[TSan] fix Go runtime test on amd64 with PIE

[pelikan]

Summary

Without this diff, the test segfaults. Examining the generated executable
(which gets auto-deleted likely by cmake/ninja) yields this error message:

ThreadSanitizer failed to allocate 0x4000 (16384) bytes at address 1755558480000 (errno: 12)

Note that the address has more than 47 bits, which on amd64 means special
treatment and therefore points out an overflow. The allocation came from
__tsan_map_shadow on a .data pointer, which (on my work Debian-based box)
means the 0x550000000000 range. This doesn't correspond to the constants
mentioned in tsan_platform.h for Go binaries on Linux/amd64.

The diff therefore allocates memory in the sort of area Go programs would,
and prevents the test from crashing. It would be nice if reviewers kindly
considered other setups and architectures :-)

[pelikan]

add errno printout, in case something goes wrong on the buildbots

[dvyukov]

LGTM
It actually fails on my laptop in the same way now. But works with this patch.

[pelikan]

sync to HEAD

[pelikan]

sync again - something's wrong with Git

[pelikan]

sync again?

compiler-rt/trunk/lib/tsan/go/test.c

 //===-- test.c ------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Sanity test for Go runtime.
 //
 //===----------------------------------------------------------------------===//
 
+#include <sys/mman.h>
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 void __tsan_init(void **thr, void **proc, void (*cb)(long, void*));
 void __tsan_fini();
 void __tsan_map_shadow(void *addr, unsigned long size);
 void __tsan_go_start(void *thr, void **chthr, void *pc);
 void __tsan_go_end(void *thr);
void symbolize_cb(long cmd, void *ctx) {
   switch (cmd) {
   case 0:
     if (current_proc == 0)
       abort();
     *(void**)ctx = current_proc;
   }
 }
 
-char buf0[100<<10];
+/*
+ * See lib/tsan/rtl/tsan_platform.h for details of what the memory layout
+ * of Go programs looks like.  To prevent running over existing mappings,
+ * we pick an address slightly inside the Go heap region.
+ */
+void *go_heap = (void *)0xC011110000;
+char *buf0;
 
 void foobar() {}
 void barfoo() {}
 
 int main(void) {
   void *thr0 = 0;
   void *proc0 = 0;
   __tsan_init(&thr0, &proc0, symbolize_cb);
   current_proc = proc0;
+
+  // Allocate something resembling a heap in Go.
+  buf0 = mmap(go_heap, 16384, PROT_READ | PROT_WRITE,
+              MAP_PRIVATE | MAP_FIXED | MAP_ANON, -1, 0);
+  if (buf0 == MAP_FAILED) {
+    fprintf(stderr, "failed to allocate Go-like heap at %p; errno %d\n",
+            go_heap, errno);
+    return 1;
+  }
   char *buf = (char*)((unsigned long)buf0 + (64<<10) - 1 & ~((64<<10) - 1));
   __tsan_map_shadow(buf, 4096);
   __tsan_malloc(thr0, (char*)&barfoo + 1, buf, 10);
   __tsan_free(buf, 10);
   __tsan_func_enter(thr0, (char*)&main + 1);
   __tsan_malloc(thr0, (char*)&barfoo + 1, buf, 10);
   __tsan_release(thr0, buf);
   __tsan_release_merge(thr0, buf);