section.
This helps because in practice sections form a dag with debug sections pointing
to text sections. Finishing up the text sections first makes the debug section
relaxation trivial.
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portion. While the fragment boundary is usually already aligned, it is possible for it not to be, which
would lead to a non-aligned final displacement.
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the MCCodeEmitter, which seems like a better organization.
- Also, cleaned up some magic constants while in the area.
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With this we don't need the EffectiveSize field anymore. Without that field
LayoutFragment only updates offsets and we don't need to invalidate the
current fragment when it is relaxed (only the ones following it).
This is also a very small improvement in the accuracy of the layout info as
we now use the after relaxation size immediately.
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Since we now don't update addresses so early, we might relax a bit more than
we need to. This is simillar to the issue in PR8467.
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the offset. Add a new fixup flag to represent this, and use it for the one fixups that I have a testcase for needing
this. It's quite likely that the other Thumb fixups will need this too, and to have their fixup encoding logic
adjusted accordingly.
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before:
4 assembler - Number of assembler layout and relaxation steps
78563 assembler - Number of emitted assembler fragments
8693904 assembler - Number of emitted object file bytes
271223 assembler - Number of evaluated fixups
330771677 assembler - Number of fragment layouts
5958 assembler - Number of relaxed instructions
2508361 mcexpr - Number of MCExpr evaluations
real 0m26.123s
user 0m25.694s
sys 0m0.388s
after:
4 assembler - Number of assembler layout and relaxation steps
78563 assembler - Number of emitted assembler fragments
8693904 assembler - Number of emitted object file bytes
271223 assembler - Number of evaluated fixups
231507 assembler - Number of fragment layouts
5958 assembler - Number of relaxed instructions
2508361 mcexpr - Number of MCExpr evaluations
real 0m2.500s
user 0m2.113s
sys 0m0.273s
And yes, the outputs are identical :-)
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actuall addresses in a .o file, so it is better to let the MachO writer compute
it.
This is good for two reasons. First, areas that shouldn't care about
addresses now don't have access to it. Second, the layout of each section
is independent. I should use this in a subsequent commit to speed it up.
Most of the patch is just removing the section address computation. The two
interesting parts are the change on how we handle padding in the end
of sections and how MachO can get the address of a-b when a and b are in
different sections.
Since now the expression evaluation normally doesn't know the section address,
it will think that a-b needs relocation and let the MachO writer know. Once
it has computed the section addresses, it calls back the expression evaluation
with the section addresses to resolve these expressions.
The remaining problem is the handling of padding. Currently it will create
a special alignment fragment at the end. Since that fragment doesn't update
the alignment of the section, it needs the real address to be computed.
Since now the layout will not compute a-b with a and b in different sections,
the only effect that the special alignment fragment has is update the
address size of the section. This can also be done by the MachO writer.
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contain only data. Handle them specially instead of using AddSectionToTheEnd.
This moves a hack from the generic assembler to the elf writer. It is also
a bit faster and should make other improvements easier.
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variable if recursing fails to simplify it.
Factor AliasedSymbol to be a method of MCSymbol.
Update MCAssembler::EvaluateFixup to match the change in
EvaluateAsRelocatableImpl.
Remove the WeakRefExpr hack, as the object writer now sees the weakref with
no extra effort needed.
Nothing else is using MCTargetExpr, but keep it for now.
Now that the ELF writer sees relocations with aliases, handle
.weak foo2
foo2:
.weak bar2
.set bar2,foo2
.quad bar2
the same way gas does and produce a relocation with bar2.
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This is really slow with we have 1000s of sections each with a corresponding
relocation section. Also, it is only used by the ELF writer to add
basic data, so there is no need to force a new layout pass.
Should fix PR8563.
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// FIXME: We should compute this sooner, we don't want to recurse here, and
// we would like to be more functional.
In MCAssembler::ComputeFragmentSize.
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and output the dwarf line number tables. This contains the code to emit and
encode the dwarf line tables from the previously gathered information in the
MCLineSection objects. This contains all the details to encode the line and
address deltas into the dwarf line table.
To do this an MCDwarfLineAddrFragment has been added.
Also this moves the interface code out of Mach-O streamer into
MCDwarf so it should be useable by other object file formats.
There is now one call to be made from an MCObjectStreamer
EmitInstruction() method:
MCLineEntry::Make(this, getCurrentSection());
to create a line entry after each instruction is assembled.
And one call call to be made from an MCObjectStreamer Finish() method:
MCDwarfFileTable::Emit(this, DwarfLineSection);
when getContext().hasDwarfFiles() is true and is passed a object file specific
MCSection where to emit the dwarf file and the line tables.
This appears to now be correct for 32-bit targets, at least x86. But the
relocation entries for 64-bit Darwin needs some further work which is next
up to work on. So for now the 64-bit Mach-O target does not output the
dwarf file and line tables.
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resolved or not. Different object files have different restrictions and
different native assemblers have different idiosyncrasies we want to emulate
for now.
Move the existing MachO logic to the new place and implement an ELF one that
gets fixups to globals right.
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The ELF implementation now creates text, data and bss to match the gnu as
behavior.
The text streamer still has the old MachO specific behavior since
the testsuite checks that it will error when a directive is given
before a setting the current section for example.
A nice benefit is that -n is not required anymore when producing
ELF files.
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Introduce a helper method to add a section to the end of a layout. This
will be used by the ELF ObjectWriter code to add the metadata sections
(symbol table, etc) to the end of an object file.
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of manually doing padding/editing layout in LayoutSection().
- This probably seems like six-of-one and half-dozen of another, but there
is a method to my madness.
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be diced into atoms, and adjust getAtom() to take this into account.
- This fixes relocations to symbols in fixed size literal sections, for
example.
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- This eliminates getAtomForAddress() (which was a linear search) and
simplifies getAtom().
- This also fixes some correctness problems where local labels at the same
address as non-local labels could be assigned to the wrong atom.
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exactly two passes in that case, and don't ever need to recompute any layout,
so this is a nice baseline for relaxation performance.
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- Still O(N^2), just a faster form, and now its the MCAsmLayout's fault.
On the .s I am tuning against (combine.s from 403.gcc):
--
ddunbar@lordcrumb:MC$ diff stats-before.txt stats-after.txt
5,10c5,10
< 1728 assembler - Number of assembler layout and relaxation steps
< 7707 assembler - Number of emitted assembler fragments
< 120588 assembler - Number of emitted object file bytes
< 2233448 assembler - Number of evaluated fixups
< 1727 assembler - Number of relaxed instructions
< 6723845 mcexpr - Number of MCExpr evaluations
---
> 3 assembler - Number of assembler layout and relaxation steps
> 7707 assembler - Number of emitted assembler fragments
> 120588 assembler - Number of emitted object file bytes
> 14796 assembler - Number of evaluated fixups
> 1727 assembler - Number of relaxed instructions
> 67889 mcexpr - Number of MCExpr evaluations
--
Feel free to LOL at the -before numbers, if you like.
I am a little surprised we make more than 2 relaxation passes. It's pretty
trivial for us to do relaxation out-of-order if that would give a speedup.
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