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SubjectRe: [PATCH v2 RESEND] MIPS: Add basic support for ptrace single step
On Sat, Feb 13, 2021 at 02:20:46AM +0800, Tiezhu Yang wrote:
> From: Tiezhu Yang <yangtiezhu@loongson.cn>
>
> 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@loongson.cn>
> Signed-off-by: Xingxing Su <suxingxing@loongson.cn>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
>
> 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 ]

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