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

Matthew Gardiner mg11 at csr.com
Thu Jul 10 23:13:56 PDT 2014

Todd Fiala wrote:
> > 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.
Thanks, that could be useful. One of the things I need to do with 
PlatformKalimba is enable the "platform process" command pull back data 
about remote targets. This type of data would assist me in supplying 
non-intrusive debug of the kalimbas . Greg floated an idea where I think 
could use platform process/list/info to get data which may include the 
run state of connected (by SPI wire) kalimbas. Firstly "list" connected 
devices, "PID" being virtual since kailmba (currently) runs no OS:

(lldb) platform process list
PID    PARENT USER       ARCH                  NAME
====== ====== ========== ===================== ============================
1                        kalimba-csr-unknown   kal4 (1 core)
2                        kalimba-csr-unknown   kal4 (1 core)

Then we could determine whether the chip is running first, before doing 
any such *intrusive classic gdb-remote* style (which always forces the 
target to stop). Appreciate I may need additional GDB-RSP message to 
achieve this...

(lldb) platform process info 1
Process information for process 1:

Do you think your PlatformLinux stuff may have some code I can copy 
which may help with this area?

> > 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.
I've just had a quick look. It looks to me like...

1. PlatformLinux::ResolveExecutable determines if exe is loadable on the 
error = ModuleList::GetSharedModule (module_spec, exe_module_sp,

but even if error==success, it inspects the exe_module_sp (output by above)
if (!exe_module_sp || exe_module_sp->GetObjectFile() == NULL)

to see, if the GetObjectFile is valid. (If it's NULL ResExec then *fails*).

2. But Module::GetObjectFile() then calls ObjectFileELF::GetArchitecture,
passing it's ArchSpec as a non-const ref.

3.  ObjectFileELF::GetArchitecture then calls ParseSectionHeaders
which mutes the spec.

So, with my limited architectural knowledge of lldb, I think another 
possible fix would be to change ObjectFileELF::GetArchitecture so that 
it does not call ParseSectionHeaders if m_section_headers is non-empty. 
This, at least, prevent the static function (GSHI) being called again.

> 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 :-)
Ok, thanks.


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