<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
On 11.05.2012 07:16, Rafael Espíndola wrote:
<blockquote
cite="mid:CAG3jReKU1egh4YW8EyArSAOYbuU00_sw9X=SgLoJsXwPMWePiA@mail.gmail.com"
type="cite">
<blockquote type="cite">
<pre wrap="">But, I found that I can workaround this error by avoiding creating
.group section in object files:
$ elfdump -g a.o
Group Section: .group
index flags / section signature symbol
[0] [ COMDAT ] _Z3barIiEiT_
[1] .text._Z3barIiEiT_ [6]
This group contains only one section, is it really needed?
GCC (4.5.1, 4.7.0) doesn't create one.
Sun C++ 5.11 creates group with 2 sections: bar<int>() text and relocs.
</pre>
</blockquote>
<pre wrap="">
gcc 4.6 on linux produces an output very similar to what clang does.
The groups (comdats) are a generic way to let the linker discard
sections very quickly. In this case it is used for discarding a
method instantiated in two files.</pre>
</blockquote>
<br>
But then it makes sense to put relocs against this section in the
same group also so they can be discarded together (as Sun C++ does).<br>
<br>
The problem is that discarded section is referenced from the section
outside of the discarded group (.rela.eh_frame) via discarded
section symbol.<br>
<br>
If I understand correctly wording of ELF std this is not allowed:<br>
(<a class="moz-txt-link-freetext" href="http://www.sco.com/developers/gabi/latest/ch4.sheader.html#section_groups">http://www.sco.com/developers/gabi/latest/ch4.sheader.html#section_groups</a>)<br>
<br>
<blockquote type="cite">A symbol table entry with <code>STB_LOCAL</code>
binding
that is defined relative to one of a group's sections,
and that is contained in a symbol table section
that is not part of the group,
must be discarded if the group members are discarded.
References to this symbol table entry from outside the group are
not allowed.
</blockquote>
<br>
And here this discarded symbol is referenced via relocation against
.eh_frame section.<br>
<br>
$ ld -r -o all.o a.o b.o<br>
ld: fatal: relocation error: R_386_32: file b.o: section
[10].rel.eh_frame: symbol .text._Z3barIiEiT_ (section): symbol has
been discarded with discarded section: [6].text._Z3barIiEiT_<br>
<br>
<blockquote
cite="mid:CAG3jReKU1egh4YW8EyArSAOYbuU00_sw9X=SgLoJsXwPMWePiA@mail.gmail.com"
type="cite">
<pre wrap="">Just dropping the group would probably create an executable with two
copies of the method. Is that what you get?</pre>
</blockquote>
Yes, this is exactly what I get. But at least I can link :)<br>
</body>
</html>