[lldb-dev] Linux Core Dump and Symbol resolution

[Samuel Jacob]

Hi,

I am new to lldb and creating a patch to support Linux coredumps.
This plugin is based on mach-core plugin.
Currently it can parse NOTE segments from a elf corefile(x86_64) and loads
all the threads.
ie "thread list" works.

It also reads the PRSTATUS structure and populates the register information.
ie "register read" works fine.

However lldb is not using the symbol files while using the core file.
Because of this it is not using DWARF structures while creating frames.
That is frame variables and arguments are not available. Also lldb not
resolving address to symbols.

$lldb
(lldb) target create -c ./core
Core file '/mts/home3/jacobs/test/core' (x86_64) was loaded.
Process 0 stopped
* thread #1: tid = 0x0000, 0x00000000004004c4, stop reason = signal SIGCONT
    frame #0: 0x00000000004004c4
error: core file does not contain 0x4004c4
(lldb) target modules add ./a.out
(lldb) image lookup --address  0x4004c4
      Address: a.out[0x00000000004004c4] (a.out..text + 244)
      Summary: a.out`function4 + 16 at test.c:4
(lldb) bt
* thread #1: tid = 0x0000, 0x00000000004004c4, stop reason = signal SIGCONT
    frame #0: 0x00000000004004c4
    frame #1: 0x00000000004004d7
    frame #2: 0x00000000004004e7
    frame #3: 0x00000000004004f7
    frame #4: 0x0000000000400507
(lldb) image lookup --address 0x00000000004004d7
      Address: a.out[0x00000000004004d7] (a.out..text + 263)
      Summary: a.out`function3 + 11 at test.c:8

In the above example the IP's are not resolved to symbol in "bt" although
lldb is able to resolve the addresses using "image lookukp" . What command
should be used to link a target with symbol file?

Here is the program that I used which compiled with "gcc -O0 -g3"
$cat test.c
void function4(unsigned int arg)
{
    char *local = 0;
    *local = 0;
}
void function3()
{
    function4(-1);
}
void function2(long arg)
{
    function3();
}
void function1(int arg1, long arg2, char *str)
{
    function2(1);
}
void main()
{
    function1(0, 1L, "Test\n");
}

GDB output

$gdb --quiet a.out core
Reading symbols from /mts/home3/jacobs/test/a.out...done.

warning: exec file is newer than core file.
[New LWP 26718]

warning: Can't read pathname for load map: Input/output error.
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
#0  0x00000000004004c4 in function4 (arg=0) at test.c:4
4           *local = 0;
(gdb) bt
#0  0x00000000004004c4 in function4 (arg=0) at test.c:4
#1  0x00000000004004d7 in function3 () at test.c:8
#2  0x00000000004004e7 in function2 (arg=4195559) at test.c:11
#3  0x00000000004004f7 in function1 (arg1=0, arg2=140736328348032,
str=0x4004e7  <incomplete sequence \370\270>) at test.c:15
#4  0x0000000000400507 in function1 (arg1=0, arg2=140736328348048,
str=0x4004f7 "\345H\203\354\030\211}\374H\211u\360H\211U\350\277\001") at
test.c:15
#5  0x00007fbcdfe6c76d in __libc_start_main () from
/lib/x86_64-linux-gnu/libc.so.6
#6  0x00000000004003f9 in _start ()

I can post the patch if anyone interested(but it needs to be cleaned up).

Thanks
Samuel
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