[llvm-readelf] - Allow dumping dynamic symbols when there is no program headers.

D62179 introduced a regression. llvm-readelf lose the ability to dump the dynamic symbols
when there is .dynamic section with a DT_SYMTAB, but there are no program headers:
https://reviews.llvm.org/D62179#1652778

Below is a program flow before the D62179 change:

1) Find SHT_DYNSYM.
2) Find there is no PT_DYNAMIC => don't try to parse it.
3) Print dynamic symbols using information about them found on step (1).

And after the change it became:

1) Find SHT_DYNSYM.
2) Find there is no PT_DYNAMIC => find SHT_DYNAMIC.
3) Parse dynamic table, but fail to handle the DT_SYMTAB because of the absence of the PT_LOAD. Report the "Virtual address is not in any segment" error.

This patch fixes the issue. For doing this it checks that the value of DT_SYMTAB was
mapped to a segment. If not - it ignores it.

Differential revision: https://reviews.llvm.org/D67078

llvm-svn: 371071

1 files changed, 22 insertions, 3 deletions

diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index b019ed81329..bc173607e7b 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -1643,10 +1643,29 @@ template <typename ELFT> void ELFDumper<ELFT>::parseDynamicTable() {
     case ELF::DT_STRSZ:
       StringTableSize = Dyn.getVal();
       break;
-    case ELF::DT_SYMTAB:
-      DynSymRegion.Addr = toMappedAddr(Dyn.getTag(), Dyn.getPtr());
-      DynSymRegion.EntSize = sizeof(Elf_Sym);
+    case ELF::DT_SYMTAB: {
+      // Often we find the information about the dynamic symbol table
+      // location in the SHT_DYNSYM section header. However, the value in
+      // DT_SYMTAB has priority, because it is used by dynamic loaders to
+      // locate .dynsym at runtime. The location we find in the section header
+      // and the location we find here should match. If we can't map the
+      // DT_SYMTAB value to an address (e.g. when there are no program headers), we
+      // ignore its value.
+      if (const uint8_t *VA = toMappedAddr(Dyn.getTag(), Dyn.getPtr())) {
+        // EntSize is non-zero if the dynamic symbol table has been found via a
+        // section header.
+        if (DynSymRegion.EntSize && VA != DynSymRegion.Addr)
+          reportWarning(
+              createError(
+                  "SHT_DYNSYM section header and DT_SYMTAB disagree about "
+                  "the location of the dynamic symbol table"),
+              ObjF->getFileName());
+
+        DynSymRegion.Addr = VA;
+        DynSymRegion.EntSize = sizeof(Elf_Sym);
+      }
       break;
+    }
     case ELF::DT_RELA:
       DynRelaRegion.Addr = toMappedAddr(Dyn.getTag(), Dyn.getPtr());
       break;