[Qemu-discuss] QEMU-SYSTEM-ARM, GDB and SemiHosting

[Robert N]

I am doing some bare metal ARM Cortex-M3 development with qemu-system-arm and 
when I run qemu (withOUT gdb) against my axf(elf) file, everything works fine. 
I get my ""bkpt #0xAB" semi-hosting "SYS_WRITE0" strings printed to stdout as 
you would expect.

I can use gdb and debug the same axf file using qemu with the "-S -s" options, 
set breakpoints, next, cont, nexti, etc.. no problems there.

But, when using gdb I do not get any semi-hosting output at all. Neither in the 
qemu terminal (or when monitor is set to stdio), nor do I get the messages in 
gdb as I would expect to.

I do not see signaling being done to gdb when "set debug remote 1" is active at 
the time a Thumb bkpt service call is executed.

Is semi-hosting and gdb usage within QEMU mutually exclusive by design? a 
know/unknown bug? my configuration?

Thanks in advance for any help on this...

-R

qemu-system-arm --version
QEMU emulator version 1.7.50, Copyright (c) 2003-2008 Fabrice Bellard

qemu-system-arm -cpu cortex-m3 -nographic -semihosting -kernel 
bin/rtos_motor_controller.axf -s -S

arm-none-eabi-gdb --version
GNU gdb (GDB) 7.7.50.20140228-cvs

(gdb)next
Sending packet: $Z0,4c,2#ab...Ack
Packet received: OK
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
0b0200000400000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000000000000b00f02000f0100008800000073030000
Sending packet: $m88,4#3d...Ack
Packet received: 01900091
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
0b0200000400000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000000000000b00f02000f0100008a00000073030000
Sending packet: $m8a,4#66...Ack
Packet received: 0091ddf8
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
0b0200000400000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000000000000b00f02000f0100008c00000073030000
Sending packet: $m8c,4#68...Ack
Packet received: ddf800c0
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
0b0200000400000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000b00f02000f0100009000000073030000
Sending packet: $m90,4#36...Ack
Packet received: ddf804e0
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
0b0200000400000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000b00f02000b0200009400000073030000
Sending packet: $m94,4#3a...Ack
Packet received: 60467146
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
040000000400000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000b00f02000b0200009600000073030000
Sending packet: $m96,4#3c...Ack
Packet received: 7146abbe
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
040000000b02000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000b00f02000b0200009800000073030000
Sending packet: $m98,4#3e...Ack
Packet received: abbe0998
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: Fwrite,2,0000020b,00000018\n
Sending packet: $F-1,5#05...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
010000000b02000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000b00f02000b0200009c00000073030000
Sending packet: $m9c,4#69...Ack
Packet received: 0cb0bde8
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
010000000b02000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000e00f02000b0200009e00000073030000
Sending packet: $m9e,4#6b...Ack
Packet received: bde80088
Sending packet: $vCont;s:1;c#c1...Ack
Packet received: T05thread:01;
Sending packet: $g#67...Ack
Packet received: 
010000000b02000004000000f2010000000000000000000000000000f80f02000000000000000000000000000000000004000000e80f02000b0200000e01000073030000
Sending packet: $m10e,4#93...Ack
Packet received: 019004b0
Sending packet: $m20ffc,4#5e...Ack
Packet received: 00000000
Sending packet: $m20ffc,4#5e...Ack
Packet received: 00000000
Sending packet: $m0,4#fd...Ack
Packet received: 00100200
Sending packet: $m20ffc,4#5e...Ack
Packet received: 00000000
Sending packet: $m0,4#fd...Ack
Packet received: 00100200
Sending packet: $z0,4c,2#cb...Ack
Packet received: OK
(gdb)