diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp
@@ -31,6 +31,9 @@
   Dl_info info;
   int result = dladdr((const void *)addr, &info);
   if (!result) return false;
+
+  CHECK(addr >= reinterpret_cast<uptr>(info.dli_saddr));
+  stack->info.function_offset = addr - reinterpret_cast<uptr>(info.dli_saddr);
   const char *demangled = DemangleSwiftAndCXX(info.dli_sname);
   if (!demangled) return false;
   stack->info.function = internal_strdup(demangled);
@@ -145,12 +148,29 @@
   const char *buf = process_->SendCommand(command);
   if (!buf) return false;
   uptr line;
+  uptr start_address = AddressInfo::kUnknown;
   if (!ParseCommandOutput(buf, addr, &stack->info.function, &stack->info.module,
-                          &stack->info.file, &line, nullptr)) {
+                          &stack->info.file, &line, &start_address)) {
     process_ = nullptr;
     return false;
   }
   stack->info.line = (int)line;
+
+  if (start_address == AddressInfo::kUnknown) {
+    // Fallback to dladdr() to get function start address if atos doesn't report
+    // it.
+    Dl_info info;
+    int result = dladdr((const void *)addr, &info);
+    if (result)
+      start_address = reinterpret_cast<uptr>(info.dli_saddr);
+  }
+
+  // Only assig to `function_offset` if we were able to get the function's
+  // start address.
+  if (start_address != AddressInfo::kUnknown) {
+    CHECK(addr >= start_address);
+    stack->info.function_offset = addr - start_address;
+  }
   return true;
 }
 
diff --git a/compiler-rt/test/asan/TestCases/Darwin/asan-symbolize-partial-report-no-external-symbolizer.cpp b/compiler-rt/test/asan/TestCases/Darwin/asan-symbolize-partial-report-no-external-symbolizer.cpp
--- a/compiler-rt/test/asan/TestCases/Darwin/asan-symbolize-partial-report-no-external-symbolizer.cpp
+++ b/compiler-rt/test/asan/TestCases/Darwin/asan-symbolize-partial-report-no-external-symbolizer.cpp
@@ -17,8 +17,8 @@
 // source location is not and instead module name and offset are
 // printed.
 // CHECK-PS: WRITE of size 4
-// CHECK-PS: #0 0x{{.+}} in foo ({{.+}}.executable:{{.+}}+0x{{.+}})
-// CHECK-PS: #1 0x{{.+}} in main ({{.+}}.executable:{{.+}}+0x{{.+}})
+// CHECK-PS: #0 0x{{.+}} in foo{{(\+0x[0-9a-f]+)?}} ({{.+}}.executable:{{.+}}+0x{{.+}})
+// CHECK-PS: #1 0x{{.+}} in main{{(\+0x[0-9a-f]+)?}} ({{.+}}.executable:{{.+}}+0x{{.+}})
 
 // CHECK-FS: WRITE of size 4
 
diff --git a/compiler-rt/test/sanitizer_common/TestCases/Darwin/symbolizer-function-offset-atos.cpp b/compiler-rt/test/sanitizer_common/TestCases/Darwin/symbolizer-function-offset-atos.cpp
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/sanitizer_common/TestCases/Darwin/symbolizer-function-offset-atos.cpp
@@ -0,0 +1,43 @@
+// RUN: %clangxx %s -g -O0 -o %t-with-debug
+
+// With debug info atos reports the source location, but no function offset. We fallback to dladdr() to retrieve the function offset.
+// RUN: %env_tool_opts=verbosity=2,stack_trace_format='"function_name:%f function_offset:%q"' %run %t-with-debug > %t-with-debug.output 2>&1
+// RUN: FileCheck -input-file=%t-with-debug.output %s
+
+// Without debug info atos reports the function offset and so dladdr() fallback is not used.
+// RUN: rm -rf %t-with-debug.dSYM
+// RUN: %env_tool_opts=verbosity=2,stack_trace_format='"function_name:%f function_offset:%q"' %run %t-with-debug > %t-no-debug.output 2>&1
+// RUN: FileCheck -input-file=%t-no-debug.output %s
+
+#include <sanitizer/common_interface_defs.h>
+#include <stdio.h>
+
+void baz() {
+  printf("Do stuff in baz\n");
+  __sanitizer_print_stack_trace();
+}
+
+void bar() {
+  printf("Do stuff in bar\n");
+  baz();
+}
+
+void foo() {
+  printf("Do stuff in foo\n");
+  bar();
+}
+
+int main() {
+  printf("Do stuff in main\n");
+  foo();
+  return 0;
+}
+
+// CHECK: Using atos found at:
+
+// These `function_offset` patterns are designed to disallow `0x0` which is the
+// value printed for `kUnknown`.
+// CHECK: function_name:baz{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
+// CHECK: function_name:bar{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
+// CHECK: function_name:foo{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
+// CHECK: function_name:main{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
diff --git a/compiler-rt/test/sanitizer_common/TestCases/Darwin/symbolizer-function-offset-dladdr.cpp b/compiler-rt/test/sanitizer_common/TestCases/Darwin/symbolizer-function-offset-dladdr.cpp
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/sanitizer_common/TestCases/Darwin/symbolizer-function-offset-dladdr.cpp
@@ -0,0 +1,41 @@
+// UNSUPPORTED: lsan
+// This test fails with LSan enabled because the dladdr symbolizer actually leaks
+// memory because the call to `__sanitizer::DemangleCXXABI` leaks memory which LSan
+// detects (rdar://problem/42868950).
+
+// RUN: %clangxx %s -O0 -o %t
+// RUN: %env_tool_opts=verbosity=2,external_symbolizer_path=,stack_trace_format='"function_name:%f function_offset:%q"' %run %t > %t.output 2>&1
+// RUN: FileCheck -input-file=%t.output %s
+#include <sanitizer/common_interface_defs.h>
+#include <stdio.h>
+
+void baz() {
+  printf("Do stuff in baz\n");
+  __sanitizer_print_stack_trace();
+}
+
+void bar() {
+  printf("Do stuff in bar\n");
+  baz();
+}
+
+void foo() {
+  printf("Do stuff in foo\n");
+  bar();
+}
+
+int main() {
+  printf("Do stuff in main\n");
+  foo();
+  return 0;
+}
+
+// CHECK: External symbolizer is explicitly disabled
+// CHECK: Using dladdr symbolizer
+
+// These `function_offset` patterns are designed to disallow `0x0` which is the
+// value printed for `kUnknown`.
+// CHECK: function_name:baz{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
+// CHECK: function_name:bar{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
+// CHECK: function_name:foo{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}
+// CHECK: function_name:main{{(\(\))?}} function_offset:0x{{0*[1-9a-f][0-9a-f]*$}}