Add support for x32-abi

Detect x32-abi through CMakeCompilerABI infrastruture and use this
information at runtime to determine the correct library paths with
`FIND_LIBRARY_USE_LIBX32_PATHS`.

Fixes: #15994

Source/cmExportInstallFileGenerator.cxx

@@ -195,8 +195,10 @@ void cmExportInstallFileGenerator::GenerateImportPrefix(std::ostream& os)
        << " \"${CMAKE_CURRENT_LIST_FILE}\" PATH)\n";
     if (cmHasLiteralPrefix(absDestS.c_str(), "/lib/") ||
         cmHasLiteralPrefix(absDestS.c_str(), "/lib64/") ||
+        cmHasLiteralPrefix(absDestS.c_str(), "/libx32/") ||
         cmHasLiteralPrefix(absDestS.c_str(), "/usr/lib/") ||
-        cmHasLiteralPrefix(absDestS.c_str(), "/usr/lib64/")) {
+        cmHasLiteralPrefix(absDestS.c_str(), "/usr/lib64/") ||
+        cmHasLiteralPrefix(absDestS.c_str(), "/usr/libx32/")) {
       // Handle "/usr move" symlinks created by some Linux distros.
       /* clang-format off */
       os <<

Source/cmFindLibraryCommand.cxx

@@ -43,7 +43,8 @@ bool cmFindLibraryCommand::InitialPass(std::vector<std::string> const& argsIn,
     return true;
   }
 
-  // add custom lib<qual> paths instead of using fixed lib32 or lib64
+  // add custom lib<qual> paths instead of using fixed lib32, lib64 or
+  // libx32
   if (const char* customLib = this->Makefile->GetDefinition(
         "CMAKE_FIND_LIBRARY_CUSTOM_LIB_SUFFIX")) {
     this->AddArchitecturePaths(customLib);
@@ -60,6 +61,12 @@ bool cmFindLibraryCommand::InitialPass(std::vector<std::string> const& argsIn,
              "FIND_LIBRARY_USE_LIB64_PATHS")) {
     this->AddArchitecturePaths("64");
   }
+  // add special 32 bit paths if this is an x32 compile.
+  else if (this->Makefile->PlatformIsx32() &&
+           this->Makefile->GetState()->GetGlobalPropertyAsBool(
+             "FIND_LIBRARY_USE_LIBX32_PATHS")) {
+    this->AddArchitecturePaths("x32");
+  }
 
   std::string library = this->FindLibrary();
   if (library != "") {

Source/cmFindPackageCommand.cxx

@@ -92,6 +92,7 @@ cmFindPackageCommand::cmFindPackageCommand()
   this->DebugMode = false;
   this->UseLib32Paths = false;
   this->UseLib64Paths = false;
+  this->UseLibx32Paths = false;
   this->PolicyScope = true;
   this->VersionMajor = 0;
   this->VersionMinor = 0;
@@ -173,6 +174,13 @@ bool cmFindPackageCommand::InitialPass(std::vector<std::string> const& args,
     this->UseLib64Paths = true;
   }
 
+  // Lookup whether libx32 paths should be used.
+  if (this->Makefile->PlatformIsx32() &&
+      this->Makefile->GetState()->GetGlobalPropertyAsBool(
+        "FIND_LIBRARY_USE_LIBX32_PATHS")) {
+    this->UseLibx32Paths = true;
+  }
+
   // Check if User Package Registry should be disabled
   if (this->Makefile->IsOn("CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY")) {
     this->NoUserRegistry = true;
@@ -2002,6 +2010,9 @@ bool cmFindPackageCommand::SearchPrefix(std::string const& prefix_in)
   if (this->UseLib64Paths) {
     common.push_back("lib64");
   }
+  if (this->UseLibx32Paths) {
+    common.push_back("libx32");
+  }
   common.push_back("lib");
   common.push_back("share");
 

Source/cmFindPackageCommand.h

@@ -169,6 +169,7 @@ private:
   bool DebugMode;
   bool UseLib32Paths;
   bool UseLib64Paths;
+  bool UseLibx32Paths;
   bool PolicyScope;
   std::string LibraryArchitecture;
   std::vector<std::string> Names;

Source/cmMakefile.cxx

@@ -2149,6 +2149,12 @@ bool cmMakefile::IsSet(const std::string& name) const
 
 bool cmMakefile::PlatformIs32Bit() const
 {
+  if (const char* plat_abi =
+        this->GetDefinition("CMAKE_INTERNAL_PLATFORM_ABI")) {
+    if (strcmp(plat_abi, "ELF X32") == 0) {
+      return false;
+    }
+  }
   if (const char* sizeof_dptr = this->GetDefinition("CMAKE_SIZEOF_VOID_P")) {
     return atoi(sizeof_dptr) == 4;
   }
@@ -2163,6 +2169,17 @@ bool cmMakefile::PlatformIs64Bit() const
   return false;
 }
 
+bool cmMakefile::PlatformIsx32() const
+{
+  if (const char* plat_abi =
+        this->GetDefinition("CMAKE_INTERNAL_PLATFORM_ABI")) {
+    if (strcmp(plat_abi, "ELF X32") == 0) {
+      return true;
+    }
+  }
+  return false;
+}
+
 bool cmMakefile::PlatformIsAppleIos() const
 {
   std::string sdkRoot;

Source/cmMakefile.h

@@ -436,6 +436,8 @@ public:
 
   /** Return whether the target platform is 64-bit.  */
   bool PlatformIs64Bit() const;
+  /** Return whether the target platform is x32.  */
+  bool PlatformIsx32() const;
 
   /** Return whether the target platform is Apple iOS.  */
   bool PlatformIsAppleIos() const;