From 64f4a52b527244bafe5f469ee5f557c7fa6635c0 Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks@fb.com>
Date: Tue, 31 Aug 2021 11:53:54 -0700
Subject: [PATCH] [llvm-objdump] Fix 'llvm-objdump -dr' for executables with
 relocations

Print relocations interleaved with disassembled instructions for
executables with relocatable sections, e.g. those built with "-Wl,-q".

Differential Revision: https://reviews.llvm.org/D109016

(cherry picked from commit 6300e4ac5806c9255c68c6fada37b2ce70efc524)
---
 .../X86/elf-disassemble-relocs-exec.test      | 59 +++++++++++++++++++
 tools/llvm-objdump/llvm-objdump.cpp           |  9 ++-
 2 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 test/tools/llvm-objdump/X86/elf-disassemble-relocs-exec.test

diff --git a/test/tools/llvm-objdump/X86/elf-disassemble-relocs-exec.test b/test/tools/llvm-objdump/X86/elf-disassemble-relocs-exec.test
new file mode 100644
index 00000000000..16216c68e1b
--- /dev/null
+++ b/test/tools/llvm-objdump/X86/elf-disassemble-relocs-exec.test
@@ -0,0 +1,59 @@
+## Check that 'llvm-objdump -dr' correctly prints relocations in executables.
+
+# RUN: yaml2obj --docnum=1 %s -o %t
+# RUN: llvm-objdump -dr %t | FileCheck %s
+
+# CHECK:       400000: 90                            nop
+# CHECK-NEXT:  400001: bf 10 00 40 00                movl    $4194320, %edi
+# CHECK-NEXT:                0000000000400002:  R_X86_64_32  .rodata
+# CHECK-NEXT:  400006: e8 fc fe ff ff                callq   0x3fff07
+# CHECK-NEXT:                0000000000400007:  R_X86_64_PLT32       puts-0x4
+# CHECK-NEXT:  40000b: 90                            nop
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_X86_64
+ProgramHeaders:
+  - Type:            PT_LOAD
+    Flags:           [ PF_X, PF_R ]
+    FirstSec:        .text
+    LastSec:         .rodata
+    VAddr:           0x400000
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x400000
+    AddressAlign:    0x10
+    Content:         90BF10004000E8FCFEFFFF90
+  - Name:            .rodata
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x8
+    Content:         00
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Flags:           [ SHF_INFO_LINK ]
+    AddressAlign:    0x8
+    Info:            .text
+    Relocations:
+      - Offset:          0x400002
+        Symbol:          .rodata
+        Type:            R_X86_64_32
+        Addend:          0
+      - Offset:          0x400007
+        Symbol:          puts
+        Type:            R_X86_64_PLT32
+        Addend:          -4
+Symbols:
+  - Name:            .rodata
+    Type:            STT_SECTION
+    Section:         .rodata
+    Value:           0x400628
+  - Name:            puts
+    Type:            STT_FUNC
+    Binding:         STB_GLOBAL
+...
diff --git a/tools/llvm-objdump/llvm-objdump.cpp b/tools/llvm-objdump/llvm-objdump.cpp
index 48ae92f734c..9d461b08f3f 100644
--- a/tools/llvm-objdump/llvm-objdump.cpp
+++ b/tools/llvm-objdump/llvm-objdump.cpp
@@ -1286,6 +1286,10 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile *Obj,
     if (shouldAdjustVA(Section))
       VMAAdjustment = AdjustVMA;
 
+    // In executable and shared objects, r_offset holds a virtual address.
+    // Subtract SectionAddr from the r_offset field of a relocation to get
+    // the section offset.
+    uint64_t RelAdjustment = Obj->isRelocatableObject() ? 0 : SectionAddr;
     uint64_t Size;
     uint64_t Index;
     bool PrintedSection = false;
@@ -1432,7 +1436,8 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile *Obj,
             // For --reloc: print zero blocks patched by relocations, so that
             // relocations can be shown in the dump.
             if (RelCur != RelEnd)
-              MaxOffset = RelCur->getOffset() - Index;
+              MaxOffset = std::min(RelCur->getOffset() - RelAdjustment - Index,
+                                   MaxOffset);
 
             if (size_t N =
                     countSkippableZeroBytes(Bytes.slice(Index, MaxOffset))) {
@@ -1581,7 +1586,7 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile *Obj,
         if (Obj->getArch() != Triple::hexagon) {
           // Print relocation for instruction and data.
           while (RelCur != RelEnd) {
-            uint64_t Offset = RelCur->getOffset();
+            uint64_t Offset = RelCur->getOffset() - RelAdjustment;
             // If this relocation is hidden, skip it.
             if (getHidden(*RelCur) || SectionAddr + Offset < StartAddress) {
               ++RelCur;