Re: [PATCH] Explicitly get .dynamic section for "readelf -d"

[Jie Zhang <zhangjie at magima dot com dot cn>]

Nick Clifton wrote:
> There is a small problem with it - it contains duplicated code.  I think 
> that a better approach would be to put the scan for the .dynamic section 
> into the code in process_program_headers() where dynamic_addr and 
> dynamic_size are currently initialised.  Could you try this out please ?

Here is it. But I'm afraid it is not good enough yet.

The -d option of readelf is for displaying the contents of the file's 
dynamic section as stated in the document. However, almost all relevant 
code say dynamic *segment* rather than dynamic *section*. For most 
targets dynamic segment contains only .dynamic section and they are 
equivalent, but for SGI's MIPS this is not true. Is it worth changing 
all "dynamic segment" to "dynamic section", e.g. process_dynamic_segment 
to process_dynamic_section and dynamic_segment to dynamic_section?

The .dynamic section, I think now, should be the first section in the 
dynamic segment. Since section header table is optional in executable 
file, we cannot always rely on it to relocate .dynamic section. If a 
script does not make it come first in the segment, it's the script's 
fault not others. So I think that it would better to make ld warn (or 
error) if the .dynamic section is not the first section in the dynamic 
segment. Is this reasonable? Is there any target other than MIPS that 
has more than one section in dynamic segment? If it is the only target, 
I'm going to add check in _bfd_mips_elf_modify_segment_map (). 
Otherwise, I'm going to add check in map_sections_to_segments (). Are 
they the right places?



--
Jie

2004-06-14  Jie Zhang  <zhangjie@magima.com.cn>

        * binutils/readelf.c (process_program_headers): Better locate .dynamic section.

--- binutils-040601.old/binutils/readelf.c	2004-05-29 08:12:03.000000000 +0800
+++ binutils-040601/binutils/readelf.c	2004-06-14 15:09:01.000000000 +0800
@@ -3147,8 +3147,41 @@ process_program_headers (FILE *file)
 	  if (dynamic_addr)
 	    error (_("more than one dynamic segment\n"));
 
-	  dynamic_addr = segment->p_offset;
-	  dynamic_size = segment->p_filesz;
+	  /* Try to locate the .dynamic section. If there is section header
+             table, we can easily locate it. */
+          if (section_headers != NULL)
+            {
+              Elf_Internal_Shdr *sec;
+              unsigned int j;
+
+              for (j = 0, sec = section_headers;
+                   j < elf_header.e_shnum;
+                   j++, sec++)
+                if (strcmp (SECTION_NAME (sec), ".dynamic") == 0)
+                  break;
+
+              if (j == elf_header.e_shnum || sec->sh_size == 0)
+                {
+                  error (_("no .dynamic section in the dynamic segment"));
+                  break;
+                }
+
+              dynamic_addr = sec->sh_offset;
+              dynamic_size = sec->sh_size;
+
+              if (dynamic_addr < segment->p_offset
+                  || dynamic_addr > segment->p_offset + segment->p_filesz)
+                warn (_("the .dynamic section is not in the dynamic segment"));
+              else if (dynamic_addr > segment->p_offset)
+                warn (_("the .dynamic section is not the first section in the dynamic segment."));
+            }
+          /* Otherwise, we can only assume that the .dynamic section is the
+             first section in the DYNAMIC segment. */
+          else
+            {
+              dynamic_addr = segment->p_offset;
+              dynamic_size = segment->p_filesz;
+            }
 	  break;
 
 	case PT_INTERP: