From e15c1079cb4942f8975cf318b5deb87ed31c250a Mon Sep 17 00:00:00 2001
From: Andrew Trick <atrick@apple.com>
Date: Tue, 10 Dec 2013 04:39:09 +0000
Subject: [PATCH] Fix a crash that occurs when PWD is invalid.
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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
---
 include/llvm/MC/MCContext.h | 1 +
 lib/MC/MCContext.cpp        | 4 ++--
 lib/MC/MCDwarf.cpp          | 9 ++++++---
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/llvm/MC/MCContext.h b/include/llvm/MC/MCContext.h
index c8b66261bfe..17a37ed3b9d 100644
--- 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 bd5793cbb9f..42056c951ca 100644
--- 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 1e5c2e34c48..479f4452d4a 100644
--- 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();