Re: ELF bugfixes

[phcoder <phcoder@gmail.com>]

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;
>>>>        }
>>> Why?
>> 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 - phdr(lowest_segment)->p_vaddr;
>>>> +  grub_multiboot_payload_entry_offset = ehdr->e_entry - phdr(lowest_segment)->p_paddr;
>>> 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

-- 

Regards
Vladimir 'phcoder' Serbinenko