Gdb support for Debugging Arm M profile with Xilinx Qemu

[sanjana gogte <sanj27272@gmail.com>]

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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

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