[BPF] Generate BTF DebugInfo under BPF target

This patch implements BTF (BPF Type Format).
The BTF is the debug info format for BPF, introduced
in the below linux patch:
  https://github.com/torvalds/linux/commit/69b693f0aefa0ed521e8bd02260523b5ae446ad7#diff-06fb1c8825f653d7e539058b72c83332
and further extended several times, e.g.,
  https://www.spinics.net/lists/netdev/msg534640.html
  https://www.spinics.net/lists/netdev/msg538464.html
  https://www.spinics.net/lists/netdev/msg540246.html

The main advantage of implementing in LLVM is:
   . better integration/deployment as no extra tools are needed.
   . bpf JIT based compilation (like bcc, bpftrace, etc.) can get
     BTF without much extra effort.
   . BTF line_info needs selective source codes, which can be
     easily retrieved when inside the compiler.

This patch implemented BTF generation by registering a BPF
specific DebugHandler in BPFAsmPrinter.

Signed-off-by: Yonghong Song <yhs@fb.com>

Differential Revision: https://reviews.llvm.org/D55752

llvm-svn: 349640

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Target/BPF/BPFAsmPrinter.cpp b/llvm/lib/Target/BPF/BPFAsmPrinter.cpp
index 705211b486b..ada5eb923f4 100644
--- a/llvm/lib/Target/BPF/BPFAsmPrinter.cpp
+++ b/llvm/lib/Target/BPF/BPFAsmPrinter.cpp
@@ -16,6 +16,7 @@
 #include "BPFInstrInfo.h"
 #include "BPFMCInstLower.h"
 #include "BPFTargetMachine.h"
+#include "BTFDebug.h"
 #include "InstPrinter/BPFInstPrinter.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
@@ -40,6 +41,7 @@ public:
       : AsmPrinter(TM, std::move(Streamer)) {}
 
   StringRef getPassName() const override { return "BPF Assembly Printer"; }
+  bool doInitialization(Module &M) override;
   void printOperand(const MachineInstr *MI, int OpNum, raw_ostream &O);
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
@@ -52,6 +54,18 @@ public:
 };
 } // namespace
 
+bool BPFAsmPrinter::doInitialization(Module &M) {
+  AsmPrinter::doInitialization(M);
+
+  if (MAI->doesSupportDebugInformation()) {
+    Handlers.push_back(HandlerInfo(new BTFDebug(this), "emit",
+                                   "Debug Info Emission", "BTF",
+                                   "BTF Emission"));
+  }
+
+  return false;
+}
+
 void BPFAsmPrinter::printOperand(const MachineInstr *MI, int OpNum,
                                  raw_ostream &O) {
   const MachineOperand &MO = MI->getOperand(OpNum);