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authorHui Li <lihui@loongson.cn>2024-06-21 04:18:40 +0200
committerHuacai Chen <chenhuacai@loongson.cn>2024-06-21 04:18:40 +0200
commitc8e57ab0995c5b443d3c81c8a36b588776dcd0c3 (patch)
tree510c1640f58742bbb37aa89ec9b62b2ff039c852 /arch/loongarch/include/asm
parentLoongArch: Fix watchpoint setting error (diff)
downloadlinux-c8e57ab0995c5b443d3c81c8a36b588776dcd0c3.tar.xz
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LoongArch: Trigger user-space watchpoints correctly
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>
Diffstat (limited to 'arch/loongarch/include/asm')
-rw-r--r--arch/loongarch/include/asm/hw_breakpoint.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/loongarch/include/asm/hw_breakpoint.h b/arch/loongarch/include/asm/hw_breakpoint.h
index a8ce580f4fc6..d78330916bd1 100644
--- a/arch/loongarch/include/asm/hw_breakpoint.h
+++ b/arch/loongarch/include/asm/hw_breakpoint.h
@@ -75,6 +75,8 @@ do { \
#define CSR_MWPC_NUM 0x3f
#define CTRL_PLV_ENABLE 0x1e
+#define CTRL_PLV0_ENABLE 0x02
+#define CTRL_PLV3_ENABLE 0x10
#define MWPnCFG3_LoadEn 8
#define MWPnCFG3_StoreEn 9