others.
    92  	 */
    93  	for(i=0; i<ntofree; i++)
    94  		pthread_key_delete(tofree[i]);
    95  }
    96  
    97  void
    98  x_cgo_init(G *g)
    99  {
   100  	pthread_attr_t attr;
   101  	size_t size;
   102  
   103  	pthread_attr_init(&attr);
   104  	pthread_attr_getstacksize(&attr, &size);
   105  	g->stacklo = (uintptr)&attr - size + 4096;
   106  	pthread_attr_destroy(&attr);
   107  
   108  	inittls();
   109  }
   110  
   111  
   112  void
   113  _cgo_sys_thread_start(ThreadStart *ts)
   114  {
   115  	pthread_attr_t attr;
   116  	sigset_t ign, oset;
   117  	pthread_t p;
   118  	size_t size;
   119  	int err;
   120  
   121  	sigfillset(&ign);
   122  	pthread_sigmask(SIG_SETMASK, &ign, &oset);
   123  
   124  	pthread_attr_init(&attr);
   125  	pthread_attr_getstacksize(&attr, &size);
   126  	// Leave stacklo=0 and set stackhi=size; mstack will do the rest.
   127  	ts->g->stackhi = size;
   128  	err = pthread_create(&p, &attr, threadentry, ts);
   129  
   130  	pthread_sigmask(SIG_SETMASK, &oset, nil);
   131  
   132  	if (err != 0) {
   133  		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
   134  		abort();
   135  	}
   136  }
   137  
   138  static void*
   139  threadentry(void *v)
   140  {
   141  	ThreadStart ts;
   142  
   143  	ts = *(ThreadStart*)v;
   144  	free(v);
   145  
   146  	pthread_setspecific(k1, (void*)ts.g);
   147  
   148  	crosscall_386(ts.fn);
   149  	return nil;
   150  }