[PATCH] D33251: [lld][ELF]Add option to make .dynamic read only

[Jake Ehrlich via Phabricator via llvm-commits]

jakehehrlich updated this revision to Diff 100329.
jakehehrlich added a comment.

I made the changes Rui recommended.


Repository:
  rL LLVM

https://reviews.llvm.org/D33251

Files:
  ELF/Config.h
  ELF/Driver.cpp
  ELF/SyntheticSections.cpp
  test/ELF/rodynamic.s


Index: test/ELF/rodynamic.s
===================================================================
--- /dev/null
+++ test/ELF/rodynamic.s
@@ -0,0 +1,13 @@
+# RUN: llvm-mc %s -o %t.o -filetype=obj -triple=x86_64-pc-linux
+# RUN: ld.lld -shared -z rodynamic %t.o -o %t.so
+# RUN: llvm-readobj -sections %t.so | FileCheck %s
+
+.globl _start
+_start:
+
+# CHECK:      Section {
+# CHECK:        Name: .dynamic
+# CHECK-NEXT:   Type: SHT_DYNAMIC
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_ALLOC
+# CHECK-NEXT:   ]
Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -1005,10 +1005,11 @@
                        ".dynamic") {
   this->Entsize = ELFT::Is64Bits ? 16 : 8;
 
-  // .dynamic section is not writable on MIPS.
+  // .dynamic section is not writable on MIPS and on Fuchsia OS
+  // which passes -z rodynamic.
   // See "Special Section" in Chapter 4 in the following document:
   // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
-  if (Config->EMachine == EM_MIPS)
+  if (Config->EMachine == EM_MIPS || Config->ZReadOnlyDynamic)
     this->Flags = SHF_ALLOC;
 
   addEntries();
@@ -1053,7 +1054,14 @@
   if (DtFlags1)
     add({DT_FLAGS_1, DtFlags1});
 
-  if (!Config->Shared && !Config->Relocatable)
+  // DT_DEBUG is a pointer to debug informaion used by debuggers at runtime.
+  // We need it for each process, so we don't write it for DSOs.
+  // The loader writes the pointer into this entry.
+  // DT_DEBUG is the only .dynamic entry that needs to be written to.
+  // Some systems (like Fuchsia OS) provide other means to give the debugger
+  // this information. Such systems may choose make .dynamic read-only.
+  // If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
+  if (!Config->Shared && !Config->Relocatable && !Config->ZReadOnlyDynamic)
     add({DT_DEBUG, (uint64_t)0});
 }
 
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -687,6 +687,7 @@
   Config->ZNodlopen = hasZOption(Args, "nodlopen");
   Config->ZNow = hasZOption(Args, "now");
   Config->ZOrigin = hasZOption(Args, "origin");
+  Config->ZReadOnlyDynamic = hasZOption(Args, "rodynamic");
   Config->ZRelro = !hasZOption(Args, "norelro");
   Config->ZStackSize = getZOptionValue(Args, "stack-size", 0);
   Config->ZText = !hasZOption(Args, "notext");
Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -144,6 +144,7 @@
   bool ZNodlopen;
   bool ZNow;
   bool ZOrigin;
+  bool ZReadOnlyDynamic;
   bool ZRelro;
   bool ZText;
   bool ExitEarly;


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