ptrace: move user_enable_single_step & co prototypes to linux/ptrace.h

While in theory user_enable_single_step/user_disable_single_step/
user_enable_blockstep could also be provided as an inline or macro there's
no good reason to do so, and having the prototype in one places keeps code
size and confusion down.

Roland said:

The original thought there was that user_enable_single_step() et al
might well be only an instruction or three on a sane machine (as if we
have any of those!), and since there is only one call site inlining
would be beneficial. But I agree that there is no strong reason to care
about inlining it.

As to the arch changes, there is only one thought I'd add to the
record. It was always my thinking that for an arch where
PTRACE_SINGLESTEP does text-modifying breakpoint insertion,
user_enable_single_step() should not be provided. That is,
arch_has_single_step()=>true means that there is an arch facility with
"pure" semantics that does not have any unexpected side effects.
Inserting a breakpoint might do very unexpected strange things in
multi-threaded situations. Aside from that, it is a peculiar side
effect that user_{enable,disable}_single_step() should cause COW
de-sharing of text pages and so forth. For PTRACE_SINGLESTEP, all these
peculiarities are the status quo ante for that arch, so having
arch_ptrace() itself do those is one thing. But for building other
things in the future, it is nicer to have a uniform "pure" semantics
that arch-independent code can expect.

OTOH, all such arch issues are really up to the arch maintainer. As
of today, there is nothing but ptrace using user_enable_single_step() et
al so it's a distinction without a practical difference. If/when there
are other facilities that use user_enable_single_step() and might care,
the affected arch's can revisit the question when someone cares about
the quality of the arch support for said new facility.

Signed-off-by: Christoph Hellwig <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Roland McGrath <[e-mail]>
Acked-by: David Howells <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/frv/include/asm/ptrace.h

···
 #define task_pt_regs(task) ((task)->thread.frame0)
 
 #define arch_has_single_step()	(1)
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
 
 #endif /* !__ASSEMBLY__ */
 #endif /* __KERNEL__ */

arch/ia64/include/asm/ptrace.h

···
 	ptrace_attach_sync_user_rbs(child)
 
   #define arch_has_single_step()  (1)
-  extern void user_enable_single_step(struct task_struct *);
-  extern void user_disable_single_step(struct task_struct *);
-
   #define arch_has_block_step()   (1)
-  extern void user_enable_block_step(struct task_struct *);
 
 #endif /* !__KERNEL__ */
 

arch/m68k/include/asm/ptrace.h

···
 #define profile_pc(regs) instruction_pointer(regs)
 extern void show_regs(struct pt_regs *);
 
-/*
- * These are defined as per linux/ptrace.h.
- */
-struct task_struct;
-
 #define arch_has_single_step()	(1)
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
 
 #ifdef CONFIG_MMU
 #define arch_has_block_step()	(1)
-extern void user_enable_block_step(struct task_struct *);
 #endif
 
 #endif /* __KERNEL__ */

arch/mn10300/include/asm/ptrace.h

···
 extern void show_regs(struct pt_regs *);
 
 #define arch_has_single_step()	(1)
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
 
 #endif  /*  !__ASSEMBLY  */
 

arch/parisc/include/asm/ptrace.h

···
 
 #define task_regs(task) ((struct pt_regs *) ((char *)(task) + TASK_REGS))
 
-struct task_struct;
 #define arch_has_single_step()	1
-void user_disable_single_step(struct task_struct *task);
-void user_enable_single_step(struct task_struct *task);
-
 #define arch_has_block_step()	1
-void user_enable_block_step(struct task_struct *task);
 
 /* XXX should we use iaoq[1] or iaoq[0] ? */
 #define user_mode(regs)			(((regs)->iaoq[0] & 3) ? 1 : 0)

arch/powerpc/include/asm/ptrace.h

···
 } while (0)
 #endif /* __powerpc64__ */
 
-/*
- * These are defined as per linux/ptrace.h, which see.
- */
 #define arch_has_single_step()	(1)
 #define arch_has_block_step()	(!cpu_has_feature(CPU_FTR_601))
-extern void user_enable_single_step(struct task_struct *);
-extern void user_enable_block_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
-
 #define ARCH_HAS_USER_SINGLE_STEP_INFO
 
 #endif /* __ASSEMBLY__ */

arch/s390/include/asm/ptrace.h

···
  * These are defined as per linux/ptrace.h, which see.
  */
 #define arch_has_single_step()	(1)
-struct task_struct;
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
 extern void show_regs(struct pt_regs * regs);
 
 #define user_mode(regs) (((regs)->psw.mask & PSW_MASK_PSTATE) != 0)

arch/score/include/asm/ptrace.h

···
 			 unsigned short *);
 
 #define arch_has_single_step()	(1)
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
+
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_SCORE_PTRACE_H */

arch/sh/include/asm/ptrace.h

···
 struct task_struct;
 
 #define arch_has_single_step()	(1)
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
 
 struct perf_event;
 struct perf_sample_data;

arch/x86/include/asm/ptrace.h

···
 		return 0;
 }
 
-/*
- * These are defined as per linux/ptrace.h, which see.
- */
 #define arch_has_single_step()	(1)
-extern void user_enable_single_step(struct task_struct *);
-extern void user_disable_single_step(struct task_struct *);
-
-extern void user_enable_block_step(struct task_struct *);
 #ifdef CONFIG_X86_DEBUGCTLMSR
 #define arch_has_block_step()	(1)
 #else

include/linux/ptrace.h

···
 static inline void user_disable_single_step(struct task_struct *task)
 {
 }
+#else
+extern void user_enable_single_step(struct task_struct *);
+extern void user_disable_single_step(struct task_struct *);
 #endif	/* arch_has_single_step */
 
 #ifndef arch_has_block_step
···
 {
 	BUG();			/* This can never be called.  */
 }
+#else
+extern void user_enable_block_step(struct task_struct *);
 #endif	/* arch_has_block_step */
 
 #ifdef ARCH_HAS_USER_SINGLE_STEP_INFO