[PATCH] D56554: [ELF] Add '-z nognustack' opt to suppress emitting PT_GNU_STACK

[Michał Górny via Phabricator via llvm-commits]

mgorny created this revision.
mgorny added reviewers: ruiu, krytarowski.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.

Add a new '-z nognustack' option that suppresses emitting PT_GNU_STACK
segment.  This segment is not supported at all on NetBSD (stack is
always non-executable), and the option is meant to be used to disable
emitting it.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D56554

Files:
  ELF/Config.h
  ELF/Driver.cpp
  ELF/Writer.cpp
  docs/ld.lld.1
  test/ELF/gnustack.s


Index: test/ELF/gnustack.s
===================================================================
--- test/ELF/gnustack.s
+++ test/ELF/gnustack.s
@@ -10,6 +10,9 @@
 # RUN: ld.lld %t1 -o %t -z noexecstack
 # RUN: llvm-readobj --program-headers -s %t | FileCheck --check-prefix=RW %s
 
+# RUN: ld.lld %t1 -o %t -z nognustack
+# RUN: llvm-readobj --program-headers -s %t | FileCheck --check-prefix=NOGNUSTACK %s
+
 # RW:      Type: PT_GNU_STACK
 # RW-NEXT: Offset: 0x0
 # RW-NEXT: VirtualAddress: 0x0
@@ -35,5 +38,7 @@
 # RWX-NEXT: ]
 # RWX-NEXT: Alignment: 0
 
+# NOGNUSTACK-NOT: Type: PT_GNU_STACK
+
 .globl _start
 _start:
Index: docs/ld.lld.1
===================================================================
--- docs/ld.lld.1
+++ docs/ld.lld.1
@@ -509,6 +509,10 @@
 .Dv DF_1_NOOPEN
 flag to indicate that the object may not be opened by
 .Xr dlopen 3 .
+.It Cm nognustack
+Do not emit the
+.Dv PT_GNU_STACK
+segment.
 .It Cm norelro
 Do not indicate that portions of the object shold be mapped read-only
 after initial relocation processing.
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1976,14 +1976,16 @@
   if (OutputSection *Cmd = findSection(".openbsd.randomdata"))
     AddHdr(PT_OPENBSD_RANDOMIZE, Cmd->getPhdrFlags())->add(Cmd);
 
-  // PT_GNU_STACK is a special section to tell the loader to make the
-  // pages for the stack non-executable. If you really want an executable
-  // stack, you can pass -z execstack, but that's not recommended for
-  // security reasons.
-  unsigned Perm = PF_R | PF_W;
-  if (Config->ZExecstack)
-    Perm |= PF_X;
-  AddHdr(PT_GNU_STACK, Perm)->p_memsz = Config->ZStackSize;
+  if (!Config->ZNognustack) {
+    // PT_GNU_STACK is a special section to tell the loader to make the
+    // pages for the stack non-executable. If you really want an executable
+    // stack, you can pass -z execstack, but that's not recommended for
+    // security reasons.
+    unsigned Perm = PF_R | PF_W;
+    if (Config->ZExecstack)
+      Perm |= PF_X;
+    AddHdr(PT_GNU_STACK, Perm)->p_memsz = Config->ZStackSize;
+  }
 
   // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
   // is expected to perform W^X violations, such as calling mprotect(2) or
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -352,6 +352,7 @@
          S == "keep-text-section-prefix" || S == "lazy" || S == "muldefs" ||
          S == "nocombreloc" || S == "nocopyreloc" || S == "nodefaultlib" ||
          S == "nodelete" || S == "nodlopen" || S == "noexecstack" ||
+         S == "nognustack" ||
          S == "nokeep-text-section-prefix" || S == "norelro" || S == "notext" ||
          S == "now" || S == "origin" || S == "relro" || S == "retpolineplt" ||
          S == "rodynamic" || S == "text" || S == "wxneeded" ||
@@ -870,6 +871,7 @@
   Config->ZCopyreloc = getZFlag(Args, "copyreloc", "nocopyreloc", true);
   Config->ZExecstack = getZFlag(Args, "execstack", "noexecstack", false);
   Config->ZGlobal = hasZOption(Args, "global");
+  Config->ZNognustack = hasZOption(Args, "nognustack");
   Config->ZHazardplt = hasZOption(Args, "hazardplt");
   Config->ZInitfirst = hasZOption(Args, "initfirst");
   Config->ZInterpose = hasZOption(Args, "interpose");
Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -193,6 +193,7 @@
   bool ZNodefaultlib;
   bool ZNodelete;
   bool ZNodlopen;
+  bool ZNognustack;
   bool ZNow;
   bool ZOrigin;
   bool ZRelro;


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