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Re: ELF bugfixes

From: phcoder
Subject: Re: ELF bugfixes
Date: Fri, 13 Mar 2009 21:41:42 +0100
User-agent: Thunderbird (X11/20090105)

Robert Millan wrote:
On Wed, Mar 11, 2009 at 10:21:41PM +0100, phcoder wrote:
Robert Millan wrote:
On Mon, Mar 02, 2009 at 01:35:06AM +0100, phcoder wrote:
+       * include/grub/elf.h: added missing attributes
This should be a bit more descriptive.

   for (i = 0; i < ehdr->e_phnum; i++)
     if (phdr(i)->p_type == PT_LOAD && phdr(i)->p_filesz != 0)
-       if (phdr(i)->p_paddr < phdr(lowest_segment)->p_paddr)
+ if (lowest_segment == -1 + || phdr(i)->p_paddr < phdr(lowest_segment)->p_paddr)
          lowest_segment = i;
-       if (phdr(i)->p_paddr > phdr(highest_segment)->p_paddr)
+       if (highest_segment == -1
+           || phdr(i)->p_paddr > phdr(highest_segment)->p_paddr)
          highest_segment = i;
Because if first segment doesn't have the PT_LOAD attribute set then it should be considered in this comparison

But you didn't remove the PT_LOAD check.  And in the routine below that
does the actual segment load, we still check for PT_LOAD.  Those should be
consistent, right?

No I expressed myself badly. Original code assumed that first segment has PT_LOAD always set (lowest_segment is 0 initally). I removed this assumption

-  grub_multiboot_payload_entry_offset = ehdr->e_entry - 
+  grub_multiboot_payload_entry_offset = ehdr->e_entry - 
Are you sure about this?  IIRC e_entry is in the virtual address space.  I
think we had some trouble with this (with NetBSD?), which lead to the current
use of p_vaddr in this line.

Actually now thinking I see that the problem is more deep. The section which is loaded at the lowest address isn't necessarily the section which contains entry point. I'll fix this part cleanly and will resubmit the patch

No, but AFAICT the entry point is defined relative to that address, regardless
of which segment contains it.

Actually our segment table is also our table for transforming between virtual and physical address. I don't see why entry point would be defined against virtual address of lowest physical segement


Vladimir 'phcoder' Serbinenko

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