[NFC][Sanitizer] Extract GetFuncAddr from GetRealFunctionAddress

[yln]

Summary

Hopefully, this will enable cleanup/removal of GetRealFunctionAddress in
follow-up commits.

Previous attempt: https://reviews.llvm.org/D59504

[yln]

Update variable name for consistency.

compiler-rt/lib/interception/interception_linux.h

 
 #ifndef INTERCEPTION_LINUX_H
 #define INTERCEPTION_LINUX_H
 
 namespace __interception {
 // returns true if a function with the given name was found.
 bool GetRealFunctionAddress(const char *func_name, uptr *func_addr,
     uptr real, uptr wrapper);
-void *GetFuncAddrVer(const char *func_name, const char *ver);
+void *GetFuncAddr(const char *name);
+void *GetFuncAddrVer(const char *name, const char *ver);
 }  // namespace __interception
 
 #define INTERCEPT_FUNCTION_LINUX_OR_FREEBSD(func)                          \
   ::__interception::GetRealFunctionAddress(                                \
       #func, (::__interception::uptr *)&__interception::PTR_TO_REAL(func), \
       (::__interception::uptr) & (func),                                   \
       (::__interception::uptr) & WRAP(func))
 

compiler-rt/lib/interception/interception_linux.cc

while (true) {
     s1++;
     s2++;
   }
 }
 #endif
 
 bool GetRealFunctionAddress(const char *func_name, uptr *func_addr,
     uptr real, uptr wrapper) {
+  *func_addr = (uptr)GetFuncAddr(func_name);
+  return real == wrapper;
+}
+
+void *GetFuncAddr(const char *name) {
 #if SANITIZER_NETBSD
   // FIXME: Find a better way to handle renames
   if (StrCmp(func_name, "sigaction"))
     func_name = "__sigaction14";
 #endif
-  *func_addr = (uptr)dlsym(RTLD_NEXT, func_name);
-  if (!*func_addr) {
+  void *addr = dlsym(RTLD_NEXT, name);
+  if (!addr) {
     // If the lookup using RTLD_NEXT failed, the sanitizer runtime library is
     // later in the library search order than the DSO that we are trying to
     // intercept, which means that we cannot intercept this function. We still
     // want the address of the real definition, though, so look it up using
     // RTLD_DEFAULT.
-    *func_addr = (uptr)dlsym(RTLD_DEFAULT, func_name);
+    addr = dlsym(RTLD_DEFAULT, name);
   }
-  return real == wrapper;
+  return addr;
 }
 
 // Android and Solaris do not have dlvsym
 #if !SANITIZER_ANDROID && !SANITIZER_SOLARIS && !SANITIZER_OPENBSD
-void *GetFuncAddrVer(const char *func_name, const char *ver) {
-  return dlvsym(RTLD_NEXT, func_name, ver);
+void *GetFuncAddrVer(const char *name, const char *ver) {
+  return dlvsym(RTLD_NEXT, name, ver);
 }
 #endif  // !SANITIZER_ANDROID
 
 }  // namespace __interception
 
 #endif  // SANITIZER_LINUX || SANITIZER_FREEBSD || SANITIZER_NETBSD ||
         // SANITIZER_OPENBSD || SANITIZER_SOLARIS

compiler-rt/lib/interception/tests/interception_linux_test.cc

TEST(Interception, GetRealFunctionAddress) {
   EXPECT_NE(0U, malloc_address);
 
   uptr dummy_address = 0;
   EXPECT_TRUE(
       GetRealFunctionAddress("dummy_doesnt_exist__", &dummy_address, 0, 0));
   EXPECT_EQ(0U, dummy_address);
 }
 
+TEST(Interception, GetFuncAddr) {
+  EXPECT_NE(GetFuncAddr("malloc"), nullptr);
+  EXPECT_EQ(GetFuncAddr("does_not_exist"), nullptr);
+}
+
 TEST(Interception, Basic) {
   ASSERT_TRUE(INTERCEPT_FUNCTION(isdigit));
 
   // After interception, the counter should be incremented.
   InterceptorFunctionCalled = 0;
   EXPECT_NE(0, isdigit('1'));
   EXPECT_EQ(1, InterceptorFunctionCalled);
   EXPECT_EQ(0, isdigit('a'));