<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Mon, Feb 9, 2015 at 12:24 PM, Shankar Easwaran <span dir="ltr"><<a href="mailto:shankare@codeaurora.org" target="_blank">shankare@codeaurora.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div>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></div></div></blockquote><div><br></div><div>Again, not only saying we should do something, but please elaborate why you think we should. Otherwise we can't discuss...</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><div>
Shankar Easwaran<div><div class="h5"><br>
<br>
On 2/9/2015 1:29 PM, Rui Ueyama wrote:<br>
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<blockquote type="cite">
<pre>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 href="mailto:dprotivensky@accesssoftek.com" target="_blank">dprotivensky@accesssoftek.com</a>> wrote:
</pre>
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<pre> 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 href="mailto:shankarke@gmail.com" target="_blank"><shankarke@gmail.com></a>
<a href="mailto:shankarke@gmail.com" target="_blank"><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>On Feb 8, 2015, at 04:50, Simon Atanasyan <a href="mailto:simon@atanasyan.com" target="_blank"><simon@atanasyan.com></a>
</pre>
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<pre><a href="mailto:simon@atanasyan.com" target="_blank"><simon@atanasyan.com></a> wrote:
</pre>
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<pre>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>On Sun, Feb 8, 2015 at 3:21 AM, Nick Kledzik <a href="mailto:kledzik@apple.com" target="_blank"><kledzik@apple.com></a>
</pre>
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<pre><a href="mailto:kledzik@apple.com" target="_blank"><kledzik@apple.com></a> wrote:
</pre>
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<pre>Simon,
Sounds like the instruction relocating is so complicated that ELF
</pre>
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<pre>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>
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<blockquote type="cite">
<pre>Or am I misunderstanding the issue?
-Nick
</pre>
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<pre>On Feb 5, 2015, at 12:22 PM, Simon Atanasyan <a href="mailto:simon@atanasyan.com" target="_blank"><simon@atanasyan.com></a>
</pre>
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<pre><a href="mailto:simon@atanasyan.com" target="_blank"><simon@atanasyan.com></a> wrote:
</pre>
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<pre>Hi,
I need an advice on implementation of a very specific kind of
</pre>
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</blockquote>
</blockquote>
<pre>relocations
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<pre>used by MIPS N64 ABI. As usual the main problem is how to pass target
</pre>
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<pre>specific
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<pre>data over Native/YAML conversion barrier.
In this ABI relocation record r_info field in fact consists of five
</pre>
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<pre>subfields:
</pre>
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<pre>* 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>
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<pre>uses
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<pre>an addendum from the relocation record. Each subsequent relocation
</pre>
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<pre>takes as
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<pre>its addend the result of the previous operation. Only the final
</pre>
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<pre>operation
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<pre>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>
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<pre>section
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<pre>* 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>
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<pre>value I can
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<pre>set an AbsoluteAtom created for the "_gp" as the reference's target.
</pre>
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<pre>But what
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<pre>about RSS_GP0 and RSS_LOC? I am considering the following approaches
</pre>
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<pre>but cannot
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<pre>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>
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<pre>satisfy us.
</pre>
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<pre>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>--
Simon Atanasyan
</pre>
</blockquote>
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</div></div><span class="HOEnZb"><font color="#888888"><pre cols="72">--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation</pre>
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