Provide a mechanism for dumping relocation information.

Setting the LD_DUMP_REL_PRE or LD_DUMP_REL_POST environment variables
cause rtld-elf to output a table of all relocations.

This is useful for debugging.

libexec/rtld-elf/debug.c

@@ -33,6 +33,12 @@
 #include <stdio.h>
 
 #include "debug.h"
+#include "rtld.h"
+
+static const char rel_header[] =
+    " symbol name               r_info r_offset st_value st_size    address    value\n"
+    " ------------------------------------------------------------------------------\n";
+static const char rel_format[] =  " %-25s %6x %08x %08x %7d %10p %08x\n";
 
 int debug = 0;
 
@@ -50,3 +56,88 @@ debug_printf(const char *format, ...)
 	va_end(ap);
     }
 }
+
+void
+dump_relocations (Obj_Entry *obj0)
+{
+    Obj_Entry *obj;
+
+    for (obj = obj0; obj != NULL; obj = obj->next) {
+        dump_obj_relocations(obj);
+    }
+}
+
+void
+dump_obj_relocations (Obj_Entry *obj)
+{
+
+    printf("Object \"%s\", relocbase %p\n", obj->path, obj->relocbase);
+
+    if (obj->relsize) {
+        printf("Non-PLT Relocations: %ld\n",
+            (obj->relsize / sizeof(Elf_Rel)));
+        dump_Elf_Rel(obj, obj->rel, obj->relsize);
+    }
+
+    if (obj->relasize) {
+        printf("Non-PLT Relocations with Addend: %ld\n",
+            (obj->relasize / sizeof(Elf_Rela)));
+        dump_Elf_Rela(obj, obj->rela, obj->relasize);
+    }
+
+    if (obj->pltrelsize) {
+        printf("PLT Relocations: %ld\n",
+            (obj->pltrelsize / sizeof(Elf_Rel)));
+        dump_Elf_Rel(obj, obj->pltrel, obj->pltrelsize);
+    }
+
+    if (obj->pltrelasize) {
+        printf("PLT Relocations with Addend: %ld\n",
+            (obj->pltrelasize / sizeof(Elf_Rela)));
+        dump_Elf_Rela(obj, obj->pltrela, obj->pltrelasize);
+    }
+}
+
+void
+dump_Elf_Rel (Obj_Entry *obj, const Elf_Rel *rel0, u_long relsize)
+{
+    const Elf_Rel *rel;
+    const Elf_Rel *rellim;
+    const Elf_Sym *sym;
+    Elf_Addr *dstaddr;
+
+    printf("%s", rel_header);
+    rellim = (const Elf_Rel *)((char *)rel0 + relsize);
+    for (rel = rel0; rel < rellim; rel++) {
+	dstaddr = (Elf_Addr *)(obj->relocbase + rel->r_offset);
+        sym = obj->symtab + ELF_R_SYM(rel->r_info);
+        printf(rel_format,
+		obj->strtab + sym->st_name,
+		rel->r_info, rel->r_offset,
+		sym->st_value, sym->st_size,
+		dstaddr, *dstaddr);
+    }
+    return;
+}
+
+void
+dump_Elf_Rela (Obj_Entry *obj, const Elf_Rela *rela0, u_long relasize)
+{
+    const Elf_Rela *rela;
+    const Elf_Rela *relalim;
+    const Elf_Sym *sym;
+    Elf_Addr *dstaddr;
+
+    printf("%s", rel_header);
+    relalim = (const Elf_Rela *)((char *)rela0 + relasize);
+    for (rela = rela0; rela < relalim; rela++) {
+	dstaddr = (Elf_Addr *)(obj->relocbase + rela->r_offset);
+        sym = obj->symtab + ELF_R_SYM(rela->r_info);
+        printf(rel_format,
+		obj->strtab + sym->st_name,
+		rela->r_info, rela->r_offset,
+		sym->st_value, sym->st_size,
+		dstaddr, *dstaddr);
+    }
+    return;
+}

libexec/rtld-elf/rtld.1

@@ -83,6 +83,16 @@ recognizes a number of environment variables that can be used to modify
 its behaviour as follows:
 .Pp
 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
+.It Ev LD_DUMP_REL_POST
+If set
+.Nm
+will print (to stderr) a table containing all relocations after symbol
+binding and relocation.
+.It Ev LD_DUMP_REL_PRE
+If set
+.Nm
+will print (to stderr) a table containing all relocations before symbol
+binding and relocation.
 .It Ev LD_LIBMAP_DISABLE
 If set, disables the use of
 .Xr libmap.conf 5 .

libexec/rtld-elf/rtld.c

@@ -365,6 +365,11 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
 	exit(0);
     }
 
+    if (getenv("LD_DUMP_REL_PRE") != NULL) {
+       dump_relocations(obj_main);
+       exit (0);
+    }
+
     if (relocate_objects(obj_main,
 	ld_bind_now != NULL && *ld_bind_now != '\0', &obj_rtld) == -1)
 	die();
@@ -373,6 +378,11 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
     if (do_copy_relocations(obj_main) == -1)
 	die();
 
+    if (getenv("LD_DUMP_REL_POST") != NULL) {
+       dump_relocations(obj_main);
+       exit (0);
+    }
+
     dbg("initializing key program variables");
     set_program_var("__progname", argv[0] != NULL ? basename(argv[0]) : "");
     set_program_var("environ", env);

libexec/rtld-elf/rtld.h

@@ -186,6 +186,11 @@ extern void *xmalloc(size_t);
 extern char *xstrdup(const char *);
 extern Elf_Addr _GLOBAL_OFFSET_TABLE_[];
 
+extern void dump_relocations (Obj_Entry *);
+extern void dump_obj_relocations (Obj_Entry *);
+extern void dump_Elf_Rel (Obj_Entry *, const Elf_Rel *, u_long);
+extern void dump_Elf_Rela (Obj_Entry *, const Elf_Rela *, u_long);
+
 /*
  * Function declarations.
  */