[SystemZ][z/OS] Add z/OS customization file (llvm#111182)

On z/OS, the location of the system libraries and side decks (aka
equivalent to libc, etc) are not in a predefined location. The system
does have a default location but sysadmins can change this and
frequently do. See the -mzos-hlq* options we have for z/OS.

To avoid every user needing to specify these -mzos-hlq* options, we
added support for a system install default config file that is always
read independent of the usual config file. The compiler will read this
customization config file before reading the usual config files.

The customization file is called clang.cfg and is located in:
- the etc dir within the compiler installation dir.
- or specified by the CLANG_CONFIG_PATH env var. This env var can either
be a directory or the fill path name of the file.

clang/include/clang/Driver/Driver.h

@@ -741,6 +741,11 @@ class Driver {
   /// \returns true if error occurred.
   bool loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx);
 
+  /// Tries to load options from customization file.
+  ///
+  /// \returns true if error occurred.
+  bool loadZOSCustomizationFile(llvm::cl::ExpansionContext &);
+
   /// Read options from the specified file.
   ///
   /// \param [in] FileName File to read.

clang/lib/Driver/Driver.cpp

@@ -1063,6 +1063,34 @@ void Driver::CreateOffloadingDeviceToolChains(Compilation &C,
   //
 }
 
+bool Driver::loadZOSCustomizationFile(llvm::cl::ExpansionContext &ExpCtx) {
+  if (IsCLMode() || IsDXCMode() || IsFlangMode())
+    return false;
+
+  SmallString<128> CustomizationFile;
+  StringRef PathLIBEnv = StringRef(getenv("CLANG_CONFIG_PATH")).trim();
+  // If the env var is a directory then append "/clang.cfg" and treat
+  // that as the config file.  Otherwise treat the env var as the
+  // config file.
+  if (!PathLIBEnv.empty()) {
+    llvm::sys::path::append(CustomizationFile, PathLIBEnv);
+    if (llvm::sys::fs::is_directory(PathLIBEnv))
+      llvm::sys::path::append(CustomizationFile, "/clang.cfg");
+    if (llvm::sys::fs::is_regular_file(CustomizationFile))
+      return readConfigFile(CustomizationFile, ExpCtx);
+    Diag(diag::err_drv_config_file_not_found) << CustomizationFile;
+    return true;
+  }
+
+  SmallString<128> BaseDir(llvm::sys::path::parent_path(Dir));
+  llvm::sys::path::append(CustomizationFile, BaseDir + "/etc/clang.cfg");
+  if (llvm::sys::fs::is_regular_file(CustomizationFile))
+    return readConfigFile(CustomizationFile, ExpCtx);
+
+  // If no customization file, just return
+  return false;
+}
+
 static void appendOneArg(InputArgList &Args, const Arg *Opt) {
   // The args for config files or /clang: flags belong to different InputArgList
   // objects than Args. This copies an Arg from one of those other InputArgLists
@@ -1284,11 +1312,18 @@ bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
   }
 
   // Otherwise, use the real triple as used by the driver.
+  llvm::Triple RealTriple =
+      computeTargetTriple(*this, TargetTriple, *CLOptions);
   if (Triple.str().empty()) {
-    Triple = computeTargetTriple(*this, TargetTriple, *CLOptions);
+    Triple = RealTriple;
     assert(!Triple.str().empty());
   }
 
+  // On z/OS, start by loading the customization file before loading
+  // the usual default config file(s).
+  if (RealTriple.isOSzOS() && loadZOSCustomizationFile(ExpCtx))
+    return true;
+
   // Search for config files in the following order:
   // 1. <triple>-<mode>.cfg using real driver mode
   //    (e.g. i386-pc-linux-gnu-clang++.cfg).

clang/test/Driver/Inputs/config-zos/clang.cfg

@@ -0,0 +1 @@
+-DABC=123

clang/test/Driver/Inputs/config-zos/def.cfg

@@ -0,0 +1 @@
+-DDEF=456

clang/test/Driver/Inputs/config-zos/tst/def.cfg

@@ -0,0 +1 @@
+-DDEF=456

clang/test/Driver/config-zos.c

@@ -0,0 +1,17 @@
+// REQUIRES: shell
+// REQUIRES: systemz-registered-target
+
+// RUN: unset CLANG_NO_DEFAULT_CONFIG
+// RUN: rm -rf %t && mkdir %t
+
+// RUN: mkdir -p %t/testbin
+// RUN: mkdir -p %t/etc
+// RUN: ln -s %clang %t/testbin/clang
+// RUN: echo "-DXYZ=789" >%t/etc/clang.cfg
+// RUN: %t/testbin/clang --target=s390x-ibm-zos -c -### -no-canonical-prefixes %s 2>&1 | FileCheck -DDIR=%t %s 
+// RUN: %t/testbin/clang --target=s390x-ibm-zos -c -### -no-canonical-prefixes --no-default-config %s 2>&1 | FileCheck -check-prefix=NOCONFIG %s 
+//
+// CHECK: Configuration file: [[DIR]]/etc/clang.cfg
+// CHECK: "-D" "XYZ=789"
+// NOCONFIG-NOT: Configuration file: {{.*}}/etc/clang.cfg
+// NOCONFIG-NOT: "-D" "XYZ=789"

clang/test/Driver/config-zos1.c

@@ -0,0 +1,23 @@
+// REQUIRES: shell
+// REQUIRES: systemz-registered-target
+
+// RUN: unset CLANG_NO_DEFAULT_CONFIG
+
+// RUN: export CLANG_CONFIG_PATH=%S/Inputs/config-zos
+// RUN: %clang --target=s390x-ibm-zos -c -### %s 2>&1 | FileCheck %s 
+// CHECK: Configuration file: {{.*}}/Inputs/config-zos/clang.cfg
+// CHECK: "-D" "ABC=123"
+
+// RUN: export CLANG_CONFIG_PATH=%S/Inputs/config-zos/def.cfg
+// RUN: %clang --target=s390x-ibm-zos -c -### %s 2>&1 | FileCheck %s -check-prefix=CHECK-DEF
+// CHECK-DEF: Configuration file: {{.*}}/Inputs/config-zos/def.cfg
+// CHECK-DEF: "-D" "DEF=456"
+
+// RUN: export CLANG_CONFIG_PATH=%S/Inputs/config-zos/Garbage
+// RUN: not %clang --target=s390x-ibm-zos -c -### %s 2>&1 | FileCheck %s  -check-prefix=CHECK-ERR
+// CHECK-ERR:  error: configuration file '{{.*}}/Inputs/config-zos/Garbage' cannot be found
+
+// The directory exists but no clang.cfg in it
+// RUN: export CLANG_CONFIG_PATH=%S/Inputs/config-zos/tst
+// RUN: not %clang --target=s390x-ibm-zos -c -### %s 2>&1 | FileCheck %s  -check-prefix=CHECK-ERRDIR
+// CHECK-ERRDIR:  error: configuration file '{{.*}}/Inputs/config-zos/tst/clang.cfg' cannot be found