cannot set GDB watchpoints on QEMU x86 with icount enabled

[andrewboie]

Describe the bug

If I try to watch a memory address:

(gdb) p &z_idle_threads[0].arch.rsi
$1 = (uint64_t *) 0x116f20 <z_idle_threads+352>
(gdb) x/fx 0x116f20
0x116f20 <z_idle_threads+352>:  0x00000000
(gdb) watch *0x116f20
Hardware watchpoint 2: *0x116f20
(gdb) c
Continuing.

The emulator explodes:

qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:ECX.x2apic [bit 21]
SeaBIOS (version rel-1.12.1-0-ga5cab58-dirty-20200625_115407-9426dddc0a1f-zephyr
)
Booting from ROM..qemu: fatal: Raised interrupt while not in I/O function
EAX=00000000 EBX=00009500 ECX=000000df EDX=00000511
ESI=00000000 EDI=00116f20 EBP=00000000 ESP=00006f08
EIP=00008031 EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00cf9a00 DPL=0 CS32 [-R-]
SS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     0000c070 0000004f
IDT=     00009000 00000fff
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=004a8000 CCD=00950000 CCO=CLR
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000 XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000 XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000 XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 XMM07=00000000000000000000000000000000

This only happens with icount enabled. I have seen this on x86 32-bit, and on x86_64 with CONFIG_MP_NUM_CPUS=1 (which enables icount since we only have one CPU)

To Reproduce
Steps to reproduce the behavior:

1. Build some test application and set a watch to some symbol or memory address in RAM in GDB
2. Continue execution

Expected behavior
GDB watches the memory as expected.

Impact
Annoyance to moderate. Disabling icount adds variance to test results and things may not be reproducible, and x86 is VERY difficult to get a real debugger attached for HW testing

[galak]

Can you try w/qemu 5.1:

builds.zephyrproject.org/zephyrproject-rtos/sdk-ng/272/zephyr-sdk-0.11.4-pr-272-x86_64-linux-setup.run

If still an issue, this should be filed w/upstream qemu.

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[stsquad]

The next QEMU release (6.2) has a fix for the watchpoint with icount bug.