[PATCH] D74479: [llvm-readobj] - Report a warning when an unexpected DT_SYMENT tag value is met.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
grimar added reviewers: jhenderson, MaskRay.
Herald added subscribers: rupprecht, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

There was a short discussion about this:
https://reviews.llvm.org/D73484#inline-676942

To summarize:
It is a bit unclear to me why the `DT_SYMENT` tag exist.
LLD has the code that does:
"addInt(DT_SYMENT, sizeof(Elf_Sym));" and I guess other linkers has the same logic.
It is unclear why it can be possible to have other values rather than values of
a size of platform symbol. Seems it is not possible, and atm for me it looks that
this tag should not be used. This patch starts reporting the warning when the
value it contains differs from a symbol size for a 32/64 bit platform for safety.
It keeps the rest of the logic we have unchanged. Before this patch we did not handle
the tag at all.


https://reviews.llvm.org/D74479

Files:
  llvm/test/tools/llvm-readobj/ELF/dyn-symbols.test
  llvm/tools/llvm-readobj/ELFDumper.cpp


Index: llvm/tools/llvm-readobj/ELFDumper.cpp
===================================================================
--- llvm/tools/llvm-readobj/ELFDumper.cpp
+++ llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -2060,6 +2060,16 @@
       }
       break;
     }
+    case ELF::DT_SYMENT: {
+      uint64_t Val = Dyn.getVal();
+      if (Val != sizeof(Elf_Sym))
+        reportWarning(
+            createError(
+                "DT_SYMENT value contains the unexpected symbol size of 0x" +
+                Twine::utohexstr(Val)),
+            ObjF->getFileName());
+      break;
+    }
     case ELF::DT_RELA:
       DynRelaRegion.Addr = toMappedAddr(Dyn.getTag(), Dyn.getPtr());
       break;
Index: llvm/test/tools/llvm-readobj/ELF/dyn-symbols.test
===================================================================
--- llvm/test/tools/llvm-readobj/ELF/dyn-symbols.test
+++ llvm/test/tools/llvm-readobj/ELF/dyn-symbols.test
@@ -355,6 +355,7 @@
 # RUN: yaml2obj %s --docnum=10 -o %t10
 # RUN: llvm-readobj --dyn-symbols %t10 2>&1 | FileCheck %s -DFILE=%t10 --check-prefix=DYNSYM-SIZE-INVALID1
 # RUN: llvm-readelf --dyn-symbols %t10 2>&1 | FileCheck %s -DFILE=%t10 --check-prefix=DYNSYM-SIZE-INVALID1
+
 ## b) The same, but the DT_SYMTAB tag is present. In this case the dynamic tag has priority over the
 ##    information about a location and an entity size of the dynamic symbol table from the section header.
 ##    The code uses sizeof(Elf_Sym) for an entity size, so it can't be incorrect and
@@ -363,10 +364,21 @@
 # RUN: llvm-readobj --dyn-symbols %t11 2>&1 | FileCheck %s -DFILE=%t11 --check-prefix=DYNSYM-SIZE-INVALID2
 # RUN: llvm-readelf --dyn-symbols %t11 2>&1 | FileCheck %s -DFILE=%t11 --check-prefix=DYNSYM-SIZE-INVALID2
 
+## c) In the case when the DT_SYMENT tag is present, we report when it's value does not match the
+#     value of the symbol size for the platform.
+# RUN: yaml2obj %s -D BITS=32 --docnum=12 -o %t12
+# RUN: llvm-readobj --dyn-symbols %t12 2>&1 | FileCheck %s -DFILE=%t12 --check-prefix=DYNSYM-SIZE-INVALID3
+# RUN: llvm-readelf --dyn-symbols %t12 2>&1 | FileCheck %s -DFILE=%t12 --check-prefix=DYNSYM-SIZE-INVALID3
+# RUN: yaml2obj %s -D BITS=64 --docnum=12 -o %t13
+# RUN: llvm-readobj --dyn-symbols %t13 2>&1 | FileCheck %s -DFILE=%t13 --check-prefix=DYNSYM-SIZE-INVALID3
+# RUN: llvm-readelf --dyn-symbols %t13 2>&1 | FileCheck %s -DFILE=%t13 --check-prefix=DYNSYM-SIZE-INVALID3
+
 # DYNSYM-SIZE-INVALID1: warning: '[[FILE]]': section with index 1 has invalid size (0x1) or entry size (0x10)
 
 # DYNSYM-SIZE-INVALID2: warning: '[[FILE]]': section with index 2 has invalid size (0x1){{$}}
 
+# DYNSYM-SIZE-INVALID3: warning: '[[FILE]]': DT_SYMENT value contains the unexpected symbol size of 0x123{{$}}
+
 --- !ELF
 FileHeader:
   Class:   ELFCLASS32
@@ -401,3 +413,18 @@
     VAddr: 0x100
     Sections:
       - Section: .dynsym
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS[[BITS]]
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name:    .dynamic
+    Type:    SHT_DYNAMIC
+    Entries:
+      - Tag:   DT_SYMENT
+        Value: 0x123
+      - Tag:   DT_NULL
+        Value: 0


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