Messages in this thread Patch in this message | | | From | Wei Li <> | Subject | [PATCH 4/4] arm64: kgdb: Set PSTATE.SS to 1 to reenable single-step | Date | Sun, 10 May 2020 05:41:59 +0800 |
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After fixing wrongly single-stepping into the irq handler, when we execute single-step in kdb/kgdb, we can see only the first step can work.
Refer to the ARM Architecture Reference Manual (ARM DDI 0487E.a) D2.12, i think PSTATE.SS=1 should be set each step for transferring the PE to the 'Active-not-pending' state. The problem here is PSTATE.SS=1 is not set since the second single-step.
After the first single-step, the PE transferes to the 'Inactive' state, with PSTATE.SS=0 and MDSCR.SS=1, thus PSTATE.SS won't be set to 1 due to kernel_active_single_step()=true. Then the PE transferes to the 'Active-pending' state when ERET and returns to the debugger by step exception.
Before this patch: * kdb: Entering kdb (current=0xffff8000119d2dc0, pid 0) on processor 0 due to Keyboard Entry [0]kdb> bp printk Instruction(i) BP #0 at 0xffff80001014874c (printk) is enabled addr at ffff80001014874c, hardtype=0 installed=0
[0]kdb> g
/ # echo h > /proc/sysrq-trigger
Entering kdb (current=0xffff0000fa6948c0, pid 265) on processor 3 due to Breakpoint @ 0xffff80001014874c [3]kdb> ss
Entering kdb (current=0xffff0000fa6948c0, pid 265) on processor 3 due to SS trap @ 0xffff800010148750 [3]kdb> ss
Entering kdb (current=0xffff0000fa6948c0, pid 265) on processor 3 due to SS trap @ 0xffff800010148750 [3]kdb> ss
Entering kdb (current=0xffff0000fa6948c0, pid 265) on processor 3 due to SS trap @ 0xffff800010148750 [3]kdb>
* kgdb: (gdb) target remote 127.1:23002 Remote debugging using 127.1:23002 arch_kgdb_breakpoint () at /home/liwei/main_code/linux/arch/arm64/include/asm/kgdb.h:21 21 asm ("brk %0" : : "I" (KGDB_COMPILED_DBG_BRK_IMM)); (gdb) b printk Breakpoint 1 at 0xffff80001014874c: file /home/liwei/main_code/linux/kernel/printk/printk.c, line 2076. (gdb) c Continuing. [New Thread 277] [Switching to Thread 276]
Thread 171 hit Breakpoint 1, printk (fmt=0xffff8000112fc130 "\001\066sysrq: HELP : ") at /home/liwei/main_code/linux/kernel/printk/printk.c:2076 2076 { (gdb) stepi 0xffff800010148750 2076 { (gdb) stepi 0xffff800010148750 2076 { (gdb) stepi 0xffff800010148750 2076 { (gdb)
After this patch: * kdb: Entering kdb (current=0xffff8000119d2dc0, pid 0) on processor 0 due to Keyboard Entry [0]kdb> bp printk Instruction(i) BP #0 at 0xffff80001014874c (printk) is enabled addr at ffff80001014874c, hardtype=0 installed=0
[0]kdb> g
/ # echo h > /proc/sysrq-trigger
Entering kdb (current=0xffff0000fa800040, pid 264) on processor 2 due to Breakpoint @ 0xffff80001014874c [2]kdb> ss
Entering kdb (current=0xffff0000fa800040, pid 264) on processor 2 due to SS trap @ 0xffff800010148750 [2]kdb> ss
Entering kdb (current=0xffff0000fa800040, pid 264) on processor 2 due to SS trap @ 0xffff800010148754 [2]kdb> ss
Entering kdb (current=0xffff0000fa800040, pid 264) on processor 2 due to SS trap @ 0xffff800010148758 [2]kdb>
* kgdb: (gdb) target remote 127.1:23002 Remote debugging using 127.1:23002 arch_kgdb_breakpoint () at /home/liwei/main_code/linux/arch/arm64/include/asm/kgdb.h:21 21 asm ("brk %0" : : "I" (KGDB_COMPILED_DBG_BRK_IMM)); (gdb) b printk Breakpoint 1 at 0xffff80001014874c: file /home/liwei/main_code/linux/kernel/printk/printk.c, line 2076. (gdb) c Continuing. [New Thread 281] [New Thread 280] [Switching to Thread 281]
Thread 174 hit Breakpoint 1, printk (fmt=0xffff8000112fc138 "\001\066sysrq: HELP : ") at /home/liwei/main_code/linux/kernel/printk/printk.c:2076 2076 { (gdb) stepi 0xffff800010148750 2076 { (gdb) stepi 2080 va_start(args, fmt); (gdb) stepi 0xffff800010148758 2080 va_start(args, fmt); (gdb)
Fixes: 44679a4f142b ("arm64: KGDB: Add step debugging support") Signed-off-by: Wei Li <liwei391@huawei.com> --- arch/arm64/include/asm/debug-monitors.h | 2 ++ arch/arm64/kernel/debug-monitors.c | 2 +- arch/arm64/kernel/kgdb.c | 3 ++- 3 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h index b62469f3475b..a48b507c89ee 100644 --- a/arch/arm64/include/asm/debug-monitors.h +++ b/arch/arm64/include/asm/debug-monitors.h @@ -78,6 +78,8 @@ struct step_hook { int (*fn)(struct pt_regs *regs, unsigned int esr); }; +void set_regs_spsr_ss(struct pt_regs *regs); + void register_user_step_hook(struct step_hook *hook); void unregister_user_step_hook(struct step_hook *hook); diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index 25ce6b5a52d2..7a58233677de 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -141,7 +141,7 @@ 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; } diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c index 3910ac06c261..093ad9d2e5e6 100644 --- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -230,7 +230,8 @@ int kgdb_arch_handle_exception(int exception_vector, int signo, kernel_prepare_single_step(&per_cpu(kgdb_ss_flags, raw_smp_processor_id()), linux_regs); kernel_enable_single_step(linux_regs); - } + } else + set_regs_spsr_ss(linux_regs); err = 0; break; -- 2.17.1
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