[PATCH] D49456: [AArch64] Support execute-only LOAD segments.

[Ivan Lozano via Phabricator via llvm-commits]

ivanlozano created this revision.
ivanlozano added reviewers: srhines, echristo, peter.smith, eugenis.
Herald added subscribers: llvm-commits, kristof.beyls, arichardson, emaste.
Herald added a reviewer: javed.absar.
Herald added a reviewer: espindola.

This adds an LLD flag to mark executable LOAD segments execute-only for AArch64 targets.

In AArch64 the expectation is that code is execute-only compatible, so this just adds a linker option to enforce this.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D49456

Files:
  ELF/Config.h
  ELF/Driver.cpp
  ELF/Options.td
  ELF/Writer.cpp
  test/ELF/aarch64_execute_only.s


Index: test/ELF/aarch64_execute_only.s
===================================================================
--- /dev/null
+++ test/ELF/aarch64_execute_only.s
@@ -0,0 +1,12 @@
+// REQUIRES: aarch64
+
+// RUN: llvm-mc -filetype=obj -triple=aarch64-linux-none %s -o %t.o
+// RUN: ld.lld %t.o -o %t.so -shared -aarch64-execute-only
+// RUN: llvm-readelf -l %t.so | FileCheck %s
+
+// CHECK:      LOAD           0x{{.*}} 0x{{.*}} 0x{{.*}} 0x{{.*}} 0x{{.*}}   E 0x{{.*}}
+// CHECK-NOT:  LOAD           0x{{.*}} 0x{{.*}} 0x{{.*}} 0x{{.*}} 0x{{.*}} R E 0x{{.*}}
+
+        br lr
+        .section .foo,"ax"
+        br lr
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1768,6 +1768,9 @@
     return PF_R | PF_W | PF_X;
   if (Config->SingleRoRx && !(Flags & PF_W))
     return Flags | PF_X;
+  if (Config->EMachine == EM_AARCH64 && Config->AArch64ExecuteOnly &&
+      (Flags & PF_X))
+    return Flags & ~PF_R;
   return Flags;
 }
 
Index: ELF/Options.td
===================================================================
--- ELF/Options.td
+++ ELF/Options.td
@@ -243,6 +243,10 @@
     "Create a position independent executable",
     "Do not create a position independent executable (default)">;
 
+defm aarch64_execute_only: B<"aarch64-execute-only",
+    "Do not mark executable sections readable.",
+    "Mark executable sections readable.">;
+
 defm print_gc_sections: B<"print-gc-sections",
     "List removed unused sections",
     "Do not list removed unused sections (default)">;
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -299,6 +299,14 @@
     if (Config->Pie)
       error("-r and -pie may not be used together");
   }
+
+  if (Config->AArch64ExecuteOnly) {
+    if (Config->EMachine != EM_AARCH64)
+      error("-aarch64-execute-only is only supported on AArch64 targets.");
+
+    if (Config->SingleRoRx)
+      error("-aarch64-execute-only and -no-rosegment cannot be used together.");
+  }
 }
 
 static const char *getReproduceOption(opt::InputArgList &Args) {
@@ -735,6 +743,8 @@
   Config->EnableNewDtags =
       Args.hasFlag(OPT_enable_new_dtags, OPT_disable_new_dtags, true);
   Config->Entry = Args.getLastArgValue(OPT_entry);
+  Config->AArch64ExecuteOnly = Args.hasFlag(OPT_aarch64_execute_only,
+                                            OPT_no_aarch64_execute_only, false);
   Config->ExportDynamic =
       Args.hasFlag(OPT_export_dynamic, OPT_no_export_dynamic, false);
   Config->FilterList = args::getStrings(Args, OPT_filter);
Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -113,6 +113,7 @@
   llvm::MapVector<std::pair<const InputSectionBase *, const InputSectionBase *>,
                   uint64_t>
       CallGraphProfile;
+  bool AArch64ExecuteOnly;
   bool AllowMultipleDefinition;
   bool AndroidPackDynRelocs;
   bool ARMHasBlx = false;


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