[llvm] r354319 - [yaml2obj] - Do not skip zeroes blocks if there are relocations against them.

[George Rimar via llvm-commits]

Author: grimar
Date: Tue Feb 19 04:38:36 2019
New Revision: 354319

URL: http://llvm.org/viewvc/llvm-project?rev=354319&view=rev
Log:
[yaml2obj] - Do not skip zeroes blocks if there are relocations against them.

This is for -D -reloc combination.

With this patch, we do not skip the zero bytes that have a relocation against
them when -reloc is used. If -reloc is not used, then the behavior will be the same.

Differential revision: https://reviews.llvm.org/D58174

Added:
    llvm/trunk/test/tools/llvm-objdump/disasm-zeroes-relocations.test
Modified:
    llvm/trunk/tools/llvm-objdump/llvm-objdump.cpp

Added: llvm/trunk/test/tools/llvm-objdump/disasm-zeroes-relocations.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-objdump/disasm-zeroes-relocations.test?rev=354319&view=auto
==============================================================================
--- llvm/trunk/test/tools/llvm-objdump/disasm-zeroes-relocations.test (added)
+++ llvm/trunk/test/tools/llvm-objdump/disasm-zeroes-relocations.test Tue Feb 19 04:38:36 2019
@@ -0,0 +1,52 @@
+# RUN: yaml2obj %s > %t
+
+## Check we do not skip zeroes blocks if have relocations pointed to these places.
+# RUN: llvm-objdump -D -reloc %t
+
+# CHECK:      Disassembly of section .rodata:
+# CHECK-NEXT: 0000000000000000 .rodata:
+# CHECK-NEXT:        0:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:                 0000000000000000:  R_X86_64_64  *ABS*
+# CHECK-NEXT:        2:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:        4:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:        6:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:        8:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:                 0000000000000008:  R_X86_64_64  *ABS*
+# CHECK-NEXT:        a:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:        c:       00 00   addb    %al, (%rax)
+# CHECK-NEXT:        e:       00 00   addb    %al, (%rax)
+
+## Check that without -reloc all zeroes would be omitted.
+# RUN: llvm-objdump -D %t | FileCheck %s --check-prefix=SKIP
+
+# SKIP:      Disassembly of section .rodata:
+# SKIP-NEXT: 0000000000000000 .rodata:
+# SKIP-NEXT:   ...
+# SKIP-NEXT: Disassembly of section .rela.rodata:
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .rodata
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x0000000000000001
+    Content:         '00000000000000000000000000000000'
+  - Name:            .rela.rodata
+    Type:            SHT_RELA
+    Flags:           [ SHF_INFO_LINK ]
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    EntSize:         0x0000000000000018
+    Info:            .rodata
+    Relocations:
+      - Offset:          0x0000000000000000
+        Symbol:          x
+        Type:            R_X86_64_64
+      - Offset:          0x0000000000000008
+        Symbol:          x
+        Type:            R_X86_64_64

Modified: llvm/trunk/tools/llvm-objdump/llvm-objdump.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objdump/llvm-objdump.cpp?rev=354319&r1=354318&r2=354319&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objdump/llvm-objdump.cpp (original)
+++ llvm/trunk/tools/llvm-objdump/llvm-objdump.cpp Tue Feb 19 04:38:36 2019
@@ -863,10 +863,6 @@ static void addPltEntries(const ObjectFi
 // returns the number of zero bytes that can be skipped when dumping the
 // disassembly of the instructions in Buf.
 static size_t countSkippableZeroBytes(ArrayRef<uint8_t> Buf) {
-  // When -z or --disassemble-zeroes are given we always dissasemble them.
-  if (DisassembleZeroes)
-    return 0;
-
   // Find the number of leading zeroes.
   size_t N = 0;
   while (N < Buf.size() && !Buf[N])
@@ -1284,12 +1280,22 @@ static void disassembleObject(const Targ
         if (Index >= End)
           break;
 
-        if (size_t N =
-                countSkippableZeroBytes(Bytes.slice(Index, End - Index))) {
-          outs() << "\t\t..." << '\n';
-          Index += N;
-          if (Index >= End)
-            break;
+        // When -z or --disassemble-zeroes are given we always dissasemble them.
+        // Otherwise we might want to skip zero bytes we see.
+        if (!DisassembleZeroes) {
+          uint64_t MaxOffset = End - Index;
+          // For -reloc: print zero blocks patched by relocations, so that
+          // relocations can be shown in the dump.
+          if (RelCur != RelEnd)
+            MaxOffset = RelCur->getOffset() - Index;
+
+          if (size_t N =
+                  countSkippableZeroBytes(Bytes.slice(Index, MaxOffset))) {
+            outs() << "\t\t..." << '\n';
+            Index += N;
+            if (Index >= End)
+              break;
+          }
         }
 
         // Disassemble a real instruction or a data when disassemble all is