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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: Wed, 2 Jul 2014 16:57:03 +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>
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