From e278d94bcaa58236dbb6f1849ed7c046ef740193 Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Thu, 23 Feb 2017 00:02:49 +0000
Subject: [PATCH] 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
---
 libexec/rtld-elf/mips/reloc.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/libexec/rtld-elf/mips/reloc.c b/libexec/rtld-elf/mips/reloc.c
index 1d1e1a174a6a..59dc18800e4c 100644
--- a/libexec/rtld-elf/mips/reloc.c
+++ b/libexec/rtld-elf/mips/reloc.c
@@ -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, Elf_Addr relocbase)
 		}
 	}
 
-	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 *obj_rtld, int flags,
 	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;