[PATCH] arm64: fix single step issue in kgdb

[Wei Li]

From: Wei Li <liwei1412 at 163.com>

In kdb, as the frontend for kgdb, cmd "ss" does not work well. It can only take effects once and the single step exception is reported as oops after a breakpoint triggered in kdb. Then the cmd "go" does not work well either due to this. Refer to the DDI0487C_a_armv8_arm.pdf (D2.12), i set the SPSR.SS=1 every time. It has been verified in qemu.

Signed-off-by: Wei Li <liwei1412 at 163.com>
---
 include/asm/debug-monitors.h |    3 +++
 kernel/debug-monitors.c      |    4 ++--
 kernel/kgdb.c                |    3 ++-
 3 files changed, 7 insertions(+), 3 deletions(-)
 
diff -uprN linux-4.16.2_org/arch/arm64/include/asm/debug-monitors.h linux-4.16.2_mod/arch/arm64/include/asm/debug-monitors.h
--- linux-4.16.2_org/arch/arm64/include/asm/debug-monitors.h    2018-04-12 18:30:01.000000000 +0800
+++ linux-4.16.2_mod/arch/arm64/include/asm/debug-monitors.h    2018-04-19 00:19:10.134999268 +0800
@@ -135,6 +135,9 @@ static inline int reinstall_suspended_bp
 
 int aarch32_break_handler(struct pt_regs *regs);
 
+void set_regs_spsr_ss(struct pt_regs *regs);
+void clear_regs_spsr_ss(struct pt_regs *regs);
+
 #endif    /* __ASSEMBLY */
 #endif    /* __KERNEL__ */
 #endif    /* __ASM_DEBUG_MONITORS_H */
diff -uprN linux-4.16.2_org/arch/arm64/kernel/debug-monitors.c linux-4.16.2_mod/arch/arm64/kernel/debug-monitors.c
--- linux-4.16.2_org/arch/arm64/kernel/debug-monitors.c    2018-04-12 18:30:01.000000000 +0800
+++ linux-4.16.2_mod/arch/arm64/kernel/debug-monitors.c    2018-04-19 00:19:19.435189356 +0800
@@ -150,13 +150,13 @@ postcore_initcall(debug_monitors_init);
 /*
  * Single step API and exception handling.
  */
-static void set_regs_spsr_ss(struct pt_regs *regs)
+void set_regs_spsr_ss(struct pt_regs *regs)
 {
     regs->pstate |= DBG_SPSR_SS;
 }
 NOKPROBE_SYMBOL(set_regs_spsr_ss);
 
-static void clear_regs_spsr_ss(struct pt_regs *regs)
+void clear_regs_spsr_ss(struct pt_regs *regs)
 {
     regs->pstate &= ~DBG_SPSR_SS;
 }
diff -uprN linux-4.16.2_org/arch/arm64/kernel/kgdb.c linux-4.16.2_mod/arch/arm64/kernel/kgdb.c
--- linux-4.16.2_org/arch/arm64/kernel/kgdb.c    2018-04-12 18:30:01.000000000 +0800
+++ linux-4.16.2_mod/arch/arm64/kernel/kgdb.c    2018-04-19 00:19:40.892911795 +0800
@@ -221,6 +221,7 @@ int kgdb_arch_handle_exception(int excep
         /*
          * Enable single step handling
          */
+        set_regs_spsr_ss(linux_regs);
         if (!kernel_active_single_step())
             kernel_enable_single_step(linux_regs);
         err = 0;
@@ -252,7 +253,7 @@ static int kgdb_step_brk_fn(struct pt_re
     if (!kgdb_single_step)
         return DBG_HOOK_ERROR;
 
-    kgdb_handle_exception(1, SIGTRAP, 0, regs);
+    kgdb_handle_exception(0, SIGTRAP, 0, regs);
     return 0;
 }
 NOKPROBE_SYMBOL(kgdb_step_brk_fn);