[PATCH] D52861: Driver: Prefer gcc toolchains with libgcc_s.so when not static linking libgcc

[Tom Stellard via Phabricator via cfe-commits]

tstellar created this revision.

Fedora ships cross-compilers on all platforms, so a user could end up
with a gcc x86_64 cross-compiler installed on an x86_64 system.  clang
maintains a list of supported triples for each target and when all
else is equal will prefer toolchains with triples that appear earlier
in the list.

The cross-compiler triple on Fedora is x86_64-linux-gnu and this comes
before the Fedora system compiler's triple: x86_64-redhat-linux in
the triples list, so the cross compiler is always preferred.  This
is a problem, because the cross compiler is missing libraries, like
libgcc_s.so, that clang expects to be there so linker invocations
will fail.

This patch fixes this by checking for the existence of libgcc_s.so
when it is required and taking that into account when selecting a
toolchain.


Repository:
  rC Clang

https://reviews.llvm.org/D52861

Files:
  lib/Driver/ToolChains/Gnu.cpp
  lib/Driver/ToolChains/Gnu.h
  test/Driver/Inputs/fedora_28_tree/usr/lib/gcc/x86_64-linux-gnu/7/crtbegin.o
  test/Driver/Inputs/fedora_28_tree/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o
  test/Driver/Inputs/fedora_28_tree/usr/lib/gcc/x86_64-redhat-linux/7/libgcc_s.so
  test/Driver/linux-ld.c


Index: test/Driver/linux-ld.c
===================================================================
--- test/Driver/linux-ld.c
+++ test/Driver/linux-ld.c
@@ -717,6 +717,18 @@
 // CHECK-FEDORA-21-AARCH64: "{{.*}}/usr/lib/gcc/aarch64-redhat-linux/4.9.0{{/|\\\\}}crtend.o"
 // CHECK-FEDORA-21-AARCH64: "{{.*}}/usr/lib/gcc/aarch64-redhat-linux/4.9.0/../../../../lib64{{/|\\\\}}crtn.o"
 //
+// Check that clang does not select the cross compiler by default on Fedora 28.
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=x86_64-unknown-linux-gnu \
+// RUN:     --gcc-toolchain="" \
+// RUN:     --sysroot=%S/Inputs/fedora_28_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-FEDORA-28-X86_64 %s
+//
+// CHECK-FEDORA-28-X86_64: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-FEDORA-28-X86_64: "[[SYSROOT]]/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o"
+// CHECK-FEDORA-28-X86_64: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-redhat-linux/7"
+//
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=arm-unknown-linux-gnueabi \
 // RUN:     --gcc-toolchain="" \
Index: lib/Driver/ToolChains/Gnu.h
===================================================================
--- lib/Driver/ToolChains/Gnu.h
+++ lib/Driver/ToolChains/Gnu.h
@@ -186,6 +186,7 @@
   /// Driver, and has logic for fuzzing that where appropriate.
   class GCCInstallationDetector {
     bool IsValid;
+    bool HasLibGccShared;
     llvm::Triple GCCTriple;
     const Driver &D;
 
@@ -209,7 +210,8 @@
     MultilibSet Multilibs;
 
   public:
-    explicit GCCInstallationDetector(const Driver &D) : IsValid(false), D(D) {}
+    explicit GCCInstallationDetector(const Driver &D)
+        : IsValid(false), HasLibGccShared(false), D(D) {}
     void init(const llvm::Triple &TargetTriple, const llvm::opt::ArgList &Args,
               ArrayRef<std::string> ExtraTripleAliases = None);
 
Index: lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- lib/Driver/ToolChains/Gnu.cpp
+++ lib/Driver/ToolChains/Gnu.cpp
@@ -2199,6 +2199,8 @@
        (TargetArch == llvm::Triple::x86 &&
         TargetTriple.getOS() != llvm::Triple::Solaris)}};
 
+  bool NeedLibgccShared = !Args.hasArg(options::OPT_static_libgcc) &&
+                          !Args.hasArg(options::OPT_static);
   for (auto &Suffix : Suffixes) {
     if (!Suffix.Active)
       continue;
@@ -2216,8 +2218,17 @@
           continue; // Saw this path before; no need to look at it again.
       if (CandidateVersion.isOlderThan(4, 1, 1))
         continue;
-      if (CandidateVersion <= Version)
-        continue;
+
+      bool CandidateHasLibGccShared = false;
+      if (CandidateVersion <= Version) {
+        if (NeedLibgccShared && !HasLibGccShared) {
+          CandidateHasLibGccShared =
+                D.getVFS().exists(LI->path() + "/libgcc_s.so");
+
+        }
+        if (HasLibGccShared || !CandidateHasLibGccShared)
+          continue;
+      }
 
       if (!ScanGCCForMultilibs(TargetTriple, Args, LI->path(),
                                NeedsBiarchSuffix))
@@ -2231,6 +2242,7 @@
       GCCInstallPath = (LibDir + "/" + LibSuffix + "/" + VersionText).str();
       GCCParentLibPath = (GCCInstallPath + "/../" + Suffix.ReversePath).str();
       IsValid = true;
+      HasLibGccShared = CandidateHasLibGccShared;
     }
   }
 }


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