Eliminate unaligned accesses that occurred when relocating the

DWARF2 exception tables emitted by the compiler for C++ sources.
These tables are tightly packed, and they contain some relocated
addresses which are not well-aligned.

1 files changed, 27 insertions, 12 deletions

diff --git a/libexec/rtld-elf/alpha/reloc.c b/libexec/rtld-elf/alpha/reloc.c
index 8763be4..e27f922 100644
--- a/libexec/rtld-elf/alpha/reloc.c
+++ b/libexec/rtld-elf/alpha/reloc.c
@@ -49,6 +49,23 @@
 
 extern Elf_Dyn _DYNAMIC;
 
+/*
+ * Macros for loading/storing unaligned 64-bit values.  These are
+ * needed because relocations can point to unaligned data.  This
+ * occurs in the DWARF2 exception frame tables generated by the
+ * compiler, for instance.
+ *
+ * We don't use these when relocating jump slots and GOT entries,
+ * since they are guaranteed to be aligned.
+ */
+#define load64(p) ({						\
+	Elf_Addr __res;						\
+	__asm__("ldq_u %0,%1" : "=r"(__res) : "m"(*(p)));	\
+	__res; })
+
+#define store64(p, v)						\
+	__asm__("stq_u %1,%0" : "=m"(*(p)) : "r"(v))
+
 /* Relocate a non-PLT object with addend. */
 static int
 reloc_non_plt_obj(Obj_Entry *obj_rtld, Obj_Entry *obj, const Elf_Rela *rela)
@@ -63,33 +80,30 @@ reloc_non_plt_obj(Obj_Entry *obj_rtld, Obj_Entry *obj, const Elf_Rela *rela)
 		case R_ALPHA_REFQUAD: {
 			const Elf_Sym *def;
 			const Obj_Entry *defobj;
-			Elf_Addr tmp_value;
 
 			def = find_symdef(ELF_R_SYM(rela->r_info), obj,
 			    &defobj, false);
 			if (def == NULL)
 				return -1;
-
-			tmp_value = (Elf_Addr) (defobj->relocbase +
-			    def->st_value) + *where + rela->r_addend;
-			if (*where != tmp_value)
-				*where = tmp_value;
+			store64(where,
+			    (Elf_Addr) (defobj->relocbase + def->st_value) +
+			    load64(where) + rela->r_addend);
 		}
 		break;
 
 		case R_ALPHA_GLOB_DAT: {
 			const Elf_Sym *def;
 			const Obj_Entry *defobj;
+			Elf_Addr val;
 
 			def = find_symdef(ELF_R_SYM(rela->r_info), obj,
 			    &defobj, false);
 			if (def == NULL)
 				return -1;
-
-			if (*where != (Elf_Addr) (defobj->relocbase +
-			    def->st_value + rela->r_addend))
-				*where = (Elf_Addr) (defobj->relocbase +
-				    def->st_value + rela->r_addend);
+			val = (Elf_Addr) (defobj->relocbase + def->st_value +
+			    rela->r_addend);
+			if (load64(where) != val)
+				store64(where, val);
 		}
 		break;
 
@@ -97,7 +111,8 @@ reloc_non_plt_obj(Obj_Entry *obj_rtld, Obj_Entry *obj, const Elf_Rela *rela)
 			if (obj != obj_rtld ||
 			    (caddr_t)where < (caddr_t)_GLOBAL_OFFSET_TABLE_ ||
 			    (caddr_t)where >= (caddr_t)&_DYNAMIC)
-				*where += (Elf_Addr) obj->relocbase;
+				store64(where,
+				    load64(where) + (Elf_Addr) obj->relocbase);
 		}
 		break;