libclang/CIndexer.cpp: Use loadquery() on AIX for path to library

[hubert.reinterpretcast]

Summary

dladdr is not available on AIX. Similar functionality is presented through loadquery. This patch replaces a use of dladdr with a version based on loadquery.

[hubert.reinterpretcast]

I believe that the conditions being checked for with llvm_unreachable in this patch are of the debug-only variety; however, some input would be appreciated regarding the choice of using llvm_unreachable instead of report_fatal_error or assert.

tools/libclang/CIndexer.cpp

61

Based on available documentation, this situation should not occur (and thus I believe llvm_unreachable is appropriate).

65

This situation is not impossible, but highly improbable. This is a non-programmatic error, and the Programmer's Manual appears to recommend the use of report_fatal_error. Some additional guidance would be appreciated.

84

This is also supposed to not happen.

[xingxue]

LGTM. Thanks!

[hubert.reinterpretcast]

@asb @lhames @majnemer, based on D36826, I believe that your guidance would be helpful here regarding the use of llvm_unreachable, report_fatal_error, and assert.

[hubert.reinterpretcast]

Thanks @xingxue for the review. I will update for the error handling before committing.

tools/libclang/CIndexer.cpp

61

I'll leave this one as llvm_unreachable, either the failure is resolved on a later call or the loop will terminate when the amount of memory to request (checked below) is too large.

65

I will change this to report_fatal_error.

84

I will change this to report_fatal_error. Infinite loops are unfriendly.

[asb]

In D59233#1439656, @hubert.reinterpretcast wrote:

Thanks @xingxue for the review. I will update for the error handling before committing.

Use of report_fatal_error/llvm_unreachable isn't fully consistent within the LLVM codebase, but I think your choices here are sensible.

tools/libclang/CIndexer.cpp

 #ifdef __CYGWIN__
 #include <cygwin/version.h>
 #include <sys/cygwin.h>
 #define _WIN32 1
 #endif
 
 #ifdef _WIN32
 #include <windows.h>
+#elif defined(_AIX)
+#include <errno.h>
+#include <sys/ldr.h>
 #else
 #include <dlfcn.h>
 #endif
 
 using namespace clang;
 
+#ifdef _AIX
+namespace clang {
+namespace {
+
+template <typename LibClangPathType>
+void getClangResourcesPathImplAIX(LibClangPathType &LibClangPath) {
+  int PrevErrno = errno;
+
+  size_t BufSize = 2048u;
+  std::unique_ptr<char[]> Buf;
+  while (true) {
+    Buf = llvm::make_unique<char []>(BufSize);
+    errno = 0;
+    int Ret = loadquery(L_GETXINFO, Buf.get(), (unsigned int)BufSize);
+    if (Ret != -1)
+      break; // loadquery() was successful.
+    if (errno != ENOMEM)
+      llvm_unreachable("Encountered an unexpected loadquery() failure");
+
+    // errno == ENOMEM; try to allocate more memory.
+    if ((BufSize & ~((-1u) >> 1u)) != 0u)
+      llvm::report_fatal_error("BufSize needed for loadquery() too large");
+
+    Buf.release();
+    BufSize <<= 1u;
+  }
+
+  // Extract the function entry point from the function descriptor.
+  uint64_t EntryAddr =
+      reinterpret_cast<uintptr_t &>(clang_createTranslationUnit);
+
+  // Loop to locate the function entry point in the loadquery() results.
+  ld_xinfo *CurInfo = reinterpret_cast<ld_xinfo *>(Buf.get());
+  while (true) {
+    uint64_t CurTextStart = (uint64_t)CurInfo->ldinfo_textorg;
+    uint64_t CurTextEnd = CurTextStart + CurInfo->ldinfo_textsize;
+    if (CurTextStart <= EntryAddr && EntryAddr < CurTextEnd)
+      break; // Successfully located.
+
+    if (CurInfo->ldinfo_next == 0u)
+      llvm::report_fatal_error("Cannot locate entry point in "
+                               "the loadquery() results");
+    CurInfo = reinterpret_cast<ld_xinfo *>(reinterpret_cast<char *>(CurInfo) +
+                                           CurInfo->ldinfo_next);
+  }
+
+  LibClangPath += reinterpret_cast<char *>(CurInfo) + CurInfo->ldinfo_filename;
+  errno = PrevErrno;
+}
+
+} // end anonymous namespace
+} // end namespace clang
+#endif
+
 const std::string &CIndexer::getClangResourcesPath() {
   // Did we already compute the path?
   if (!ResourcesPath.empty())
     return ResourcesPath;
 
   SmallString<128> LibClangPath;
 
   // Find the location where this library lives (libclang.dylib).

 #if CYGWIN_VERSION_API_MAJOR > 0 || CYGWIN_VERSION_API_MINOR >= 181
   cygwin_conv_path(CCP_WIN_A_TO_POSIX, w32path, path, MAX_PATH);
 #else
   cygwin_conv_to_full_posix_path(w32path, path);
 #endif
 #endif
 
   LibClangPath += path;
+#elif defined(_AIX)
+  getClangResourcesPathImplAIX(LibClangPath);
 #else
   // This silly cast below avoids a C++ warning.
   Dl_info info;
   if (dladdr((void *)(uintptr_t)clang_createTranslationUnit, &info) == 0)
     llvm_unreachable("Call to dladdr() failed");
 
   // We now have the CIndex directory, locate clang relative to it.
   LibClangPath += info.dli_fname;