Gdb support for Debugging Arm M profile with Xilinx Qemu

[sanjana gogte]

Greetings,

I am currently engaged in a project that involves emulating the LM3S811EVB ( M3 Core ) board using Xilinx QEMU (version 7.1.0) . While the emulation process is successful, I am encountering difficulties in attaching GNU Debugger (GDB) or GDB-multiarch to the ELF file being executed on the emulated board. Interestingly, this issue does not arise when utilizing the standard QEMU (version 8.1.5), where I am able to attach GDB and step through the ELF file without any hindrances.

To address this issue, I have experimented with different versions of GDB, specifically:

GNU gdb (Arm GNU Toolchain 13.2.rel1 (Build arm-13.7)) ( arm-none-eabi)

GNU gdb (Linaro_GDB-2019.12) 8.3.1.20191204-git

Error I am facing :

Remote debugging using localhost:1234

Remote 'g' packet reply is too long (expected 68 bytes, got 92 bytes): 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000028100020ffffffff0800000000000041000000000000000000000000000000000000000000000000

(gdb) b main

Breakpoint 1 at 0xc6: file main2.c, line 69.

(gdb) continue

The program is not being run.

(gdb) run

Don't know how to run. Try "help target".

With Gdb-multiarch (12.1)

gef➤ set architecture armv7

The target architecture is set to "armv7".

gef➤ target remote:1234

Remote debugging using :1234

warning: No executable has been specified and target does not support

determining executable automatically. Try using the "file" command.

Remote 'g' packet reply is too long (expected 68 bytes, got 92 bytes): 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000028100020ffffffff0800000000000041000000000000000000000000000000000000000000000000

gef➤ file kernel2.elf

Reading symbols from kernel2.elf...

gef➤ b main

Breakpoint 1 at 0xc6: file main2.c, line 69.

gef➤ continue

The program is not being run.

gef➤ run

Starting program: /mnt/c/Users/Gogte/Desktop/sanjana_intern_project/Qemu_test/test3/LinkerM3/kernel2.elf

/bin/bash: line 1: /mnt/c/Users/Gogte/Desktop/sanjana_intern_project/Qemu_test/test3/LinkerM3/kernel2.elf: cannot execute binary file: Exec format error

/bin/bash: line 1: /mnt/c/Users/Gogte/Desktop/sanjana_intern_project/Qemu_test/test3/LinkerM3/kernel2.elf: Success

During startup program exited with code 126.

If I do the same with Standard qemu binary the gdb works:

Remote debugging using localhost:1234

start () at startup.s:10

--Type <RET> for more, q to quit, c to continue without paging--c

10 ldr r1, =main

(gdb) b main

Breakpoint 1 at 0xc6: file main2.c, line 69.

(gdb) continue

Continuing.

Breakpoint 1, main () at main2.c:69

69 uart_print("Inside main function");

(gdb)

My project necessitates the use of the Xilinx QEMU binary, specifically to leverage the remote port functionality it offers.

Therefore, I am seeking guidance on which version of GDB should be used, or any specific configurations that might enable successful GDB attachment to the ELF file running on Xilinx QEMU.

Regards,

Sanjana