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<div class="moz-cite-prefix">Hi,<br>
<br>
The round trip passes just tries to load a *complete* object file
in YAML/Native format back. <br>
<br>
The internal state should be the complete object file in
native/yaml format.<br>
<br>
If some state is not recorded and that is really needed in the
writer, we should add that to the Atom model.<br>
<br>
Shankar Easwaran<br>
<br>
On 2/9/2015 1:29 PM, Rui Ueyama wrote:<br>
</div>
<blockquote
cite="mid:CAJENXgt4Vwn6HtgHp07K2esepPdVZ6kP_YRgzGh-L5PcY5NeYQ@mail.gmail.com"
type="cite">
<pre wrap="">I want to bring this again because I think it's important.
It doesn't make sense to store and load intermediate atoms/references in
the middle of link, is it? Teaching LLD about how to read from YAML or
Native object file is fine, and we probably want to teach LLD about how to
emit a re-linkable object file in YAML or Native file. But the round-trip
tests do more than that, right? The tests require more -- dumping linker
internal state to a file and reading it correctly.
On Mon, Feb 9, 2015 at 4:33 AM, Denis Protivensky <
<a class="moz-txt-link-abbreviated" href="mailto:dprotivensky@accesssoftek.com">dprotivensky@accesssoftek.com</a>> wrote:
</pre>
<blockquote type="cite">
<pre wrap=""> A bit off topic: ARM Group relocations define a logical set of consequent
instructions to be relocated to form one single address. For such
relocations a 1 to 1 relation is also met, so no need of special processing
in applyRelocation.
Concerning native format: it also introduced unneeded code complexity to
me when I wanted to set calculated relocation addend back into the
Reference object in the relocation handler to simplify further processing.
Since it crashed in tests because of native format conversion, I needed to
keep calculated addend to pass it along the handlers instead of just
calling ref.addend().
- Denis.
On 02/08/2015 08:42 PM, Shankar Easwaram <a class="moz-txt-link-rfc2396E" href="mailto:shankarke@gmail.com"><shankarke@gmail.com></a>
<a class="moz-txt-link-rfc2396E" href="mailto:shankarke@gmail.com"><shankarke@gmail.com></a> wrote:
ARM has a concept of Group relocations, which applies relocations
considering them as one set may be we should consider extending apply
relocation. What do you think?
</pre>
<blockquote type="cite">
<pre wrap="">On Feb 8, 2015, at 04:50, Simon Atanasyan <a class="moz-txt-link-rfc2396E" href="mailto:simon@atanasyan.com"><simon@atanasyan.com></a>
</pre>
</blockquote>
<pre wrap=""><a class="moz-txt-link-rfc2396E" href="mailto:simon@atanasyan.com"><simon@atanasyan.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">
Nick,
Right now I try to implement exactly the same approach. I split a
relocation record on up to three separate relocations. But there are
two problems on this way.
The first one is how to represent some additional data provided in the
relocation record. That is why I asked the initial question in this
thread. The current solution is to extend the `Reference` class and
add one more attribute to it.
The second problem is how to handle these three relocations. Now the
`TargetRelocationHandler::applyRelocation()` method called one-by-one
for each reference. That is not applied to the MIPS N64 ABI
relocations. In that case we need to calculate the first one, save the
result, calculate the second one using result from the first step,
repeat that for the third relocations and only at the end check the
final result on overflow and apply it to the location. My current idea
is to allow a target specific code to handle the loop over atom's
references now hardcoded in the `AtomSection<ELFT>::write` method.
</pre>
<blockquote type="cite">
<pre wrap="">On Sun, Feb 8, 2015 at 3:21 AM, Nick Kledzik <a class="moz-txt-link-rfc2396E" href="mailto:kledzik@apple.com"><kledzik@apple.com></a>
</pre>
</blockquote>
</blockquote>
<pre wrap=""><a class="moz-txt-link-rfc2396E" href="mailto:kledzik@apple.com"><kledzik@apple.com></a> wrote:
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">Simon,
Sounds like the instruction relocating is so complicated that ELF
</pre>
</blockquote>
</blockquote>
<pre wrap="">requires up to three relocation records to encode how to fix up one
instruction. If that is the case, why not do the same and have up to three
Reference objects on the same atom offset to record the same info? I
thought that was model that the ELF part of lld was using - there is a
one-to-one mapping of ELF reloc to lld References.
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">
Or am I misunderstanding the issue?
-Nick
</pre>
<blockquote type="cite">
<pre wrap="">On Feb 5, 2015, at 12:22 PM, Simon Atanasyan <a class="moz-txt-link-rfc2396E" href="mailto:simon@atanasyan.com"><simon@atanasyan.com></a>
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap=""><a class="moz-txt-link-rfc2396E" href="mailto:simon@atanasyan.com"><simon@atanasyan.com></a> wrote:
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">Hi,
I need an advice on implementation of a very specific kind of
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">relocations
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">used by MIPS N64 ABI. As usual the main problem is how to pass target
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">specific
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">data over Native/YAML conversion barrier.
In this ABI relocation record r_info field in fact consists of five
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">subfields:
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">* r_sym - symbol index
* r_ssym - special symbol
* r_type3 - third relocation type
* r_type2 - second relocation type
* r_type - first relocation type
Up to three these relocations applied one by one. The first relocation
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">uses
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">an addendum from the relocation record. Each subsequent relocation
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">takes as
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">its addend the result of the previous operation. Only the final
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">operation
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">actually modifies the location relocated. The first relocation uses as
a reference symbol specified by the r_sym field. The third relocation
assumes NULL symbol.
The most interesting case is the second relocation. It uses the special
symbol value given by the r_ssym field. This field can contain four
predefined values:
* RSS_UNDEF - zero value
* RSS_GP - value of gp symbol
* RSS_GP0 - gp0 value taken from the .MIPS.options or .reginfo
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">section
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">* RSS_LOC - address of location being relocated
So the problem is how to store these four constants in the
lld::Reference object.
The RSS_UNDEF is obviously not a problem. To represent the RSS_GP
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">value I can
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">set an AbsoluteAtom created for the "_gp" as the reference's target.
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">But what
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">about RSS_GP0 and RSS_LOC? I am considering the following approaches
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">but cannot
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">select the best one:
a) Create AbsoluteAtom for each of these cases and set them as the
reference's target.
The problem is that these atoms are fake and should not go to the
symbol table.
One more problem is to select unique names for these atoms.
b) Use two high bits of lld::Reference::_kindValue field to encode
RSS_xxx value.
Then decode these bits in the RelocationHandler to calculate result
of relocation.
In that case the problem is how to represent a relocation kind
value in YAML format.
The simple xxxRelocationStringTable::kindStrings[] array will not
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">satisfy us.
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">c) Add one more field to the lld::Reference class. Something like the
DefinedAtom::CodeModel
field.
Any advices, ideas, and/or objections are much appreciated.
--
Simon Atanasyan
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</blockquote>
</blockquote>
<pre wrap="">
--
Simon Atanasyan
</pre>
</blockquote>
<pre wrap="">
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</blockquote>
<pre wrap="">
</pre>
<br>
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation</pre>
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