svn commit: r314115 - head/libexec/rtld-elf/mips

[John Baldwin]

Author: jhb
Date: Thu Feb 23 00:02:49 2017
New Revision: 314115
URL: https://svnweb.freebsd.org/changeset/base/314115

Log:
  Fully handle the special encoding of GOT[1] on mips64.
  
  The MIPS ABI does not require the second GOT entry to be reserved for use
  by the runtime linker as on other architectures.  Instead, static linkers
  use a special value in the second GOT entry to indicate if the entry is
  reserved.  This value is supposed to consist of an address with the MSB
  set and the rest of the bits all zero which is an invalid user address.
  
  However, the old binutils currently in the tree uses the 32-bit mask value
  (2^31) on 64-bit MIPS instead of 2^63.  This was fixed in upstream
  binutils in 2008 to use 2^63 on 64-bit MIPS.
  
  The first part of this change changes the runtime check in init_pltgot()
  to check for both values (2^31 and 2^63) when deciding whether to store
  the current object pointer in GOT[1] which fixes dynamic N64 binaries
  compiled with modern binutils.
  
  However, the initial version of this fix exposed another related bug in
  that _rtld_relocate_nonplt_self() was only checking for the new value
  (2^63) in GOT[1] and incorrectly treated GOT[1] as a local GOT entry
  (and did not relocate the final local GOT entry).  To handle this, fix
  all of the places that check for GOT[1]'s status to use the same macro
  that checks for both values on N64.
  
  Reviewed by:	kan, imp
  Sponsored by:	DARPA / AFRL
  Differential Revision:	https://reviews.freebsd.org/D9708

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

Modified: head/libexec/rtld-elf/mips/reloc.c
==============================================================================
--- head/libexec/rtld-elf/mips/reloc.c	Wed Feb 22 23:58:54 2017	(r314114)
+++ head/libexec/rtld-elf/mips/reloc.c	Thu Feb 23 00:02:49 2017	(r314115)
@@ -51,12 +51,28 @@ __FBSDID("$FreeBSD$");
 #define	GOT1_MASK	0x80000000UL
 #endif
 
+/*
+ * Determine if the second GOT entry is reserved for rtld or if it is
+ * the first "real" GOT entry.
+ *
+ * This must be a macro rather than a function so that
+ * _rtld_relocate_nonplt_self doesn't trigger a GOT invocation trying
+ * to use it before the local GOT entries in rtld are adjusted.
+ */
+#ifdef __mips_n64
+/* Old binutils uses the 32-bit GOT1 mask value for N64. */
+#define GOT1_RESERVED_FOR_RTLD(got)					\
+	(((got)[1] == 0x80000000) || (got)[1] & GOT1_MASK)
+#else
+#define GOT1_RESERVED_FOR_RTLD(got)	((got)[1] & GOT1_MASK)
+#endif
+
 void
 init_pltgot(Obj_Entry *obj)
 {
 	if (obj->pltgot != NULL) {
 		obj->pltgot[0] = (Elf_Addr) &_rtld_bind_start;
-		if (obj->pltgot[1] & 0x80000000)
+		if (GOT1_RESERVED_FOR_RTLD(obj->pltgot))
 			obj->pltgot[1] = (Elf_Addr) obj | GOT1_MASK;
 	}
 }
@@ -175,7 +191,7 @@ _rtld_relocate_nonplt_self(Elf_Dyn *dynp
 		}
 	}
 
-	i = (got[1] & GOT1_MASK) ? 2 : 1;
+	i = GOT1_RESERVED_FOR_RTLD(got) ? 2 : 1;
 	/* Relocate the local GOT entries */
 	got += i;
 	for (; i < local_gotno; i++) {
@@ -294,7 +310,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry 
 	dbg("%s: broken=%d", obj->path, broken);
 #endif
 
-	i = (got[1] & GOT1_MASK) ? 2 : 1;
+	i = GOT1_RESERVED_FOR_RTLD(got) ? 2 : 1;
 
 	/* Relocate the local GOT entries */
 	got += i;