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// 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 <string.h> /* for strerror */
#include <pthread.h>
#include <signal.h>
#include "libcgo.h"
#include "libcgo_unix.h"
static void* threadentry(void*);
static pthread_key_t k1;
#define magic1 (0x23581321U)
static void
inittls(void)
{
uint32 x;
pthread_key_t tofree[128], k;
int i, ntofree;
/*
* Allocate thread-local storage slot for g.
* The key numbers start at 0x100, and we expect to be
* one of the early calls to pthread_key_create, so we
* should be able to get a pretty low number.
*
* In Darwin/386 pthreads, %gs points at the thread
* structure, and each key is an index into the thread-local
* storage array that begins at offset 0x48 within in that structure.
* It may happen that we are not quite the first function to try
* to allocate thread-local storage keys, so instead of depending
* on getting 0x100, we try for 0x108, allocating keys until
* we get the one we want and then freeing the ones we didn't want.
*
* Thus the final offset to use in %gs references is
* 0x48+4*0x108 = 0x468.
*
* The linker and runtime hard-code this constant offset
* from %gs where we expect to find g.
* Known to ../../../liblink/sym.c:/468
* and to ../sys_darwin_386.s:/468
*
* This is truly disgusting and a bit fragile, but taking care
* of it here protects the rest of the system from damage.
* The alternative would be to use a global variable that
* held the offset and refer to that variable each time we
* need a %gs variable (g). That approach would
* require an extra instruction and memory reference in
* every stack growth prolog and would also require
* rewriting the code that 8c generates for extern registers.
*
* Things get more disgusting on OS X 10.7 Lion.
* The 0x48 base mentioned above is the offset of the tsd
* array within the per-thread structure on Leopard and Snow Leopard.
* On Lion, the base moved a little, so while the math above
* still applies, the base is different. Thus, we cannot
* look for specific key values if we want to build binaries
* that run on both systems. Instead, forget about the
* specific key values and just allocate and initialize per-thread
* storage until we find a key that writes to the memory location
* we want. Then keep that key.
*/
ntofree = 0;
for(;;) {
if(pthread_key_create(&k, nil) < 0) {
fprintf(stderr, "runtime/cgo: pthread_key_create failed\n");
abort();
}
pthread_setspecific(k, (void*)magic1);
asm volatile("movl %%gs:0x468, %0" : "=r"(x));
pthread_setspecific(k, 0);
if(x == magic1) {
k1 = k;
break;
}
if(ntofree >= nelem(tofree)) {
fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n");
fprintf(stderr, "\ttried");
for(i=0; i<ntofree; i++)
fprintf(stderr, " %#x", (unsigned)tofree[i]);
fprintf(stderr, "\n");
abort();
}
tofree[ntofree++] = k;
}
/*
* We got the key we wanted. Free the others.
*/
for(i=0; i<ntofree; i++)
pthread_key_delete(tofree[i]);
}
void
x_cgo_init(G *g)
{
pthread_attr_t attr;
size_t size;
pthread_attr_init(&attr);
pthread_attr_getstacksize(&attr, &size);
g->stacklo = (uintptr)&attr - size + 4096;
pthread_attr_destroy(&attr);
inittls();
}
void
_cgo_sys_thread_start(ThreadStart *ts)
{
pthread_attr_t attr;
sigset_t ign, oset;
pthread_t p;
size_t size;
int err;
sigfillset(&ign);
pthread_sigmask(SIG_SETMASK, &ign, &oset);
pthread_attr_init(&attr);
pthread_attr_getstacksize(&attr, &size);
// Leave stacklo=0 and set stackhi=size; mstack will do the rest.
ts->g->stackhi = size;
err = _cgo_try_pthread_create(&p, &attr, threadentry, ts);
pthread_sigmask(SIG_SETMASK, &oset, nil);
if (err != 0) {
fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
abort();
}
}
static void*
threadentry(void *v)
{
ThreadStart ts;
ts = *(ThreadStart*)v;
free(v);
pthread_setspecific(k1, (void*)ts.g);
crosscall_386(ts.fn);
return nil;
}
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