Fix unwinding of pre-linked libraries

Prelinker updates section .eh_frame but does not change section .debug_frame.
Libunwind can work with prelinked .eh_frame, but if fails to find call frame
info in unmodified .debug_frame because it does not add the load offset.

ELF load offset from PT_LOAD p_vaddr has to be used to correctly interpret
addresses in the .debug_frame section.

Signed-off-by: Mikhail Durnev <mikhail_durnev@mentor.com>

2 files changed, 35 insertions, 8 deletions

diff --git a/src/dwarf/Gfind_proc_info-lsb.c b/src/dwarf/Gfind_proc_info-lsb.c
index 6519740e..1311d9ab 100644
--- a/src/dwarf/Gfind_proc_info-lsb.c
+++ b/src/dwarf/Gfind_proc_info-lsb.c
@@ -107,13 +107,17 @@ 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)
+load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local, unw_word_t *load_offset)
 {
   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_debuglink) (file, &ei, is_local);
   if (ret != 0)
@@ -173,6 +177,20 @@ load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local)
 #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;
+      }
+
   munmap(ei.image, ei.size);
   return 0;
 }
@@ -225,6 +243,7 @@ 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.  */
 
@@ -251,7 +270,7 @@ 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);
+  err = load_debug_frame (name, &buf, &bufsize, as == unw_local_addr_space, &load_offset);
 
   if (!err)
     {
@@ -259,6 +278,7 @@ 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;
@@ -454,6 +474,7 @@ 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);
@@ -916,12 +937,14 @@ 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);
+      e = lookup (table, table_len, ip - ip_base - di->load_offset);
       if (e && &e[1] < &table[table_len])
-	last_ip = e[1].start_ip_offset + ip_base;
+	last_ip = e[1].start_ip_offset + ip_base + di->load_offset;
       else
 	last_ip = di->end_ip;
     }
@@ -929,7 +952,7 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
 #endif
     {
 #ifndef UNW_LOCAL_ONLY
-      int32_t last_ip_offset = di->end_ip - ip_base;
+      int32_t last_ip_offset = di->end_ip - ip_base - di->load_offset;
       segbase = di->u.rti.segbase;
       if ((ret = remote_lookup (as, (uintptr_t) table, table_len,
                                 ip - ip_base, &ent, &last_ip_offset, arg)) < 0)
@@ -937,7 +960,7 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
       if (ret)
 	{
 	  e = &ent;
-	  last_ip = last_ip_offset + ip_base;
+	  last_ip = last_ip_offset + ip_base + di->load_offset;
 	}
       else
         e = NULL;       /* no info found */
@@ -951,8 +974,8 @@ dwarf_search_unwind_table (unw_addr_space_t as, unw_word_t ip,
          unwind info.  */
       return -UNW_ENOINFO;
     }
-  Debug (15, "ip=0x%lx, start_ip=0x%lx\n",
-         (long) ip, (long) (e->start_ip_offset));
+  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));
   if (debug_frame_base)
     fde_addr = e->fde_offset + debug_frame_base;
   else
@@ -976,6 +999,9 @@ 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
diff --git a/src/dwarf/Gfind_unwind_table.c b/src/dwarf/Gfind_unwind_table.c
index f5f7ad06..a6198ad2 100644
--- a/src/dwarf/Gfind_unwind_table.c
+++ b/src/dwarf/Gfind_unwind_table.c
@@ -193,6 +193,7 @@ dwarf_find_unwind_table (struct elf_dyn_info *edi, unw_addr_space_t as,
 
       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: */