Fix a serious performance bug for large programs on the Alpha,

discovered by Hidetoshi Shimokawa.  Large programs need multiple
GOTs.  The lazy binding stub in the PLT can be reached from any of
these GOTs, but the dynamic linker only has enough information to
fix up the first GOT entry.  Thus calls through the other GOTs went
through the time-consuming lazy binding process on every call.

This fix rewrites the PLT entries themselves to bypass the lazy
binding.

Tested by Hidetoshi Shimokawa and Steve Price.

Reviewed by:	Doug Rabson <dfr@freebsd.org>

2 files changed, 30 insertions, 26 deletions

diff --git a/libexec/rtld-elf/i386/reloc.c b/libexec/rtld-elf/i386/reloc.c
index 82c0e8e..bdae921 100644
--- a/libexec/rtld-elf/i386/reloc.c
+++ b/libexec/rtld-elf/i386/reloc.c
@@ -1,5 +1,5 @@
 /*-
- * Copyright 1996-1998 John D. Polstra.
+ * Copyright 1996, 1997, 1998, 1999 John D. Polstra.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -22,7 +22,7 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *      $Id: reloc.c,v 1.1 1998/09/04 19:03:57 dfr Exp $
+ *      $Id: reloc.c,v 1.2 1999/04/09 00:28:43 jdp Exp $
  */
 
 /*
@@ -214,33 +214,29 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
 int
 reloc_plt(Obj_Entry *obj, bool bind_now)
 {
-	const Elf_Rel *rellim;
-	const Elf_Rel *rel;
+    const Elf_Rel *rellim;
+    const Elf_Rel *rel;
 
-	/* Process the PLT relocations. */
-	rellim = (const Elf_Rel *) ((caddr_t) obj->pltrel + obj->pltrelsize);
-	if (bind_now) {
-	    /* Fully resolve procedure addresses now */
-	    for (rel = obj->pltrel;  rel < rellim;  rel++) {
-		Elf_Addr *where = (Elf_Addr *)
-		  (obj->relocbase + rel->r_offset);
-		const Elf_Sym *def;
-		const Obj_Entry *defobj;
+    rellim = (const Elf_Rel *)((char *)obj->pltrel + obj->pltrelsize);
+    for (rel = obj->pltrel;  rel < rellim;  rel++) {
+	Elf_Addr *where;
 
-		assert(ELF_R_TYPE(rel->r_info) == R_386_JMP_SLOT);
+	assert(ELF_R_TYPE(rel->r_info) == R_386_JMP_SLOT);
 
-		def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
-		if (def == NULL)
-		    return -1;
+	/* Relocate the GOT slot pointing into the PLT. */
+	where = (Elf_Addr *)(obj->relocbase + rel->r_offset);
+	*where += (Elf_Addr)obj->relocbase;
 
-		*where = (Elf_Addr) (defobj->relocbase + def->st_value);
-	    }
-	} else {	/* Just relocate the GOT slots pointing into the PLT */
-	    for (rel = obj->pltrel;  rel < rellim;  rel++) {
-		Elf_Addr *where = (Elf_Addr *)
-		  (obj->relocbase + rel->r_offset);
-		*where += (Elf_Addr) obj->relocbase;
-	    }
+	if (bind_now) {	/* Fully resolve the procedure address. */
+	    const Elf_Sym *def;
+	    const Obj_Entry *defobj;
+
+	    def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
+	    if (def == NULL)
+		return -1;
+	    reloc_jmpslot(where,
+	      (Elf_Addr)(defobj->relocbase + def->st_value));
 	}
+    }
     return 0;
 }
diff --git a/libexec/rtld-elf/i386/rtld_machdep.h b/libexec/rtld-elf/i386/rtld_machdep.h
index 89a9322..fe39d43 100644
--- a/libexec/rtld-elf/i386/rtld_machdep.h
+++ b/libexec/rtld-elf/i386/rtld_machdep.h
@@ -23,7 +23,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id$
+ *	$Id: rtld_machdep.h,v 1.1 1999/04/09 00:28:43 jdp Exp $
  */
 
 #ifndef RTLD_MACHDEP_H
@@ -33,4 +33,12 @@
 #define rtld_dynamic(obj) \
     ((const Elf_Dyn *)((obj)->relocbase + (Elf_Addr)&_DYNAMIC))
 
+/* Fixup the jump slot at "where" to transfer control to "target". */
+#define reloc_jmpslot(where, target)			\
+    do {						\
+	dbg("reloc_jmpslot: *%p = %p", (void *)(where),	\
+	  (void *)(target));				\
+	(*(Elf_Addr *)(where) = (Elf_Addr)(target));	\
+    } while (0)
+
 #endif