[llvm-readelf] - Allow dumping of the .dynamic section even if there is no PT_DYNAMIC header.

George Rimar · George Rimar · commit f835fcf412c9 · 2019-05-24T11:12:50.000Z
It is now possible after D61937 was landed and was discussed in it's review comments. It is not consistent with GNU, which does not output .dynamic section content in this case for no visible reason. Differential revision: https://reviews.llvm.org/D62179 llvm-svn: 361630
diff --git a/llvm/test/tools/llvm-readobj/elf-dynamic-no-pt-dynamic.test b/llvm/test/tools/llvm-readobj/elf-dynamic-no-pt-dynamic.test
@@ -1,16 +1,23 @@
-# Show that no dumping occurs if there is no PT_DYNAMIC header.
+## Show that dumping occurs even if there is no PT_DYNAMIC header.
+## This is inconsistent with the GNU behavior, but seems to be more reasonable.
 # RUN: yaml2obj %s -o %t.no-phdr
 # RUN: llvm-readobj --dynamic-table %t.no-phdr | FileCheck %s --check-prefix=LLVM
-# RUN: llvm-readelf --dynamic-table %t.no-phdr | FileCheck %s --check-prefix=GNU --allow-empty
+# RUN: llvm-readelf --dynamic-table %t.no-phdr | FileCheck %s --check-prefix=GNU
 
 # LLVM:      File: {{.*}}.no-phdr
 # LLVM-NEXT: Format: ELF64-x86-64
 # LLVM-NEXT: Arch: x86_64
 # LLVM-NEXT: AddressSize: 64bit
 # LLVM-NEXT: LoadName:{{ *}}
-# LLVM-NOT:  {{.}}
+# LLVM-NEXT: DynamicSection [ (1 entries)
+# LLVM-NEXT:   Tag                Type Name/Value
+# LLVM-NEXT:   0x0000000000000000 NULL 0x0
+# LLVM-NEXT: ]
 
-# GNU-NOT: {{.}}
+# GNU:      DynamicSection [ (1 entries)
+# GNU-NEXT:   Tag                Type Name/Value
+# GNU-NEXT:   0x0000000000000000 NULL 0x0
+# GNU-NEXT: ]
 
 --- !ELF
 FileHeader:
diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -1331,6 +1331,7 @@ static const char *getElfMipsOptionsOdkType(unsigned Odk) {
 
 template <typename ELFT>
 void ELFDumper<ELFT>::loadDynamicTable(const ELFFile<ELFT> *Obj) {
+  // Try to locate the PT_DYNAMIC header.
   const Elf_Phdr *DynamicPhdr = nullptr;
   for (const Elf_Phdr &Phdr : unwrapOrError(Obj->program_headers())) {
     if (Phdr.p_type != ELF::PT_DYNAMIC)
@@ -1339,11 +1340,6 @@ void ELFDumper<ELFT>::loadDynamicTable(const ELFFile<ELFT> *Obj) {
     break;
   }
 
-  // We do not want to dump dynamic section if we have no PT_DYNAMIC header.
-  // This matches GNU's behavior.
-  if (!DynamicPhdr)
-    return;
-
   // Try to locate the .dynamic section in the sections header table.
   const Elf_Shdr *DynamicSec = nullptr;
   for (const Elf_Shdr &Sec : unwrapOrError(Obj->sections())) {
@@ -1358,9 +1354,16 @@ void ELFDumper<ELFT>::loadDynamicTable(const ELFFile<ELFT> *Obj) {
   // Ignore sh_entsize and use the expected value for entry size explicitly.
   // This allows us to dump the dynamic sections with a broken sh_entsize
   // field.
-  if (DynamicSec)
+  if (DynamicSec) {
     DynamicTable = checkDRI({ObjF->getELFFile()->base() + DynamicSec->sh_offset,
                              DynamicSec->sh_size, sizeof(Elf_Dyn)});
+    parseDynamicTable();
+  }
+
+  // If we have a PT_DYNAMIC header, we will either check the found dynamic
+  // section or take the dynamic table data directly from the header.
+  if (!DynamicPhdr)
+    return;
 
   if (DynamicPhdr->p_offset + DynamicPhdr->p_filesz >
       ObjF->getMemoryBufferRef().getBufferSize())
@@ -1374,7 +1377,6 @@ void ELFDumper<ELFT>::loadDynamicTable(const ELFFile<ELFT> *Obj) {
   }
 
   StringRef Name = unwrapOrError(Obj->getSectionName(DynamicSec));
-
   if (DynamicSec->sh_addr + DynamicSec->sh_size >
           DynamicPhdr->p_vaddr + DynamicPhdr->p_memsz ||
       DynamicSec->sh_addr < DynamicPhdr->p_vaddr)
@@ -1386,8 +1388,6 @@ void ELFDumper<ELFT>::loadDynamicTable(const ELFFile<ELFT> *Obj) {
     reportWarning("The SHT_DYNAMIC section '" + Name +
                   "' is not at the start of "
                   "PT_DYNAMIC segment");
-
-  parseDynamicTable();
 }
 
 template <typename ELFT>
