[Lldb-commits] [PATCH] ObjectFileELF::GetSectionHeaderInfo sets arch_spec unnecessarily

[Todd Fiala]

> Please note that I copied a lot of the PlatformLinux code into
PlatformKalimba

Oh shucks, I have a boatload of changes going into PlatformLinux to support
remote debugging!  I've been stuck the last week dealing with testing,
Windows-related builds/issues, and other minutiae but I am looking to
getting back to this.  You can keep your eyes on the changes I check in for
PlatofrmLinux to support llgs.  I'll be refactoring a bunch of code in
PlatformDarwin into PlatformPOSIX, and changing a few more details in
PlatformLinux.

> When I invoke "target create kalimba.elf" I actually see ObjectFileELF::
GetSectionHeaderInfo called *several times* whilst the target is created:

Yeah I have a note to go back to figure out why that's the case.  When I
added the note support, I saw it getting called several times when it seems
like it should have been once.  The ObjectFileELF was getting created and
destroyed multiple times, which I think was unintended.  I'll look closer
into why that's happening.  Thanks for reminding me.

> It would be great if we could prevent the arch_spec being modified again,
after the headers are parsed. Either with my patch or something similar.
Anyway, I'm off now, so I'll catch up sometime tomorrow.

Okay, hopefully by then it will all be better :-)

Thanks,
Todd


On Thu, Jul 10, 2014 at 7:07 AM, Matthew Gardiner <mg11 at csr.com> wrote:

> Todd Fiala wrote:
>
>> I'll have a look later this morning. That code indeed is intended to only
>> be run before they section header parsing. It may have evolved poorly since
>> that was my initial attempt when I thought all of files had the header ABI
>> set correctly.
>>
>> It is still useful as a fallback if the notes are not present.
>>
>> I hadn't yet seen a calling sequence where that static method was called
>> after parsing the section headers but clearly it sounds like you are
>> hitting it.
>>
>
> Hi Todd,
>
> Yup, It would be cool if you could take a look.
>
> When I invoke "target create kalimba.elf" I actually see ObjectFileELF::GetSectionHeaderInfo
> called *several times* whilst the target is created:
>
> The first time...
>
> #0 ObjectFileELF::GetSectionHeaderInfo (section_headers=std::vector of
> length 0, capacity 0, object_data=...,
> #1 ObjectFileELF::GetModuleSpecifications
> #2  lldb_private::ObjectFile::GetModuleSpecifications (overloaded
> function)
> #3  lldb_private::ObjectFile::GetModuleSpecifications
> #4  lldb_private::TargetList::CreateTarget
>
> It is subsequently called again like this:
>
> #0  ObjectFileELF::GetSectionHeaderInfo (section_headers=std::vector of
> length 18,
> #1  ObjectFileELF::ParseSectionHeaders (
> #2  ObjectFileELF::GetArchitecture (
> #3  lldb_private::Module::GetObjectFile (
> #4  lldb_private::ModuleList::GetSharedModule (
> #5  lldb_private::PlatformKalimba::ResolveExecutable (
> #6  lldb_private::TargetList::CreateTarget (
>
> As you can see GSHI gets called again with a non-empty section list when
> the platform tries to resolve the executable.
>
>
> Please note that I copied a lot of the PlatformLinux code into
> PlatformKalimba. So the behaviour I see is not specific to my kalimba
> implementation: loading a linux ELF built for x86_64 execution does the
> same thing:
>
> do:
>
> (lldb) target create ~/src/../simple/i64-hello.elf
>
> with a breakpoint here in ObjectFileELF::GSHI:
>
>     if (!section_headers.empty())
> -->   return section_headers.size();
>
> you'll see this call stack at some stage:
> #0  ObjectFileELF::GetSectionHeaderInfo (section_headers=std::vector of
> length 35
> #1  ObjectFileELF::ParseSectionHeaders (
> #2  ObjectFileELF::GetArchitecture (
> #3  lldb_private::Module::GetObjectFile (
> #4  lldb_private::ModuleList::GetSharedModule (
> #5  lldb_private::PlatformLinux::ResolveExecutable (
> #6  lldb_private::TargetList::CreateTarget (
>
> It would be great if we could prevent the arch_spec being modified again,
> after the headers are parsed. Either with my patch or something similar.
> Anyway, I'm off now, so I'll catch up sometime tomorrow.
>
> thanks
> Matt
>
>
>
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-- 
Todd Fiala | Software Engineer | tfiala at google.com | 650-943-3180
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