[Clang][Driver] Expose relocation model as multilib flags (#149132)

If a multilib collection contains libraries built for different methods
of accessing global data (via absolute address, or via a GOT in -fPIC
style, or as an offset from a fixed register in Arm -frwpi style), then
`multilib.yaml` will need to know which relocation model an application
is using in order to select the right library.

Even if a multilib collection only supports one relocation model, it's
still useful for `multilib.yaml` to be able to tell if the user has
selected the right one, so as to give a useful error message if they
haven't, instead of silently selecting a library that won't work.

In this commit we determine the PIC / ROPI / RWPI status using the
existing logic in `ParsePICArgs`, and translate it back into a canonical
set of multilib selection flags.

Author: statham-arm

clang/lib/Driver/ToolChain.cpp

@@ -258,10 +258,10 @@ static void getAArch64MultilibFlags(const Driver &D,
   processMultilibCustomFlags(Result, Args);
 }
 
-static void getARMMultilibFlags(const Driver &D,
-                                      const llvm::Triple &Triple,
-                                      const llvm::opt::ArgList &Args,
-                                      Multilib::flags_list &Result) {
+static void getARMMultilibFlags(const Driver &D, const llvm::Triple &Triple,
+                                llvm::Reloc::Model RelocationModel,
+                                const llvm::opt::ArgList &Args,
+                                Multilib::flags_list &Result) {
   std::vector<StringRef> Features;
   llvm::ARM::FPUKind FPUKind = tools::arm::getARMTargetFeatures(
       D, Triple, Args, Features, false /*ForAs*/, true /*ForMultilib*/);
@@ -304,6 +304,18 @@ static void getARMMultilibFlags(const Driver &D,
     llvm_unreachable("Invalid float ABI");
   }
 
+  if (RelocationModel == llvm::Reloc::ROPI ||
+      RelocationModel == llvm::Reloc::ROPI_RWPI)
+    Result.push_back("-fropi");
+  else
+    Result.push_back("-fno-ropi");
+
+  if (RelocationModel == llvm::Reloc::RWPI ||
+      RelocationModel == llvm::Reloc::ROPI_RWPI)
+    Result.push_back("-frwpi");
+  else
+    Result.push_back("-fno-rwpi");
+
   const Arg *BranchProtectionArg =
       Args.getLastArgNoClaim(options::OPT_mbranch_protection_EQ);
   if (BranchProtectionArg) {
@@ -344,6 +356,18 @@ ToolChain::getMultilibFlags(const llvm::opt::ArgList &Args) const {
   const llvm::Triple Triple(ComputeEffectiveClangTriple(Args));
   Result.push_back("--target=" + Triple.str());
 
+  // A difference of relocation model (absolutely addressed data, PIC, Arm
+  // ROPI/RWPI) is likely to change whether a particular multilib variant is
+  // compatible with a given link. Determine the relocation model of the
+  // current link, so as to add appropriate multilib flags.
+  llvm::Reloc::Model RelocationModel;
+  unsigned PICLevel;
+  bool IsPIE;
+  {
+    RegisterEffectiveTriple TripleRAII(*this, Triple);
+    std::tie(RelocationModel, PICLevel, IsPIE) = ParsePICArgs(*this, Args);
+  }
+
   switch (Triple.getArch()) {
   case llvm::Triple::aarch64:
   case llvm::Triple::aarch64_32:
@@ -354,7 +378,7 @@ ToolChain::getMultilibFlags(const llvm::opt::ArgList &Args) const {
   case llvm::Triple::armeb:
   case llvm::Triple::thumb:
   case llvm::Triple::thumbeb:
-    getARMMultilibFlags(D, Triple, Args, Result);
+    getARMMultilibFlags(D, Triple, RelocationModel, Args, Result);
     break;
   case llvm::Triple::riscv32:
   case llvm::Triple::riscv64:
@@ -376,6 +400,12 @@ ToolChain::getMultilibFlags(const llvm::opt::ArgList &Args) const {
   else
     Result.push_back("-fexceptions");
 
+  if (RelocationModel == llvm::Reloc::PIC_)
+    Result.push_back(IsPIE ? (PICLevel > 1 ? "-fPIE" : "-fpie")
+                           : (PICLevel > 1 ? "-fPIC" : "-fpic"));
+  else
+    Result.push_back("-fno-pic");
+
   // Sort and remove duplicates.
   std::sort(Result.begin(), Result.end());
   Result.erase(llvm::unique(Result), Result.end());

clang/test/Driver/print-multi-selection-flags.c

@@ -107,3 +107,22 @@
 // CHECK-AARCH64-MULTILIB-CUSTOM-FLAG: --target=aarch64-unknown-none-eabi
 // CHECK-MULTILIB-CUSTOM-FLAG-DAG:     -fmultilib-flag=foo
 // CHECK-MULTILIB-CUSTOM-FLAG-DAG:     -fmultilib-flag=bar
+
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fropi              | FileCheck --check-prefixes=CHECK-ROPI,CHECK-NO-RWPI,CHECK-NO-PIC %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -frwpi              | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-RWPI,CHECK-NO-PIC %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fropi -frwpi       | FileCheck --check-prefixes=CHECK-ROPI,CHECK-RWPI,CHECK-NO-PIC %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fno-ropi -fno-rwpi | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-NO-PIC %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a                     | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-NO-PIC %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fpic               | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIC1 %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fPIC               | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIC2 %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fpie               | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIE1 %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fPIE               | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIE2 %s
+// CHECK-PIC2: -fPIC
+// CHECK-PIE2: -fPIE
+// CHECK-NO-PIC: -fno-pic
+// CHECK-NO-ROPI: -fno-ropi
+// CHECK-NO-RWPI: -fno-rwpi
+// CHECK-PIC1: -fpic
+// CHECK-PIE1: -fpie
+// CHECK-ROPI: -fropi
+// CHECK-RWPI: -frwpi