Tiezhu Yang 7c86ff9925 MIPS: Add basic support for ptrace single step ... 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> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>		2021-02-13 09:49:19 +01:00
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asm	MIPS: Add basic support for ptrace single step	2021-02-13 09:49:19 +01:00
uapi/asm	MIPS: kernel: Support extracting off-line stack traces from user-space with perf	2021-02-04 21:55:45 +01:00