[lldb-dev] Patch to support ELF coredumps

[Greg Clayton]

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>