Fix a crash that occurs when PWD is invalid.

MCJIT needs to be able to run in hostile environments, even when PWD
is invalid. There's no need to crash MCJIT in this case.

The obvious fix is to simply leave MCContext's CompilationDir empty
when PWD can't be determined. This way, MCJIT clients,
and other clients that link with LLVM don’t need a valid working directory.

If we do want to guarantee valid CompilationDir, that should be done
only for clients of getCompilationDir(). This is as simple as checking
for an empty string.

The only current use of getCompilationDir is EmitGenDwarfInfo, which
won’t conceivably run with an invalid working dir. However, in the
purely hypothetically and untestable case that this happens, the
AT_comp_dir will be omitted from the compilation_unit DIE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196874 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/MC/MCContext.h b/include/llvm/MC/MCContext.h
index c8b66261bfea7458f7e7e0a477521212d74ebef6..17a37ed3b9d7f138ec68adadb768e81d828e22e8 100644 (file)
--- a/include/llvm/MC/MCContext.h
+++ b/include/llvm/MC/MCContext.h
@@ -278,6 +278,7 @@ namespace llvm {
     /// This can be overridden by clients which want to control the reported
     /// compilation directory and have it be something other than the current
     /// working directory.
+    /// Returns an empty string if the current directory cannot be determined.
     StringRef getCompilationDir() const { return CompilationDir; }
 
     /// \brief Set the compilation directory for DW_AT_comp_dir

diff --git a/lib/MC/MCContext.cpp b/lib/MC/MCContext.cpp
index bd5793cbb9f0836d718115056a1fa9ffd117dda1..42056c951ca5b2b93a1d5392343903b72ddae1f6 100644 (file)
--- a/lib/MC/MCContext.cpp
+++ b/lib/MC/MCContext.cpp
@@ -47,8 +47,8 @@ MCContext::MCContext(const MCAsmInfo *mai, const MCRegisterInfo *mri,
   AllowTemporaryLabels(true), DwarfCompileUnitID(0), AutoReset(DoAutoReset) {
 
   error_code EC = llvm::sys::fs::current_path(CompilationDir);
-  assert(!EC && "Could not determine the current directory");
-  (void)EC;
+  if (EC)
+    CompilationDir.clear();
 
   MachOUniquingMap = 0;
   ELFUniquingMap = 0;

diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 1e5c2e34c488bf231b2dd4b2a51cf092a3aae8b1..479f4452d4a3b501c065540265dc449b048cf540 100644 (file)
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -467,7 +467,8 @@ static void EmitGenDwarfAbbrev(MCStreamer *MCOS) {
   EmitAbbrev(MCOS, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr);
   EmitAbbrev(MCOS, dwarf::DW_AT_high_pc, dwarf::DW_FORM_addr);
   EmitAbbrev(MCOS, dwarf::DW_AT_name, dwarf::DW_FORM_string);
-  EmitAbbrev(MCOS, dwarf::DW_AT_comp_dir, dwarf::DW_FORM_string);
+  if (!context.getCompilationDir().empty())
+    EmitAbbrev(MCOS, dwarf::DW_AT_comp_dir, dwarf::DW_FORM_string);
   StringRef DwarfDebugFlags = context.getDwarfDebugFlags();
   if (!DwarfDebugFlags.empty())
     EmitAbbrev(MCOS, dwarf::DW_AT_APPLE_flags, dwarf::DW_FORM_string);
@@ -643,8 +644,10 @@ static void EmitGenDwarfInfo(MCStreamer *MCOS,
   MCOS->EmitIntValue(0, 1); // NULL byte to terminate the string.
 
   // AT_comp_dir, the working directory the assembly was done in.
-  MCOS->EmitBytes(context.getCompilationDir());
-  MCOS->EmitIntValue(0, 1); // NULL byte to terminate the string.
+  if (!context.getCompilationDir().empty()) {
+    MCOS->EmitBytes(context.getCompilationDir());
+    MCOS->EmitIntValue(0, 1); // NULL byte to terminate the string.
+  }
 
   // AT_APPLE_flags, the command line arguments of the assembler tool.
   StringRef DwarfDebugFlags = context.getDwarfDebugFlags();