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In the current code, gdb can set the watchpoint successfully through
ptrace interface, but watchpoint will not be triggered.
When debugging the following code using gdb.
lihui@bogon:~$ cat test.c
#include <stdio.h>
int a = 0;
int main()
{
a = 1;
printf("a = %d\n", a);
return 0;
}
lihui@bogon:~$ gcc -g test.c -o test
lihui@bogon:~$ gdb test
...
(gdb) watch a
...
(gdb) r
...
a = 1
[Inferior 1 (process 4650) exited normally]
No watchpoints were triggered, the root causes are:
1. Kernel uses perf_event and hw_breakpoint framework to control
watchpoint, but the perf_event corresponding to watchpoint is
not enabled. So it needs to be enabled according to MWPnCFG3
or FWPnCFG3 PLV bit field in ptrace_hbp_set_ctrl(), and privilege
is set according to the monitored addr in hw_breakpoint_control().
Furthermore, add a judgment in ptrace_hbp_set_addr() to ensure
kernel-space addr cannot be monitored in user mode.
2. The global enable control for all watchpoints is the WE bit of
CSR.CRMD, and hardware sets the value to 0 when an exception is
triggered. When the ERTN instruction is executed to return, the
hardware restores the value of the PWE field of CSR.PRMD here.
So, before a thread containing watchpoints be scheduled, the PWE
field of CSR.PRMD needs to be set to 1. Add this modification in
hw_breakpoint_control().
All changes according to the LoongArch Reference Manual:
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#control-and-status-registers-related-to-watchpoints
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#basic-control-and-status-registers
With this patch:
lihui@bogon:~$ gdb test
...
(gdb) watch a
Hardware watchpoint 1: a
(gdb) r
...
Hardware watchpoint 1: a
Old value = 0
New value = 1
main () at test.c:6
6 printf("a = %d\n", a);
(gdb) c
Continuing.
a = 1
[Inferior 1 (process 775) exited normally]
Cc: stable@vger.kernel.org
Signed-off-by: Hui Li <lihui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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In the current code, when debugging the following code using gdb,
"invalid argument ..." message will be displayed.
lihui@bogon:~$ cat test.c
#include <stdio.h>
int a = 0;
int main()
{
a = 1;
return 0;
}
lihui@bogon:~$ gcc -g test.c -o test
lihui@bogon:~$ gdb test
...
(gdb) watch a
Hardware watchpoint 1: a
(gdb) r
...
Invalid argument setting hardware debug registers
There are mainly two types of issues.
1. Some incorrect judgment condition existed in user_watch_state
argument parsing, causing -EINVAL to be returned.
When setting up a watchpoint, gdb uses the ptrace interface,
ptrace(PTRACE_SETREGSET, tid, NT_LOONGARCH_HW_WATCH, (void *) &iov)).
Register values in user_watch_state as follows:
addr[0] = 0x0, mask[0] = 0x0, ctrl[0] = 0x0
addr[1] = 0x0, mask[1] = 0x0, ctrl[1] = 0x0
addr[2] = 0x0, mask[2] = 0x0, ctrl[2] = 0x0
addr[3] = 0x0, mask[3] = 0x0, ctrl[3] = 0x0
addr[4] = 0x0, mask[4] = 0x0, ctrl[4] = 0x0
addr[5] = 0x0, mask[5] = 0x0, ctrl[5] = 0x0
addr[6] = 0x0, mask[6] = 0x0, ctrl[6] = 0x0
addr[7] = 0x12000803c, mask[7] = 0x0, ctrl[7] = 0x610
In arch_bp_generic_fields(), return -EINVAL when ctrl.len is
LOONGARCH_BREAKPOINT_LEN_8(0b00). So delete the incorrect judgment here.
In ptrace_hbp_fill_attr_ctrl(), when note_type is NT_LOONGARCH_HW_WATCH
and ctrl[0] == 0x0, if ((type & HW_BREAKPOINT_RW) != type) will return
-EINVAL. Here ctrl.type should be set based on note_type, and unnecessary
judgments can be removed.
2. The watchpoint argument was not set correctly due to unnecessary
offset and alignment_mask.
Modify ptrace_hbp_fill_attr_ctrl() and hw_breakpoint_arch_parse(), which
ensure the watchpont argument is set correctly.
All changes according to the LoongArch Reference Manual:
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#control-and-status-registers-related-to-watchpoints
Cc: stable@vger.kernel.org
Signed-off-by: Hui Li <lihui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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