Revert "Fix unwinding of pre-linked libraries"

This reverts commit a4014f3377. The
implementation of the pre-linking support is wrong. It assumes that only
pre-linked libraries will have the virtual address of the LOAD ELF section set
to non-zero.

On arm-linux-gnueabi, without pre-linking, we have:

  LOAD           0x000000 0x00010000 0x00010000 0x267fc 0x267fc R E 0x10000

Which means that load_offset is set to 0x10000 and incorrectly substracted
from ip - ip_base. It also seems that pre-linking support is vastly
deprecated.

Reverting that one fixes .debug_frame based unwinding of arm-linux-gnueabi.

include/dwarf.h

@@ -371,8 +371,6 @@ struct unw_debug_frame_list
     /* The start (inclusive) and end (exclusive) of the described region.  */
     unw_word_t start;
     unw_word_t end;
-    /* ELF load offset */
-    unw_word_t load_offset;
     /* The debug frame itself.  */
     char *debug_frame;
     size_t debug_frame_size;

include/libunwind-dynamic.h

@@ -141,7 +141,6 @@ typedef struct unw_dyn_info
     unw_word_t gp;              /* global-pointer in effect for this entry */
     int32_t format;             /* real type: unw_dyn_info_format_t */
     int32_t pad;
-    unw_word_t load_offset;     /* ELF load offset */
     union
       {
         unw_dyn_proc_info_t pi;

src/dwarf/Gfind_proc_info-lsb.c

@@ -107,17 +107,13 @@ linear_search (unw_addr_space_t as, unw_word_t ip,
 /* XXX: Could use mmap; but elf_map_image keeps tons mapped in.  */
 
 static int
-load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local, unw_word_t *load_offset)
+load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local)
 {
   struct elf_image ei;
-  Elf_W (Ehdr) *ehdr;
-  Elf_W (Phdr) *phdr;
   Elf_W (Shdr) *shdr;
-  int i;
   int ret;
 
   ei.image = NULL;
-  *load_offset = 0;
 
   ret = elf_w (load_debuginfo) (file, &ei, is_local);
   if (ret != 0)
@@ -192,20 +188,6 @@ load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local, u
 #if defined(SHF_COMPRESSED)
     }
 #endif
-
-  ehdr = ei.image;
-  phdr = (Elf_W (Phdr) *) ((char *) ei.image + ehdr->e_phoff);
-
-  for (i = 0; i < ehdr->e_phnum; ++i)
-    if (phdr[i].p_type == PT_LOAD)
-      {
-        *load_offset = phdr[i].p_vaddr;
-
-        Debug (4, "%s load offset is 0x%zx\n", file, *load_offset);
-
-        break;
-      }
-
   mi_munmap(ei.image, ei.size);
   return 0;
 }
@@ -258,7 +240,6 @@ locate_debug_info (unw_addr_space_t as, unw_word_t addr, const char *dlname,
   int err;
   char *buf;
   size_t bufsize;
-  unw_word_t load_offset;
 
   /* First, see if we loaded this frame already.  */
 
@@ -285,7 +266,7 @@ locate_debug_info (unw_addr_space_t as, unw_word_t addr, const char *dlname,
   else
     name = (char*) dlname;
 
-  err = load_debug_frame (name, &buf, &bufsize, as == unw_local_addr_space, &load_offset);
+  err = load_debug_frame (name, &buf, &bufsize, as == unw_local_addr_space);
 
   if (!err)
     {
@@ -298,7 +279,6 @@ locate_debug_info (unw_addr_space_t as, unw_word_t addr, const char *dlname,
 
       fdesc->start = start;
       fdesc->end = end;
-      fdesc->load_offset = load_offset;
       fdesc->debug_frame = buf;
       fdesc->debug_frame_size = bufsize;
       fdesc->index = NULL;
@@ -494,7 +474,6 @@ dwarf_find_debug_frame (int found, unw_dyn_info_t *di_debug, unw_word_t ip,
   di->format = UNW_INFO_FORMAT_TABLE;
   di->start_ip = fdesc->start;
   di->end_ip = fdesc->end;
-  di->load_offset = fdesc->load_offset;
   di->u.ti.name_ptr = (unw_word_t) (uintptr_t) obj_name;
   di->u.ti.table_data = (unw_word_t *) fdesc;
   di->u.ti.table_len = sizeof (*fdesc) / sizeof (unw_word_t);
@@ -957,14 +936,12 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
     ip_base = segbase;
   }
 
-  Debug (6, "lookup IP 0x%lx\n", (long) (ip - ip_base - di->load_offset));
-
 #ifndef UNW_REMOTE_ONLY
   if (as == unw_local_addr_space)
     {
-      e = lookup (table, table_len, ip - ip_base - di->load_offset);
+      e = lookup (table, table_len, ip - ip_base);
       if (e && &e[1] < &table[table_len / sizeof (struct table_entry)])
-	last_ip = e[1].start_ip_offset + ip_base + di->load_offset;
+	last_ip = e[1].start_ip_offset + ip_base;
       else
 	last_ip = di->end_ip;
     }
@@ -972,7 +949,7 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
 #endif
     {
 #ifndef UNW_LOCAL_ONLY
-      int32_t last_ip_offset = (int32_t) (di->end_ip - ip_base - di->load_offset);
+      int32_t last_ip_offset = (int32_t) (di->end_ip - ip_base);
       segbase = di->u.rti.segbase;
       if ((ret = remote_lookup (as, (uintptr_t) table, table_len,
                                 (int32_t) (ip - ip_base), &ent, &last_ip_offset, arg)) < 0)
@@ -980,7 +957,7 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
       if (ret)
 	{
 	  e = &ent;
-	  last_ip = last_ip_offset + ip_base + di->load_offset;
+	  last_ip = last_ip_offset + ip_base;
 	}
       else
         e = NULL;       /* no info found */
@@ -994,8 +971,8 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
          unwind info.  */
       return -UNW_ENOINFO;
     }
-  Debug (15, "ip=0x%lx, load_offset=0x%lx, start_ip=0x%lx\n",
-         (long) ip, (long) di->load_offset, (long) (e->start_ip_offset));
+  Debug (15, "ip=0x%lx, start_ip=0x%lx\n",
+         (long) ip, (long) (e->start_ip_offset));
   if (debug_frame_base)
     fde_addr = e->fde_offset + debug_frame_base;
   else
@@ -1019,9 +996,6 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
       pi->flags = UNW_PI_FLAG_DEBUG_FRAME;
     }
 
-  pi->start_ip += di->load_offset;
-  pi->end_ip += di->load_offset;
-
 #if defined(NEED_LAST_IP)
   pi->last_ip = last_ip;
 #else

src/dwarf/Gfind_unwind_table.c

@@ -206,7 +206,6 @@ dwarf_find_unwind_table (struct elf_dyn_info *edi,
 
       edi->di_cache.start_ip = start_ip;
       edi->di_cache.end_ip = end_ip;
-      edi->di_cache.load_offset = 0;
       edi->di_cache.format = UNW_INFO_FORMAT_REMOTE_TABLE;
       edi->di_cache.u.rti.name_ptr = 0;
       /* two 32-bit values (ip_offset/fde_offset) per table-entry: */