From 549758f5225a941f7e1e4fac72fd205152c5ab1d Mon Sep 17 00:00:00 2001
From: Dmitry Preobrazhensky <dmitry.preobrazhensky@amd.com>
Date: Mon, 18 May 2020 14:04:58 +0300
Subject: [PATCH] [AMDGPU][MC] Corrected branch relocation handling to detect
 undefined labels

Fixed ELF object writer to die gracefully when an undefined label is encountered in a branch instruction.
See https://bugs.llvm.org/show_bug.cgi?id=41914.

Reviewers: arsenm, rampitec

Differential Revision: https://reviews.llvm.org/D79943
---
 .../AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp     | 11 +++++++++++
 test/MC/AMDGPU/labels-branch-err.s                    |  4 ++++
 2 files changed, 15 insertions(+)
 create mode 100644 test/MC/AMDGPU/labels-branch-err.s

diff --git a/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp b/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp
index d352219a7a9..619fde74e88 100644
--- a/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp
+++ b/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp
@@ -6,8 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "AMDGPUFixupKinds.h"
 #include "AMDGPUMCTargetDesc.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCELFObjectWriter.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCFixup.h"
@@ -80,6 +82,15 @@ unsigned AMDGPUELFObjectWriter::getRelocType(MCContext &Ctx,
     return ELF::R_AMDGPU_ABS64;
   }
 
+  if (Fixup.getTargetKind() == AMDGPU::fixup_si_sopp_br) {
+    const auto *SymA = Target.getSymA();
+    assert(SymA);
+
+    Ctx.reportError(Fixup.getLoc(),
+                    Twine("undefined label '") + SymA->getSymbol().getName() + "'");
+    return ELF::R_AMDGPU_NONE;
+  }
+
   llvm_unreachable("unhandled relocation type");
 }
 
diff --git a/test/MC/AMDGPU/labels-branch-err.s b/test/MC/AMDGPU/labels-branch-err.s
new file mode 100644
index 00000000000..e7e8bd114a9
--- /dev/null
+++ b/test/MC/AMDGPU/labels-branch-err.s
@@ -0,0 +1,4 @@
+//  RUN: not llvm-mc -arch=amdgcn -filetype=obj -o /dev/null %s 2>&1 | FileCheck -check-prefix=ERROR %s
+//  ERROR: error: undefined label 'undef_label'
+
+s_branch undef_label