Re: [gold] Error out when there is an access beyond the end of the merged section

[Alexander Ivchenko <aivchenk at gmail dot com>]

Hi Cary, could you please take a look at the patch.

--Alexander

2014-07-11 14:07 GMT+04:00 Alexander Ivchenko <aivchenk@gmail.com>:
> *kind ping*
>
>
> --Alexander
>
> 2014-07-02 16:57 GMT+04:00 Alexander Ivchenko <aivchenk@gmail.com>:
>> Hi Cary,
>>
>> I think you are right that it would be better to give an error from
>> Merged_symbol_value::value_from_output_section, but I think that just
>> replacing gold_assert is wrong:
>>
>> Here is how "found" is initialized:
>> bool found = object->merge_map()->get_output_offset(NULL, input_shndx,
>>                                                     input_offset,
>>                                                     &output_offset,
>>                                                     object);
>>
>> And Object_merge_map::get_output_offset can return false in three cases:
>>
>> 1)
>>   if (map == NULL
>>       || (merge_map != NULL && map->merge_map != merge_map))
>>     return false;
>>
>> 2)
>>   std::vector<Input_merge_entry>::const_iterator p =
>>     std::lower_bound(map->entries.begin(), map->entries.end(),
>>                      entry, Input_merge_compare());
>>   if (p == map->entries.end() || p->input_offset > input_offset)
>>     {
>>       if (p == map->entries.begin())
>>         return false;
>>       --p;
>>       gold_assert(p->input_offset <= input_offset);
>>     }
>>
>> and
>>
>> 3)
>>   if (input_offset - p->input_offset
>>       >= static_cast<section_offset_type>(p->length))
>>        return false;
>>
>> AFAIU, for cases 1) and 2) the gold_assert in
>> Merged_symbol_value::value_from_output_section should really be hit,
>> and only 3) should give us an error with "access beyond end of merged
>> section".
>>
>> So, I think, we should move gold_assert to 1), 2) in order to catch
>> that situation. Something like that:
>>
>>
>> diff --git a/gold/ChangeLog b/gold/ChangeLog
>> index 264f127..8608aaa 100644
>> --- a/gold/ChangeLog
>> +++ b/gold/ChangeLog
>> @@ -1,3 +1,12 @@
>> +2014-07-02  Alexander Ivchenko  <alexander.ivchenko@intel.com>
>> +
>> + * reloc.cc (Merged_symbol_value<size>::value_from_output_section):
>> + error out (instead of gold_assert) when we see that there is an
>> + access beyond the end of the merged section.
>> + * merge.cc (Object_merge_map::get_output_offset): Add two additional
>> + asserts.
>> + * merge.h (Object_merge_map::get_output_offset): Adjust the comment.
>> +
>>  2014-06-27  Alan Modra  <amodra@gmail.com>
>>
>>   * symtab.cc (Symbol::should_add_dynsym_entry): Don't make inline.
>> diff --git a/gold/merge.cc b/gold/merge.cc
>> index 6d444e6..8c91b20 100644
>> --- a/gold/merge.cc
>> +++ b/gold/merge.cc
>> @@ -148,6 +148,14 @@ Object_merge_map::get_output_offset(const
>> Merge_map* merge_map,
>>      section_offset_type* output_offset)
>>  {
>>    Input_merge_map* map = this->get_input_merge_map(shndx);
>> +
>> +  // If this assertion fails, then it means that we are called from
>> +  // Merged_symbol_value<size>::value_from_output_section and some
>> +  // relocation was against a portion of an input merge section which
>> +  // we didn't map to the output file and we didn't explicitly discard.
>> +  // We should always map all portions of input merge sections.
>> +  gold_assert(merge_map != NULL || map != NULL);
>> +
>>    if (map == NULL
>>        || (merge_map != NULL && map->merge_map != merge_map))
>>      return false;
>> @@ -166,6 +174,11 @@ Object_merge_map::get_output_offset(const
>> Merge_map* merge_map,
>>       entry, Input_merge_compare());
>>    if (p == map->entries.end() || p->input_offset > input_offset)
>>      {
>> +      // Just like in the assert in the beginning of this method: we are
>> +      // called from Merged_symbol_value<size>::value_from_output_section
>> +      // and failed to map some portion of some input merge section.
>> +      gold_assert(merge_map != NULL || p != map->entries.begin());
>> +
>>        if (p == map->entries.begin())
>>   return false;
>>        --p;
>> diff --git a/gold/merge.h b/gold/merge.h
>> index b4fd8e1..ff4f3af 100644
>> --- a/gold/merge.h
>> +++ b/gold/merge.h
>> @@ -61,8 +61,9 @@ class Object_merge_map
>>        section_size_type length, section_offset_type output_offset);
>>
>>    // Get the output offset for an input address.  MERGE_MAP is the map
>> -  // we are looking for, or NULL if we don't care.  The input address
>> -  // is at offset OFFSET in section SHNDX.  This sets *OUTPUT_OFFSET
>> +  // we are looking for, or NULL if we don't care - in this case, we
>> +  // assume that failing to find the output offset is fatal.  The input
>> +  // address is at offset OFFSET in section SHNDX.  This sets *OUTPUT_OFFSET
>>    // to the offset in the output section; this will be -1 if the bytes
>>    // are not being copied to the output.  This returns true if the
>>    // mapping is known, false otherwise.  *OUTPUT_OFFSET is relative to
>> diff --git a/gold/reloc.cc b/gold/reloc.cc
>> index 115ab37..dd86a08 100644
>> --- a/gold/reloc.cc
>> +++ b/gold/reloc.cc
>> @@ -1478,11 +1478,14 @@ Merged_symbol_value<size>::value_from_output_section(
>>        input_offset,
>>        &output_offset);
>>
>> -  // If this assertion fails, it means that some relocation was
>> -  // against a portion of an input merge section which we didn't map
>> -  // to the output file and we didn't explicitly discard.  We should
>> -  // always map all portions of input merge sections.
>> -  gold_assert(found);
>> +  if (!found)
>> +    {
>> +      // FIXME: const_cast is ugly..
>> +      object->error(_("access beyond end of merged section (%s+0x%lx)"),
>> +    const_cast<Relobj*>(object)->section_name(input_shndx).c_str(),
>> +    static_cast<long>(input_offset));
>> +      return 0;
>> +    }
>>
>>    if (output_offset == -1)
>>      return 0;
>>
>>
>>
>> There is an unfortunate necessity of const_cast, if we want to print
>> out the name of the section.
>> What do you think?
>>
>>
>> --Alexander
>>
>> 2014-07-02 0:18 GMT+04:00 Cary Coutant <ccoutant@google.com>:
>>>> +2014-07-01  Alexander Ivchenko  <alexander.ivchenko@intel.com>
>>>> +
>>>> + * merge.cc (Object_merge_map::get_output_offset): error out when we see
>>>> + that there is an access beyond the end of the merged section.
>>>> + * merge.h (Object_merge_map::get_output_offset): Add new argument.
>>>> + (Merge_map::get_output_offset): Adjust
>>>> + Object_merge_map::get_output_offset call with additional argument.
>>>> + * reloc.cc (Merged_symbol_value<size>::value_from_output_section):
>>>> + Ditto.
>>>
>>> I don't think Object_merge_map or Merge_map should be printing this
>>> error. Instead, I'd prefer to issue the error from
>>> Merged_symbol_value::value_from_output_section in place of the
>>> gold_assert. Everything needed to print the error message is readily
>>> available there.
>>>
>>> It would be nice to print the section name as well as the offset. You
>>> should just be able to replace gold_assert with this:
>>>
>>>   if (!found)
>>>     {
>>>       object->error(_("access beyond end of merged section (%s+%ld)"),
>>>                     object->section_name(input_shndx),
>>>                     static_cast<long>(input_offset));
>>>       return 0;
>>>     }
>>>
>>> Thanks for looking at this!
>>>
>>> -cary