Revert "csky: Fixup CONFIG_DEBUG_RSEQ"

This reverts commit f36e0aab6f.

The csky rseq support has been merged without ever notifying the rseq
maintainers, and without any of the required asssembler glue in the rseq
selftests, which means it is entirely untested.

It is also derived from a non-upstream riscv patch which has known bugs.

The assembly part of this revert should be carefully reviewed by the
architecture maintainer because it touches code which has changed since
the merge of the reverted patch.

The rseq selftests assembly glue should be introduced at the same time
as the architecture rseq support. Without the presence of any test, I
recommend reverting rseq support from csky for now.

Link: https://lore.kernel.org/lkml/1257037909.25426.1626705790861.JavaMail.zimbra@efficios.com/
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-csky@vger.kernel.org

arch/csky/kernel/entry.S

@@ -50,11 +50,15 @@ ENTRY(csky_systemcall)
 	SAVE_ALL TRAP0_SIZE
 	zero_fp
 	context_tracking
+#ifdef CONFIG_RSEQ_DEBUG
+	mov     a0, sp
+	jbsr    rseq_syscall
+#endif
 	psrset  ee, ie
 
 	lrw     r9, __NR_syscalls
 	cmphs   syscallid, r9		/* Check nr of syscall */
-	bt      1f
+	bt      ret_from_exception
 
 	lrw     r9, sys_call_table
 	ixw     r9, syscallid
@@ -80,11 +84,6 @@ ENTRY(csky_systemcall)
 	jsr     syscallid
 #endif
 	stw     a0, (sp, LSAVE_A0)      /* Save return value */
-1:
-#ifdef CONFIG_DEBUG_RSEQ
-	mov	a0, sp
-	jbsr	rseq_syscall
-#endif
 	jmpi    ret_from_exception
 
 csky_syscall_trace:
@@ -113,10 +112,6 @@ csky_syscall_trace:
 	stw	a0, (sp, LSAVE_A0)	/* Save return value */
 
 1:
-#ifdef CONFIG_DEBUG_RSEQ
-	mov	a0, sp
-	jbsr	rseq_syscall
-#endif
 	mov     a0, sp                  /* right now, sp --> pt_regs */
 	jbsr    syscall_trace_exit
 	br	ret_from_exception