Subject: Re: [PATCH V3 3/3] powerpc, ptrace: Enable support for miscellaneous registers

From: Anshuman Khandual <[email-masked]>
Date: Wed, 08 Oct 2014 21:50:20 +0530

On 08/28/2014 03:05 AM, Sukadev Bhattiprolu wrote:
> 
> Anshuman Khandual [[email-masked]] wrote:
> | This patch enables get and set of miscellaneous registers through ptrace
> | PTRACE_GETREGSET/PTRACE_SETREGSET interface by implementing new powerpc
> | specific register set REGSET_MISC support corresponding to the new ELF
> | core note NT_PPC_MISC added previously in this regard.
> | 
> | Signed-off-by: Anshuman Khandual <[email-masked]>
> | ---
> |  arch/powerpc/kernel/ptrace.c | 81 ++++++++++++++++++++++++++++++++++++++++++++
> |  1 file changed, 81 insertions(+)
> | 
> | diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> | index 17642ef..63b883a 100644
> | --- a/arch/powerpc/kernel/ptrace.c
> | +++ b/arch/powerpc/kernel/ptrace.c
> | @@ -1149,6 +1149,76 @@ static int tm_cvmx_set(struct task_struct *target, const struct user_regset *reg
> |  #endif	/* CONFIG_PPC_TRANSACTIONAL_MEM */
> |  
> |  /*
> | + * Miscellaneous Registers
> | + *
> | + * struct {
> | + * 	unsigned long dscr;
> | + *	unsigned long ppr;
> | + * 	unsigned long tar;
> | + * };
> | + */
> | +static int misc_get(struct task_struct *target, const struct user_regset *regset,
> | +		   unsigned int pos, unsigned int count,
> | +		   void *kbuf, void __user *ubuf)
> | +{
> | +	int ret;
> | +
> | +	/* DSCR register */
> | +	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> | +					&target->thread.dscr, 0,
> | +					sizeof(unsigned long));
> | +
> | +	BUILD_BUG_ON(offsetof(struct thread_struct, dscr) + sizeof(unsigned long) +
> | +				sizeof(unsigned long) != offsetof(struct thread_struct, ppr));
> 
> 
> I see these in  arch/powerpc/include/asm/processor.h
> 
> #ifdef CONFIG_PPC64
>         unsigned long   dscr;
>         int             dscr_inherit;
>         unsigned long   ppr;    /* used to save/restore SMT priority */
> #endif
> 
> where there is an 'int' between ppr and dscr. So, should one of
> the above sizeof(unsigned long) be changed to sizeof(int) ?

Right, I understand that but strangely I get this compile time error
when it is changed to sizeof(int).

 error: call to ‘__compiletime_assert_1350’ declared with attribute error:
  BUILD_BUG_ON failed: TSO(dscr) + sizeof(unsigned long) + sizeof(int) != TSO(ppr)
  BUILD_BUG_ON(TSO(dscr) + sizeof(unsigned long) + sizeof(int) != TSO(ppr));

may be I am missing something here.

> 
> Also, since we use offsetof(struct thread_struct, field) heavily, a
> macro local to the file, may simplify the code.

Right, will do that.

> #define	TSO(f)	(offsetof(struct thread_struct, f))
> 
> | +
> | +	/* PPR register */
> | +	if (!ret)
> | +		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> | +					  &target->thread.ppr, sizeof(unsigned long),
> | +					  2 * sizeof(unsigned long));
> | +
> | +	BUILD_BUG_ON(offsetof(struct thread_struct, ppr) + sizeof(unsigned long)
> | +						!= offsetof(struct thread_struct, tar));
> | +	/* TAR register */
> | +	if (!ret)
> | +		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> | +					  &target->thread.tar, 2 * sizeof(unsigned long),
> | +					  3 * sizeof(unsigned long));
> | +	return ret;
> | +}
> | +
> | +static int misc_set(struct task_struct *target, const struct user_regset *regset,
> | +		   unsigned int pos, unsigned int count,
> | +		   const void *kbuf, const void __user *ubuf)
> | +{
> | +	int ret;
> | +
> | +	/* DSCR register */
> | +	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
> | +					&target->thread.dscr, 0,
> | +					sizeof(unsigned long));
> | +
> | +	BUILD_BUG_ON(offsetof(struct thread_struct, dscr) + sizeof(unsigned long) +
> | +			sizeof(unsigned long) != offsetof(struct thread_struct, ppr));
> | +
> | +	/* PPR register */
> | +	if (!ret)
> | +		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
> | +						&target->thread.ppr, sizeof(unsigned long),
> | +						2 * sizeof(unsigned long));
> | +
> | +	BUILD_BUG_ON(offsetof(struct thread_struct, ppr) + sizeof(unsigned long)
> | +						!= offsetof(struct thread_struct, tar));
> | +
> | +	/* TAR register */
> | +	if (!ret)
> | +		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
> | +						&target->thread.tar, 2 * sizeof(unsigned long),
> | +						3 * sizeof(unsigned long));
> | +	return ret;
> | +}
> | +
> | +/*
> |   * These are our native regset flavors.
> |   */
> |  enum powerpc_regset {
> | @@ -1169,6 +1239,7 @@ enum powerpc_regset {
> |  	REGSET_TM_CFPR,		/* TM checkpointed FPR */
> |  	REGSET_TM_CVMX,		/* TM checkpointed VMX */
> |  #endif
> | +	REGSET_MISC		/* Miscellaneous */
> |  };
> |  
> |  static const struct user_regset native_regsets[] = {
> | @@ -1225,6 +1296,11 @@ static const struct user_regset native_regsets[] = {
> |  		.active = tm_cvmx_active, .get = tm_cvmx_get, .set = tm_cvmx_set
> |  	},
> |  #endif
> | +	[REGSET_MISC] = {
> | +		.core_note_type = NT_PPC_MISC, .n = 3,
> | +		.size = sizeof(u64), .align = sizeof(u64),
> | +		.get = misc_get, .set = misc_set
> | +	},
> |  };
> |  
> |  static const struct user_regset_view user_ppc_native_view = {
> | @@ -1566,6 +1642,11 @@ static const struct user_regset compat_regsets[] = {
> |  		.active = tm_cvmx_active, .get = tm_cvmx_get, .set = tm_cvmx_set
> |  	},
> |  #endif
> | +	[REGSET_MISC] = {
> | +		.core_note_type = NT_PPC_MISC, .n = 3,
> | +		.size = sizeof(u64), .align = sizeof(u64),
> | +		.get = misc_get, .set = misc_set
> | +	},
> 
> Since the .n = 3 is used more than once, how about a macro for the
> number of misc registers ?

Will add it as well. Thanks !