Get the actual pathname of the dynamic linker from the executable's

PT_INTERP program header entry, to ensure that gdb always finds
the right dynamic linker.

Use obj->relocbase to simplify a few calculations where appropriate.

3 files changed, 31 insertions, 12 deletions

diff --git a/libexec/rtld-elf/map_object.c b/libexec/rtld-elf/map_object.c
index ca353c7..d7b6978 100644
--- a/libexec/rtld-elf/map_object.c
+++ b/libexec/rtld-elf/map_object.c
@@ -62,6 +62,7 @@ map_object(int fd, const char *path, const struct stat *sb)
     int nsegs;
     Elf_Phdr *phdyn;
     Elf_Phdr *phphdr;
+    Elf_Phdr *phinterp;
     caddr_t mapbase;
     size_t mapsize;
     Elf_Off base_offset;
@@ -136,11 +137,14 @@ map_object(int fd, const char *path, const struct stat *sb)
     phdr = (Elf_Phdr *) (u.buf + u.hdr.e_phoff);
     phlimit = phdr + u.hdr.e_phnum;
     nsegs = 0;
-    phdyn = NULL;
-    phphdr = NULL;
+    phdyn = phphdr = phinterp = NULL;
     while (phdr < phlimit) {
 	switch (phdr->p_type) {
 
+	case PT_INTERP:
+	    phinterp = phdr;
+	    break;
+
 	case PT_LOAD:
 	    if (nsegs >= 2) {
 		_rtld_error("%s: too many PT_LOAD segments", path);
@@ -239,15 +243,15 @@ map_object(int fd, const char *path, const struct stat *sb)
       base_vaddr;
     obj->vaddrbase = base_vaddr;
     obj->relocbase = mapbase - base_vaddr;
-    obj->dynamic = (const Elf_Dyn *)
-      (mapbase + (phdyn->p_vaddr - base_vaddr));
+    obj->dynamic = (const Elf_Dyn *) (obj->relocbase + phdyn->p_vaddr);
     if (u.hdr.e_entry != 0)
-	obj->entry = (caddr_t) (mapbase + (u.hdr.e_entry - base_vaddr));
+	obj->entry = (caddr_t) (obj->relocbase + u.hdr.e_entry);
     if (phphdr != NULL) {
-	obj->phdr = (const Elf_Phdr *)
-	  (mapbase + (phphdr->p_vaddr - base_vaddr));
+	obj->phdr = (const Elf_Phdr *) (obj->relocbase + phphdr->p_vaddr);
 	obj->phsize = phphdr->p_memsz;
     }
+    if (phinterp != NULL)
+	obj->interp = (const char *) (obj->relocbase + phinterp->p_vaddr);
 
     return obj;
 }
diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
index ef5f917..1885383 100644
--- a/libexec/rtld-elf/rtld.c
+++ b/libexec/rtld-elf/rtld.c
@@ -61,11 +61,8 @@
 #define msg(s)		(write(1, s, strlen(s)))
 #define trace()		msg("trace: " __XSTRING(__LINE__) "\n");
 
-#ifndef _PATH_RTLD
-#define _PATH_RTLD	"/usr/libexec/ld-elf.so.1"
-#endif
-
 #define END_SYM		"_end"
+#define PATH_RTLD	"/usr/libexec/ld-elf.so.1"
 
 /* Types. */
 typedef void (*func_ptr_type)();
@@ -269,6 +266,19 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
 
     obj_main->path = xstrdup(argv0);
     obj_main->mainprog = true;
+
+    /*
+     * Get the actual dynamic linker pathname from the executable if
+     * possible.  (It should always be possible.)  That ensures that
+     * gdb will find the right dynamic linker even if a non-standard
+     * one is being used.
+     */
+    if (obj_main->interp != NULL &&
+      strcmp(obj_main->interp, obj_rtld.path) != 0) {
+	free(obj_rtld.path);
+	obj_rtld.path = xstrdup(obj_main->interp);
+    }
+
     digest_dynamic(obj_main);
 
     linkmap_add(obj_main);
@@ -585,6 +595,10 @@ digest_phdr(const Elf_Phdr *phdr, int phnum, caddr_t entry, const char *path)
 	    obj->phsize = ph->p_memsz;
 	    break;
 
+	case PT_INTERP:
+	    obj->interp = (const char *) ph->p_vaddr;
+	    break;
+
 	case PT_LOAD:
 	    if (nsegs >= 2) {
 		_rtld_error("%s: too many PT_LOAD segments", path);
@@ -867,7 +881,7 @@ init_rtld(caddr_t mapbase)
      * aren't yet initialized sufficiently to do that.  Below we will
      * replace the static version with a dynamically-allocated copy.
      */
-    obj_rtld.path = _PATH_RTLD;
+    obj_rtld.path = PATH_RTLD;
     obj_rtld.rtld = true;
     obj_rtld.mapbase = mapbase;
 #ifdef PIC
diff --git a/libexec/rtld-elf/rtld.h b/libexec/rtld-elf/rtld.h
index ab26d01..0cdbe4c 100644
--- a/libexec/rtld-elf/rtld.h
+++ b/libexec/rtld-elf/rtld.h
@@ -99,6 +99,7 @@ typedef struct Struct_Obj_Entry {
     caddr_t entry;		/* Entry point */
     const Elf_Phdr *phdr;	/* Program header if it is mapped, else NULL */
     size_t phsize;		/* Size of program header in bytes */
+    const char *interp;		/* Pathname of the interpreter, if any */
 
     /* Items from the dynamic section. */
     Elf_Addr *pltgot;		/* PLT or GOT, depending on architecture */