[lldb-dev] Patch to support ELF coredumps

[Samuel Jacob]

>Each object file format, like ELF, should know how the registers contexts
for core files are saved and should be able to reproduce a register context
for a thread. So I would modify ObjectFileELF to contain a virtual
>instance of:
ELF core file's register arrangement is depends on OS, so defining it
ObjectFileELF
has the same problem.

>From quick look at the code, modifying
"source/Plugins/Process/POSIX/RegisterContext_x86_64.cpp" to have both
FreeBSD and Linux RegiserInfo structures should solve this.
However this modification would touch lot of places and I prefer this
modification go as separate patch.

Another approach is copying RegisterContext_x86_64.cpp:g_register_infos and
related macros to elf-core plugin but I dont want to go in this route.

So if you agree I will modify the current patch to include elf-core plugin
only on Linux and FreeBSD platform.
In the 2nd phase I will send patch to include elf-core in all platforms by
modifying "POSIX/RegisterContext_x86_64.cpp".

Thanks
Samuel



On Mon, Feb 25, 2013 at 12:13 PM, Greg Clayton <gclayton at apple.com> wrote:

> That is great that this works, but this doesn't compile on MacOSX. The
> main issue is that in RegisterContext_x86_64.h you are conditionally
> compiling in the GPR structure definition with:
>
> #ifdef __FreeBSD__
> #include "Plugins/Process/FreeBSD/RegisterContextFreeBSD_x86_64.h"
> #endif
>
> #ifdef __linux__
> #include "Plugins/Process/Linux/RegisterContextLinux_x86_64.h"
> #endif
>
> This ELF core plug-in should not be tied to the system on which it is
> compiled. We will need to make it more flexible so it can handle a core
> from either system.
>
> The Mach Core plug-in makes the ObjectFileMachO produce the thread
> register context in:
>
> lldb::RegisterContextSP
> ThreadMachCore::CreateRegisterContextForFrame (StackFrame *frame)
> {
>     lldb::RegisterContextSP reg_ctx_sp;
>     uint32_t concrete_frame_idx = 0;
>
>     if (frame)
>         concrete_frame_idx = frame->GetConcreteFrameIndex ();
>
>     if (concrete_frame_idx == 0)
>     {
>         if (!m_thread_reg_ctx_sp)
>         {
>             ProcessSP process_sp (GetProcess());
>
>             ObjectFile *core_objfile = static_cast<ProcessMachCore
> *>(process_sp.get())->GetCoreObjectFile ();
>             if (core_objfile)
>                 m_thread_reg_ctx_sp =
> core_objfile->GetThreadContextAtIndex (GetID(), *this);
>         }
>         reg_ctx_sp = m_thread_reg_ctx_sp;
>     }
>     else if (m_unwinder_ap.get())
>     {
>         reg_ctx_sp = m_unwinder_ap->CreateRegisterContextForFrame (frame);
>     }
>     return reg_ctx_sp;
> }
>
> Note that at frame zero (concrete_frame_idx == 0) it asks the object file
> create the registers with: GetThreadContextAtIndex().
>
> Each object file format, like ELF, should know how the registers contexts
> for core files are saved and should be able to reproduce a register context
> for a thread. So I would modify ObjectFileELF to contain a virtual instance
> of:
>
> lldb::RegisterContextSP
> ObjectFileELF::CreateRegisterContextForFrame (StackFrame *frame);
>
>
>
>
> On Feb 24, 2013, at 6:37 AM, Samuel Jacob <samueldotj at gmail.com> wrote:
>
> > Hi,
> >
> > I herewith attached a patch to support ELF coredumps.
> > Currently it works for Linux X86-64 core files.
> > Please commit it.
> >
> > Here is the output of a test program
> >
> > $Debug+Asserts/bin/lldb ~/test/a.out -c ~/test/core
> > Core file '/mts/home3/jacobs/test/core' (x86_64) was loaded.
> > Process 0 stopped
> > * thread #1: tid = 0x0000, 0x00000000004004c4 a.out`function4(arg=0) +
> 16 at test.c:4, stop reason = signal SIGSEGV
> >     frame #0: 0x00000000004004c4 a.out`function4(arg=0) + 16 at test.c:4
> >    1    void function4(unsigned int arg)
> >    2    {
> >    3        char *local = 0;
> > -> 4        *local = 0;
> >    5    }
> >    6    void function3()
> >    7    {
> > bt
> > * thread #1: tid = 0x0000, 0x00000000004004c4 a.out`function4(arg=0) +
> 16 at test.c:4, stop reason = signal SIGSEGV
> >     frame #0: 0x00000000004004c4 a.out`function4(arg=0) + 16 at test.c:4
> >     frame #1: 0x00000000004004d7 a.out`function3 + 11 at test.c:8
> >     frame #2: 0x00000000004004e7 a.out`function2(arg=4195559) + 11 at
> test.c:11
> >     frame #3: 0x00000000004004f7 a.out`function1(arg1=0,
> arg2=140736328348032, str=0x00000000004004e7) + 3 at test.c:15
> >     frame #4: 0x0000000000400507 a.out`function1(arg1=0,
> arg2=140736328348048, str=0x00000000004004f7) + 19 at test.c:15
> >     frame #5: 0x00007fbcdfe6c76d libc.so.6`__libc_start_main + 237
> >     frame #6: 0x00000000004003f9 a.out`_start + 41
> >
> > The following may be used as commit log:
> >
> > Added Process plugin to support ELF coredump files.
> > Added member functions in ObjectFileELF to access segment headers and
> data.
> > Modified POSIX dynamic loader plugin to get AUXV data from core files if
> core-file is used.
> > Modified Linux Process plugin so that it will skip handling core
> files(CanDebug()).
> >
> > Regards,
> > Samuel
> > <elf-core.diff>
>
>
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