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From: Ed Maste <emaste@FreeBSD.org>
Date: Tue, 5 Jan 2016 15:52:17 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r293201 - head/libexec/rtld-elf
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Author: emaste
Date: Tue Jan  5 15:52:16 2016
New Revision: 293201
URL: https://svnweb.freebsd.org/changeset/base/293201

Log:
  rtld: populate DT_DEBUG iff DYNAMIC segment is writable
  
  MIPS has/had a read-only DYNAMIC segment, and uses an extra level of
  indirection (through MIPS_RLD_MAP) to locate the debugger rendezvous
  data.
  
  Some linkers (e.g. LLVM's lld) may produce MIPS binaries with a writable
  DYNAMIC segment, which would allow us to eventually drop a special case.
  
  Therefore, instead of hardcoding knowledge that DYNAMIC is not writable
  on MIPS just check the permissions on the segment.
  
  Reviewed by:	kib
  MFC after:	2 weeks
  Sponsored by:	The FreeBSD Foundation
  Differential Revision:	https://reviews.freebsd.org/D4791

Modified:
  head/libexec/rtld-elf/rtld.c

Modified: head/libexec/rtld-elf/rtld.c
==============================================================================
--- head/libexec/rtld-elf/rtld.c	Tue Jan  5 15:50:50 2016	(r293200)
+++ head/libexec/rtld-elf/rtld.c	Tue Jan  5 15:52:16 2016	(r293201)
@@ -1144,13 +1144,13 @@ digest_dynamic1(Obj_Entry *obj, int earl
 	 * is mapped read-only. DT_MIPS_RLD_MAP is used instead.
 	 */
 
-#ifndef __mips__
 	case DT_DEBUG:
+	    if (!obj->writable_dynamic)
+		break;
 	    if (!early)
 		dbg("Filling in DT_DEBUG entry");
 	    ((Elf_Dyn*)dynp)->d_un.d_ptr = (Elf_Addr) &r_debug;
 	    break;
-#endif
 
 	case DT_FLAGS:
 		if (dynp->d_un.d_val & DF_ORIGIN)
@@ -1331,6 +1331,8 @@ digest_phdr(const Elf_Phdr *phdr, int ph
 	    break;
 
 	case PT_DYNAMIC:
+	    if (ph->p_flags & PROT_WRITE)
+		obj->writable_dynamic = true;
 	    obj->dynamic = (const Elf_Dyn *)(ph->p_vaddr + obj->relocbase);
 	    break;