Hi all, I’m attempting to use gdb to debug over a serial connection using two VM’s. I’m getting a “Permission denied” when I try to connect over the serial com port. Gdb has the following output when I try to connect: Reading symbols from vmlinux... +target remote /dev/ttyS1 Remote debugging using /dev/ttyS1 [remote] start_remote_1: enter [remote] Sending packet: $qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-events+;exec-events+;vContSupported+;QThreadEvents+;no-resumed+;memory-tagging+#ec [remote] Junk: d [remote] Junk: i [remote] Junk: a [remote] Junk: g [remote] Junk: : [remote] Junk: [remote] Received Nak [remote] Sending packet: $qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-events+;exec-events+;vContSupported+;QThreadEvents+;no-resumed+;memory-tagging+#ec [remote] Junk: 2 [remote] Junk: 2 [remote] Junk: : [remote] Junk: [remote] Junk: P [remote] Junk: e [remote] Junk: r [remote] Junk: m [remote] Junk: i [remote] Junk: s [remote] Junk: s [remote] Junk: i [remote] Junk: o [remote] Junk: n [remote] Junk: [remote] Junk: d [remote] Junk: e [remote] Junk: n [remote] Junk: i [remote] Junk: e [remote] Junk: d [remote] Junk: ^M [remote] Junk: [remote] Junk: [ [remote] Junk: 2 [remote] Junk: ] [remote] Junk: k [remote] Junk: d [remote] Junk: b [remote] Junk: > [remote] Junk: [remote] Junk: : [remote] Junk: m [remote] Junk: u [remote] Junk: l [remote] Junk: t [remote] Junk: i [remote] Junk: p [remote] Junk: r [remote] Junk: o [remote] Junk: c [remote] Junk: e [remote] Junk: s [remote] Junk: s [remote] Received Ack [remote] read_frame: Bad checksum, sentsum=0xec, csum=0x8, buf=qSupporteddiag: -22: Permission denied\r\n[2]kdb> :multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-events+;exec-events+;vContSupported+;QThreadEvents+;no-resumed+;memory-tagging+ [remote] getpkt: Timed out. [remote] getpkt: Timed out. Ignoring packet error, continuing... [remote] packet_ok: Packet qSupported (supported-packets) is supported [remote] Sending packet: $vCont?#49 [remote] Received Nak [remote] Sending packet: $vCont?#49 [remote] Received Ack [remote] Packet received: vCont? [remote] packet_ok: Packet vCont (verbose-resume) is NOT supported [remote] packet_ok: Packet vCont (verbose-resume) is NOT supported [remote] Sending packet: $vMustReplyEmpty#3a [remote] putpkt_binary: Packet instead of Ack, ignoring it [remote] Received Ack [remote] Packet received: vMustReplyEmpty [remote] start_remote_1: exit Remote replied unexpectedly to 'vMustReplyEmpty': vMustReplyEmpty +quit It seems the target is denying permission. I’ve been searching around but have not found anything similar. I tried opening the permissions on the /dev/ttyS1 on both VM’s to rwxrwxrwx and that doesn’t help. There are no SELinux warnings on the debugger VM. I don’t know if SELinux is causing a problem on the target VM. More details about the configuration: I’m running two Rocky 9.3 VM’s on Windows Hyper-V that I have connected over a named pipe using the Powershell Set-VMComport commands: Set-VMComport -VMName "Rocky-Debugger" -Number 2 -Path \\.\pipe\rocky-pipe-2 Set-VMComport -VMName "Rocky " -Number 2 -Path \\.\pipe\rocky-pipe-2 I downloaded the 6.8.5 kernel from the kernel.org website and compiled it on the “Rocky” vm using the following configuration: # # Generic Kernel Debugging Instruments # CONFIG_MAGIC_SYSRQ=y CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1 CONFIG_MAGIC_SYSRQ_SERIAL=y CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE="" CONFIG_DEBUG_FS=y CONFIG_DEBUG_FS_ALLOW_ALL=y # CONFIG_DEBUG_FS_DISALLOW_MOUNT is not set # CONFIG_DEBUG_FS_ALLOW_NONE is not set CONFIG_HAVE_ARCH_KGDB=y CONFIG_KGDB=y CONFIG_KGDB_HONOUR_BLOCKLIST=y CONFIG_KGDB_SERIAL_CONSOLE=y CONFIG_KGDB_TESTS=y # CONFIG_KGDB_TESTS_ON_BOOT is not set CONFIG_KGDB_LOW_LEVEL_TRAP=y CONFIG_KGDB_KDB=y CONFIG_KDB_DEFAULT_ENABLE=0x0 CONFIG_KDB_KEYBOARD=y CONFIG_KDB_CONTINUE_CATASTROPHIC=0 CONFIG_ARCH_HAS_EARLY_DEBUG=y CONFIG_ARCH_HAS_UBSAN_SANITIZE_ALL=y # CONFIG_UBSAN is not set CONFIG_HAVE_ARCH_KCSAN=y CONFIG_HAVE_KCSAN_COMPILER=y # CONFIG_KCSAN is not set # end of Generic Kernel Debugging Instruments I added the kernel args “console=tty0 console=ttyS0,115200 kgdboc=ttyS1,115200”. I start the VM with the new kernel and run the command “echo g > /proc/sysrq-trigger”. On the “Rocky-debugger” vm, I added my user to “dialout”. The permissions on /dev/ttyS1 is rw for the group. I set the following in .gdbinit, “set serial baud 115200”. Run “gdb vmlinux”, then “target remote /dev/ttyS1”. That’s when I get the “Permission denied”. I can connect to the console over serial using “sudo screen ttyS0” and that works just fine. So I don’t believe it’s a Windows Hyper-V permissions issue. I’m out of ideas. Any help is appreciated! Thanks, Bryan Carroll |
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