[yaml2obj] - Do not assert when .dynsym is specified explicitly, but .dynstr is not...

We have a code in buildSectionIndex() that adds implicit sections:

// Add special sections after input sections, if necessary.
for (StringRef Name : implicitSectionNames())
  if (SN2I.addName(Name, SecNo)) {
    // Account for this section, since it wasn't in the Doc
    ++SecNo;
    DotShStrtab.add(Name);
  }

The problem arises when .dynsym is specified explicitly and no
DynamicSymbols is used. In that case, we do not add
.dynstr implicitly and will assert later when will try to set Link
for .dynsym.

Seems, in this case, reasonable behavior is to allow Link field to be zero.
This is what this patch does.

Differential revision: https://reviews.llvm.org/D63001

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362929 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/tools/yaml2obj/explicit-dynsym-no-dynstr.yaml b/test/tools/yaml2obj/explicit-dynsym-no-dynstr.yaml
new file mode 100644 (file)
index 0000000..16c4a6a
--- /dev/null
+++ b/test/tools/yaml2obj/explicit-dynsym-no-dynstr.yaml
@@ -0,0 +1,22 @@
+## Check we do not crash/assert when .dynsym is specified
+## explicitly, but .dynstr is not present.
+
+# RUN: yaml2obj %s -o %t
+# RUN: not llvm-readelf --section-headers %t 2>&1 | FileCheck %s
+
+## TODO: Check that .dynsym has Link field set to 0.
+##       GNU readelf is able to dump sections headers,
+##       but llvm-readelf reports an error below too early.
+##       See https://bugs.llvm.org/show_bug.cgi?id=42215.
+
+# CHECK: error: invalid sh_type for string table, expected SHT_STRTAB
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name: .dynsym
+    Type: SHT_SYMTAB

diff --git a/tools/yaml2obj/yaml2elf.cpp b/tools/yaml2obj/yaml2elf.cpp
index be48478..8a53a1b 100644 (file)
--- a/tools/yaml2obj/yaml2elf.cpp
+++ b/tools/yaml2obj/yaml2elf.cpp
@@ -367,7 +367,18 @@ void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
   bool IsStatic = STType == SymtabType::Static;
   SHeader.sh_name = DotShStrtab.getOffset(IsStatic ? ".symtab" : ".dynsym");
   SHeader.sh_type = IsStatic ? ELF::SHT_SYMTAB : ELF::SHT_DYNSYM;
-  SHeader.sh_link = IsStatic ? SN2I.get(".strtab") : SN2I.get(".dynstr");
+
+  // When we describe the .dynsym section in the document explicitly, it is
+  // allowed to omit the "DynamicSymbols" tag. In this case .dynstr is not added
+  // implicitly and we should be able to leave the Link zeroed if .dynstr is not
+  // defined.
+  unsigned Link = 0;
+  if (IsStatic)
+    Link = SN2I.get(".strtab");
+  else
+    SN2I.lookup(".dynstr", Link);
+  SHeader.sh_link = Link;
+
   if (!IsStatic)
     SHeader.sh_flags |= ELF::SHF_ALLOC;