On Sat, Feb 13, 2021 at 02:20:46AM +0800, Tiezhu Yang wrote: > From: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> > > In the current code, arch_has_single_step() is not defined on MIPS, > that means MIPS does not support instruction single-step for user mode. > > Delve is a debugger for the Go programming language, the ptrace syscall > PtraceSingleStep() failed [1] on MIPS and then the single step function > can not work well, we can see that PtraceSingleStep() definition returns > ptrace(PTRACE_SINGLESTEP) [2]. > > So it is necessary to support ptrace single step on MIPS. > > At the beginning, we try to use the Debug Single Step exception on the > Loongson 3A4000 platform, but it has no effect when set CP0_DEBUG SSt > bit, this is because CP0_DEBUG NoSSt bit is 1 which indicates no > single-step feature available [3], so this way which is dependent on the > hardware is almost impossible. > > With further research, we find out there exists a common way used with > break instruction in arch/alpha/kernel/ptrace.c, it is workable. > > For the above analysis, define arch_has_single_step(), add the common > function user_enable_single_step() and user_disable_single_step(), set > flag TIF_SINGLESTEP for child process, use break instruction to set > breakpoint. > > We can use the following testcase to test it: > tools/testing/selftests/breakpoints/step_after_suspend_test.c > > $ make -C tools/testing/selftests TARGETS=breakpoints > $ cd tools/testing/selftests/breakpoints > > Without this patch: > > $ ./step_after_suspend_test -n > TAP version 13 > 1..4 > # ptrace(PTRACE_SINGLESTEP) not supported on this architecture: Input/output error > ok 1 # SKIP CPU 0 > # ptrace(PTRACE_SINGLESTEP) not supported on this architecture: Input/output error > ok 2 # SKIP CPU 1 > # ptrace(PTRACE_SINGLESTEP) not supported on this architecture: Input/output error > ok 3 # SKIP CPU 2 > # ptrace(PTRACE_SINGLESTEP) not supported on this architecture: Input/output error > ok 4 # SKIP CPU 3 > # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:4 error:0 > > With this patch: > > $ ./step_after_suspend_test -n > TAP version 13 > 1..4 > ok 1 CPU 0 > ok 2 CPU 1 > ok 3 CPU 2 > ok 4 CPU 3 > # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:0 error:0 > > [1] https://github.com/go-delve/delve/blob/master/pkg/proc/native/threads_linux.go#L50 > [2] https://github.com/go-delve/delve/blob/master/vendor/golang.org/x/sys/unix/syscall_linux.go#L1573 > [3] http://www.t-es-t.hu/download/mips/md00047f.pdf > > Reported-by: Guoqi Chen <chenguoqi@xxxxxxxxxxx> > Signed-off-by: Xingxing Su <suxingxing@xxxxxxxxxxx> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> > Reported-by: kernel test robot <lkp@xxxxxxxxx> > --- > > RESEND due to send to mail list failed, sorry for that. > > v2: make union mips_instruction mips_insn = { 0 }; > to fix uninitialized build warning used with clang > reported by kernel test robot. > > arch/mips/include/asm/ptrace.h | 2 + > arch/mips/include/asm/thread_info.h | 5 ++ > arch/mips/kernel/ptrace.c | 108 ++++++++++++++++++++++++++++++++++++ > arch/mips/kernel/signal.c | 2 +- > 4 files changed, 116 insertions(+), 1 deletion(-) applied to mips-next. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]
