[libunwind] Tweak tests for musl support. (#85097)

We can't use `dladdr()` in the tests, because when we're statically
linking with musl that function is a no-op.

Additionally, because musl disables emission of unwind information in
its build, and because its signal trampolines don't include unwind
information, tests that involve unwinding through a signal handler won't
work and need to be disabled for musl.

rdar://123436891

Author: al45tair

libunwind/test/floatregister.pass.cpp

@@ -11,20 +11,27 @@
 
 // Basic test for float registers number are accepted.
 
-#include <dlfcn.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unwind.h>
 
+// Using __attribute__((section("main_func"))) is ELF specific, but then
+// this entire test is marked as requiring Linux, so we should be good.
+//
+// We don't use dladdr() because on musl it's a no-op when statically linked.
+extern char __start_main_func;
+extern char __stop_main_func;
+
 _Unwind_Reason_Code frame_handler(struct _Unwind_Context *ctx, void *arg) {
   (void)arg;
-  Dl_info info = {0, 0, 0, 0};
 
-  // Unwind util the main is reached, above frames depend on the platform and
+  // Unwind until the main is reached, above frames depend on the platform and
   // architecture.
-  if (dladdr(reinterpret_cast<void *>(_Unwind_GetIP(ctx)), &info) &&
-      info.dli_sname && !strcmp("main", info.dli_sname))
+  uintptr_t ip = _Unwind_GetIP(ctx);
+  if (ip >= (uintptr_t)&__start_main_func &&
+      ip < (uintptr_t)&__stop_main_func) {
     _Exit(0);
+  }
 
   return _URC_NO_REASON;
 }
@@ -45,7 +52,7 @@ __attribute__((noinline)) void foo() {
   _Unwind_Backtrace(frame_handler, NULL);
 }
 
-int main() {
+__attribute__((section("main_func"))) int main() {
   foo();
   return -2;
 }

libunwind/test/forceunwind.pass.cpp

@@ -17,7 +17,6 @@
 
 #undef NDEBUG
 #include <assert.h>
-#include <dlfcn.h>
 #include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -27,6 +26,13 @@
 #include <unistd.h>
 #include <unwind.h>
 
+// Using __attribute__((section("main_func"))) is Linux specific, but then
+// this entire test is marked as requiring Linux, so we should be good.
+//
+// We don't use dladdr() because on musl it's a no-op when statically linked.
+extern char __start_main_func;
+extern char __stop_main_func;
+
 void foo();
 _Unwind_Exception ex;
 
@@ -41,14 +47,14 @@ _Unwind_Reason_Code stop(int version, _Unwind_Action actions,
   assert(exceptionObject == &ex);
   assert(stop_parameter == &foo);
 
-  Dl_info info = {0, 0, 0, 0};
-
-  // Unwind util the main is reached, above frames depend on the platform and
+  // Unwind until the main is reached, above frames depend on the platform and
   // architecture.
-  if (dladdr(reinterpret_cast<void *>(_Unwind_GetIP(context)), &info) &&
-      info.dli_sname && !strcmp("main", info.dli_sname)) {
+  uintptr_t ip = _Unwind_GetIP(context);
+  if (ip >= (uintptr_t)&__start_main_func &&
+      ip < (uintptr_t)&__stop_main_func) {
     _Exit(0);
   }
+
   return _URC_NO_REASON;
 }
 
@@ -66,7 +72,7 @@ __attribute__((noinline)) void foo() {
   _Unwind_ForcedUnwind(e, stop, (void *)&foo);
 }
 
-int main() {
+__attribute__((section("main_func"))) int main() {
   foo();
   return -2;
 }

libunwind/test/signal_unwind.pass.cpp

@@ -13,9 +13,15 @@
 // TODO: Figure out why this fails with Memory Sanitizer.
 // XFAIL: msan
 
+// Note: this test fails on musl because:
+//
+//  (a) musl disables emission of unwind information for its build, and
+//  (b) musl's signal trampolines don't include unwind information
+//
+// XFAIL: target={{.*}}-musl
+
 #undef NDEBUG
 #include <assert.h>
-#include <dlfcn.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -24,16 +30,24 @@
 #include <unistd.h>
 #include <unwind.h>
 
+// Using __attribute__((section("main_func"))) is ELF specific, but then
+// this entire test is marked as requiring Linux, so we should be good.
+//
+// We don't use dladdr() because on musl it's a no-op when statically linked.
+extern char __start_main_func;
+extern char __stop_main_func;
+
 _Unwind_Reason_Code frame_handler(struct _Unwind_Context* ctx, void* arg) {
   (void)arg;
-  Dl_info info = { 0, 0, 0, 0 };
 
-  // Unwind util the main is reached, above frames depend on the platform and
+  // Unwind until the main is reached, above frames depend on the platform and
   // architecture.
-  if (dladdr(reinterpret_cast<void *>(_Unwind_GetIP(ctx)), &info) &&
-      info.dli_sname && !strcmp("main", info.dli_sname)) {
+  uintptr_t ip = _Unwind_GetIP(ctx);
+  if (ip >= (uintptr_t)&__start_main_func &&
+      ip < (uintptr_t)&__stop_main_func) {
     _Exit(0);
   }
+
   return _URC_NO_REASON;
 }
 
@@ -43,7 +57,7 @@ void signal_handler(int signum) {
   _Exit(-1);
 }
 
-int main(int, char**) {
+__attribute__((section("main_func"))) int main(int, char **) {
   signal(SIGUSR1, signal_handler);
   kill(getpid(), SIGUSR1);
   return -2;

libunwind/test/unwind_leaffunction.pass.cpp

@@ -13,9 +13,15 @@
 // TODO: Figure out why this fails with Memory Sanitizer.
 // XFAIL: msan
 
+// Note: this test fails on musl because:
+//
+//  (a) musl disables emission of unwind information for its build, and
+//  (b) musl's signal trampolines don't include unwind information
+//
+// XFAIL: target={{.*}}-musl
+
 #undef NDEBUG
 #include <assert.h>
-#include <dlfcn.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -24,16 +30,24 @@
 #include <unistd.h>
 #include <unwind.h>
 
+// Using __attribute__((section("main_func"))) is ELF specific, but then
+// this entire test is marked as requiring Linux, so we should be good.
+//
+// We don't use dladdr() because on musl it's a no-op when statically linked.
+extern char __start_main_func;
+extern char __stop_main_func;
+
 _Unwind_Reason_Code frame_handler(struct _Unwind_Context* ctx, void* arg) {
   (void)arg;
-  Dl_info info = { 0, 0, 0, 0 };
 
   // Unwind until the main is reached, above frames depend on the platform and
   // architecture.
-  if (dladdr(reinterpret_cast<void *>(_Unwind_GetIP(ctx)), &info) &&
-      info.dli_sname && !strcmp("main", info.dli_sname)) {
+  uintptr_t ip = _Unwind_GetIP(ctx);
+  if (ip >= (uintptr_t)&__start_main_func &&
+      ip < (uintptr_t)&__stop_main_func) {
     _Exit(0);
   }
+
   return _URC_NO_REASON;
 }
 
@@ -56,7 +70,7 @@ __attribute__((noinline)) void crashing_leaf_func(int do_trap) {
     __builtin_trap();
 }
 
-int main(int, char**) {
+__attribute__((section("main_func"))) int main(int, char **) {
   signal(SIGTRAP, signal_handler);
   signal(SIGILL, signal_handler);
   crashing_leaf_func(1);