[llvm-commits] ARM ELF disassembly with integrated-as

[Jan Voung]

Oops forgot to reply-all originally.  +list now.


On Thu, Oct 18, 2012 at 11:46 AM, Greg Fitzgerald <gregf at codeaurora.org>wrote:

> Jan,****
>
> ** **
>
> Thanks so much for the review.****
>
> ** **
>
> > Does this patch handle switching between ARM and thumb code?  E.g., from
> the llvm test "test/MC/ARM/mode-switch.s"****
>
> ** **
>
> No, afraid not.  Is there a concept of switching between ARM and Thumb
> within LLVM?  As I understand, the triple forces it one way or the other.
> Regarding that usage within an assembly file, LLVM currently doesn’t
> support ARM assembly files targeting ELF, only MachO.  If possible, I’d
> prefer not to piggyback that feature on this patch, and then address it at
> the time we add support for parsing ARM ELF assembly (for example, parsing
> the .eabi_attribute directive).****
>
> **
>

I thought there was a concept of switching, based on what
"test/MC/ARM/mode-switch.s" does. The CHECKs in the test are the same with
both the arm and thumb triples.


> **
>
> > Do you have a specific test that the mapping symbols really do get
> emitted, with the right type, binding, etc.?  Perhaps the test should also
> show that it handles switching between $a, $d, and $t, and squashes
> duplicates as you had checks for "AlreadySetData", etc.****
>
> ** **
>
> Not yet.  That’d be a good addition.   And right, a test that also
> demonstrates why AlreadySetData needs to be there would be good.  As it
> turns out, only one of those is really needed, and the others are there to
> claim the functions are idempotent.****
>
> ** **
>
> > One suggestion: In 2010-11-30-reloc-movt.ll, where the symbols have
> shifted, it might be more obvious that the change is correct if it had also
> "OBJ" check for a "Symbol 12", with a "OBJ-NEXT" for foo, or bar, whatever
> it was looking for, similar to what is done in "elf-reloc-01.ll".****
>
> ** **
>
> Good tip, I’ll do that.****
>
> ** **
>
> Thanks,****
>
> Greg****
>
> ** **
>
> ** **
>
> *From:* jvoung at google.com [mailto:jvoung at google.com] *On Behalf Of *Jan
> Voung
> *Sent:* Wednesday, October 17, 2012 10:23 PM
> *To:* Greg Fitzgerald
> *Subject:* Re: [llvm-commits] ARM ELF disassembly with integrated-as****
>
> ** **
>
> Hi Greg,****
>
> ** **
>
> Thanks for working on this!****
>
> ** **
>
> ** **
>
> Two questions:****
>
> (1) Does this patch handle switching between ARM and thumb code?  E.g.,
> from the llvm test "test/MC/ARM/mode-switch.s"****
>
> ** **
>
> (2) Do you have a specific test that the mapping symbols really do get
> emitted, with the right type, binding, etc.?  Perhaps the test should also
> show that it handles switching between $a, $d, and $t, and squashes
> duplicates as you had checks for "AlreadySetData", etc.****
>
> ** **
>
> ** **
>
> One suggestion: In 2010-11-30-reloc-movt.ll, where the symbols have
> shifted, it might be more obvious that the change is correct if it had also
> "OBJ" check for a "Symbol 12", with a "OBJ-NEXT" for foo, or bar, whatever
> it was looking for, similar to what is done in "elf-reloc-01.ll".****
>
> ** **
>
> - Jan****
>
> ** **
>
> On Wed, Oct 17, 2012 at 8:20 PM, Greg Fitzgerald <gregf at codeaurora.org>
> wrote:****
>
> > [LLVMdev] R_ARM_ABS32 disassembly with integrated-as
>
> Please review the attached patch.
>
> Highlights:
> * LLVM now emits an ARM ELF with the same mapping symbols as GCC
> * Because of that, you can now objdump ARM ELF files and not see gibberish
> code where jump tables are stored
> * And having those symbols alleviates concerns Tim mentioned regarding
> linking.
>
> Lowlights:
> * Had the choice of either dumping ARMELFStreamer into the MC layer, or
> pulling MCELFStreamer into the public include directory (for MC).  I chose
> the latter.  It seems quite a bit cleaner, but at the expense of maybe
> exposing an object that might not be ready to move out of its anonymous
> namespace.
> * Needed to update a few somewhat-unrelated unit tests.  Mostly just
> updating references in the symbol table to account for the 3 mapping
> symbols
> at the start of each file (.text=$a, .data=$d, .bss=$d).  These are
> probably
> worth the most scrutiny.
>
> Thanks,
> Greg
>
> ---
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
>
>
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>
> ** **
>
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