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Re: [gold] Error out when there is an access beyond the end of the merged section
- From: Alexander Ivchenko <aivchenk at gmail dot com>
- To: Cary Coutant <ccoutant at google dot com>
- Cc: binutils <binutils at sourceware dot org>
- Date: Fri, 11 Jul 2014 14:07:05 +0400
- Subject: Re: [gold] Error out when there is an access beyond the end of the merged section
- Authentication-results: sourceware.org; auth=none
- References: <CACysShj9wK3e1eC56TffaOQknD4A8XF3NVcyYUNAKEPOux2E8w at mail dot gmail dot com> <CAHACq4rvh5Uv_tXqwgNTrir5zBB_Vi+sO1tYhLYWkWsQdi+-Sg at mail dot gmail dot com> <CACysShgkDLZWzZZtZFwandLGztSTqNkZEniXcyQDWNxE4Cj2Vg at mail dot gmail dot 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