code review 4230044: runtime: fix signal stack bug

src/pkg/runtime/freebsd/thread.c

 // Use of this source file is governed by a BSD-style
 // license that can be found in the LICENSE file.`
 
 #include "runtime.h"
 #include "defs.h"
 #include "os.h"
+#include "stack.h"
 
 extern SigTab runtime·sigtab[];
 extern int32 runtime·sys_umtx_op(uint32*, int32, uint32, void*, void*);
 
 // FreeBSD's umtx_op syscall is effectively the same as Linux's futex, and
 // thus the code is largely similar. See linux/thread.c for comments.
 
 static void
 umtx_wait(uint32 *addr, uint32 val)
 {
@@ skipping 151 matching lines @@
 {
         runtime·goenvs_unix();
 }
 
 // Called to initialize a new m (including the bootstrap m).
 void
 runtime·minit(void)
 {
         // Initialize signal handling
         m->gsignal = runtime·malg(32*1024);
-        runtime·signalstack(m->gsignal->stackguard, 32*1024);
+        runtime·signalstack(m->gsignal->stackguard - StackGuard, 32*1024);
 }
 
 void
 runtime·sigpanic(void)
 {
         switch(g->sig) {
         case SIGBUS:
                 if(g->sigcode0 == BUS_ADRERR && g->sigcode1 < 0x1000)
                         runtime·panicstring("invalid memory address or nil pointer dereference");
                 runtime·printf("unexpected fault address %p\n", g->sigcode1);
                 runtime·throw("fault");
         case SIGSEGV:
                 if((g->sigcode0 == 0 || g->sigcode0 == SEGV_MAPERR || g->sigcode0 == SEGV_ACCERR) && g->sigcode1 < 0x1000)
                         runtime·panicstring("invalid memory address or nil pointer dereference");
                 runtime·printf("unexpected fault address %p\n", g->sigcode1);
                 runtime·throw("fault");
         case SIGFPE:
                 switch(g->sigcode0) {
                 case FPE_INTDIV:
                         runtime·panicstring("integer divide by zero");
                 case FPE_INTOVF:
                         runtime·panicstring("integer overflow");
                 }
                 runtime·panicstring("floating point error");
         }
         runtime·panicstring(runtime·sigtab[g->sig].name);
 }