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

Matthew Gardiner mg11 at csr.com
Thu Jul 10 07:07:15 PDT 2014

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:


(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.


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