[PATCH] D77640: [llvm-objdump] Fix unstable disassembly output for sections with same address

[James Henderson via Phabricator via llvm-commits]

jhenderson created this revision.
jhenderson added reviewers: MaskRay, grimar, davidb, thopre.
Herald added a subscriber: rupprecht.
Herald added a project: LLVM.

When two sections shared the same address, the disassembly code was using pointer values to break ties when sorting. Since those values aren't guaranteed to have a specific order, this meant the disassembly code would sometimes change which section to pick when finding symbols targeted by calls in fully linked objects.

This change fixes the non-determinism, so that the same section is always picked. This might have a negative impact in that now a section without any symbol might be picked over a section with symbols, but this will be addressed in a later commit.

Fixes https://bugs.llvm.org/show_bug.cgi?id=45411.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D77640

Files:
  llvm/test/tools/llvm-objdump/X86/disassemble-same-section-addr.test
  llvm/tools/llvm-objdump/llvm-objdump.cpp


Index: llvm/tools/llvm-objdump/llvm-objdump.cpp
===================================================================
--- llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -1228,7 +1228,10 @@
   std::vector<std::pair<uint64_t, SectionRef>> SectionAddresses;
   for (SectionRef Sec : Obj->sections())
     SectionAddresses.emplace_back(Sec.getAddress(), Sec);
-  stable_sort(SectionAddresses);
+  stable_sort(SectionAddresses, [](const std::pair<uint64_t, SectionRef> &LHS,
+                                   const std::pair<uint64_t, SectionRef> &RHS) {
+    return LHS.first < RHS.first;
+  });
 
   // Linked executables (.exe and .dll files) typically don't include a real
   // symbol table but they might contain an export table.
Index: llvm/test/tools/llvm-objdump/X86/disassemble-same-section-addr.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-objdump/X86/disassemble-same-section-addr.test
@@ -0,0 +1,39 @@
+## This test shows that llvm-objdump can handle sections with the same address
+## when symbols in those sections are referenced. In the past, the section
+## picked was non-deterministic, resulting in different symbols being found for
+## the section. The test uses YAML for the input, as we need a fully linked ELF
+## to reproduce the original failure.
+
+# RUN: yaml2obj %s -o %t1 -D SECTION=.second
+# RUN: llvm-objdump -d %t1 | FileCheck %s
+# RUN: yaml2obj %s -o %t2 -D SECTION=.first
+## FIXME: this case should print "<target>" too.
+# RUN: llvm-objdump -d %t2 | FileCheck %s --check-prefix=FAIL
+
+# CHECK: callq 0x5 <target>
+# FAIL:  callq 0x5{{$}}
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:    .caller
+    Type:    SHT_PROGBITS
+    Flags:   [SHF_ALLOC, SHF_EXECINSTR]
+    Address: 0
+    Content: e800000000 # Call instruction to next address.
+  - Name:    .first
+    Type:    SHT_PROGBITS
+    Flags:   [SHF_ALLOC, SHF_EXECINSTR]
+    Address: 5
+  - Name:    .second
+    Type:    SHT_PROGBITS
+    Flags:   [SHF_ALLOC, SHF_EXECINSTR]
+    Address: 5
+Symbols:
+  - Name:    target
+    Section: [[SECTION]]
+    Value:   5


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