[Bug gdb/26876] New: gdb error: internal-error: Unknown CFA rule when debugging the linux kernel with qemu

["robert at robertbuhren dot de" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26876

            Bug ID: 26876
           Summary: gdb error: internal-error: Unknown CFA rule when
                    debugging the linux kernel with qemu
           Product: gdb
           Version: 10.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: robert at robertbuhren dot de
  Target Milestone: ---

Created attachment 12952
  --> https://sourceware.org/bugzilla/attachment.cgi?id=12952&action=edit
linux kernel config

Hi all,

I'm trying to debug a linux kernel issue using gdb. I'm essentially following
this tutorial:
https://www.kernel.org/doc/html/v5.9/dev-tools/gdb-kernel-debugging.html

When I execute "lx-symbols", I get the error mentioned in the header.

I'm using GNU gdb (GDB) 10.1 on archlinux with gcc version 10.2.0 (GCC) and
QEMU emulator version 5.1.0

I have attached the kernel config. The binary exceeds the upload limit. I can
provide it upon request.
The kernel is based on commit: 9ff9b0d392ea08090cd1780fb196f36dbb586529

Here's the exact output of my gdb debugging session:

[I] ~/S/R/S/linux (master|…) $ gdb vmlinux                                     
GNU gdb (GDB) 10.1                                                             
Copyright (C) 2020 Free Software Foundation, Inc.                            
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.              
There is NO WARRANTY, to the extent permitted by law.                           
Type "show copying" and "show warranty" for details.           
This GDB was configured as "x86_64-pc-linux-gnu".                               
Type "show configuration" for configuration details.                            
For bug reporting instructions, please see:                                     
<https://www.gnu.org/software/gdb/bugs/>.                       
Find the GDB manual and other documentation resources online at:                
    <http://www.gnu.org/software/gdb/documentation/>.                           

For help, type "help".                                                         
Type "apropos word" to search for commands related to "word"...                
Reading symbols from vmlinux...        
(gdb) tar rem :1234                            
Remote debugging using :1234                                                    
0x000000000000fff0 in exception_stacks ()                                      
(gdb) c                                                                        
Continuing.                                                                    
^C                                                                              
Program received signal SIGINT, Interrupt.                                      
default_idle () at arch/x86/kernel/process.c:688                                
688             safe_halt();                                                   
(gdb) lx-symbols                                                               
loading vmlinux                                                                 
scanning for modules in /home/robert/Sec-T/Research/SEV-dev-fuzz/linux
../../gdb/dwarf2/frame.c:1085: internal-error: Unknown CFA rule.
A problem internal to GDB has been detected,                                    
further debugging may prove unreliable.
Quit this debugging session? (y or n) y                                        

This is a bug, please report it.  For instructions, see:                        
<https://www.gnu.org/software/gdb/bugs/>.                                       

../../gdb/dwarf2/frame.c:1085: internal-error: Unknown CFA rule.                
A problem internal to GDB has been detected,                                    
further debugging may prove unreliable.        
Create a core file of GDB? (y or n) y                                           
fish: “gdb vmlinux” terminated by signal SIGABRT (Abort)

I'm happy to provide additional details if needed.

Regards,

Robert

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