Re: ELF bugfixes

[phcoder <phcoder@gmail.com>]

Robert Millan wrote:
> On Sat, Mar 21, 2009 at 06:58:58PM +0100, phcoder wrote:
>> Robert Millan wrote:
>>> On Wed, Mar 18, 2009 at 02:26:40PM +0100, phcoder wrote:
>>>> Robert Millan wrote:
>>>>> On Fri, Mar 13, 2009 at 09:52:39PM +0100, phcoder wrote:
>>>>>> -  grub_multiboot_payload_entry_offset = ehdr->e_entry - phdr(lowest_segment)->p_vaddr;
>>>>>> +  for (i = 0; i < ehdr->e_phnum; i++)
>>>>>> +    if (phdr(i)->p_vaddr <= ehdr->e_entry +	&& phdr(i)->p_vaddr 
>>>>>> + phdr(i)->p_memsz > ehdr->e_entry)
>>>>>> +      grub_multiboot_payload_entry_offset = (ehdr->e_entry - phdr(i)->p_vaddr)
>>>>>> +	+ (phdr(i)->p_paddr  - phdr(lowest_segment)->p_paddr);
>>>>> You need to handle the case in which grub_multiboot_payload_entry_offset is left
>>>>> uninitialized (it needs to be initialized each time the multiboot command is
>>>>> run, not just when the module is loaded).
>>>>>
>>>> module? actually it's when loading image. Perhaps you mean that   
>>>> additional error check is necessary
>>> I meant GRUB's multiboot.mod, not the payload's module.  Sorry I wasn't clear.
>>>
>> With this error check if grub_multiboot_payload_entry_offset it can  
>> happen only if no image is loaded. And actually  
>> grub_multiboot_payload_entry_offset is set to 0 at multiboot.mod load
>> So I don't really understand the problem
> 
> You can't rely on grub_multiboot_payload_entry_offset being set to 0, because
> any subsequent call of "multiboot /something" has the potential to override
> this.  You must not assume the multiboot command is only going to be run once.
> 
No but it always corresponds to the current image. It's set either in 
multiboot.c or in grub_multiboot_load_elf

-- 

Regards
Vladimir 'phcoder' Serbinenko