[PATCH 4/9] [libbacktrace] Handle DW_FORM_GNU_strp_alt

[Tom de Vries <tdevries@suse.de>]

Handle DW_FORM_GNU_strp_alt which references the .debug_str section in the
.gnu_debugaltlink file.

2018-11-11  Tom de Vries  <tdevries@suse.de>

	* dwarf.c (read_attribute): Handle DW_FORM_GNU_strp_alt
	using altlink.
---
 libbacktrace/dwarf.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/libbacktrace/dwarf.c b/libbacktrace/dwarf.c
index 8b802a085ca..341b84605c0 100644
--- a/libbacktrace/dwarf.c
+++ b/libbacktrace/dwarf.c
@@ -843,14 +843,23 @@ read_attribute (enum dwarf_form form, struct dwarf_buf *buf,
       val->encoding = ATTR_VAL_REF_SECTION;
       return 1;
     case DW_FORM_GNU_strp_alt:
-      val->u.uint = read_offset (buf, is_dwarf64);
-      if (altlink == NULL)
-	{
-	  val->encoding = ATTR_VAL_NONE;
-	  return 1;
-	}
-      val->encoding = ATTR_VAL_REF_SECTION;
-      return 1;
+      {
+	uint64_t offset;
+	offset = read_offset (buf, is_dwarf64);
+	if (altlink == NULL)
+	  {
+	    val->encoding = ATTR_VAL_NONE;
+	    return 1;
+	  }
+	if (offset >= altlink->dwarf_str_size)
+	  {
+	    dwarf_buf_error (buf, "DW_FORM_GNU_strp_alt out of range");
+	    return 0;
+	  }
+	val->encoding = ATTR_VAL_STRING;
+	val->u.string = (const char *) altlink->dwarf_str + offset;
+	return 1;
+      }
     default:
       dwarf_buf_error (buf, "unrecognized DWARF form");
       return 0;
-- 
2.16.4