Patchwork powerpc: added DSCR support to ptrace

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Submitter Alexey Kardashevskiy
Date Jan. 11, 2013, 6:29 a.m.
Message ID <1357885749-14042-1-git-send-email-aik@ozlabs.ru>
Download mbox | patch
Permalink /patch/211211/
State Accepted
Commit 1715a826a5b72d4fb882504d0babcea9aec8a0db
Headers show

Comments

Alexey Kardashevskiy - Jan. 11, 2013, 6:29 a.m.
The DSCR (aka Data Stream Control Register) is supported on some
server PowerPC chips and allow some control over the prefetch
of data streams.

The kernel already supports DSCR value per thread but there is also
a need in a ability to change it from an external process for
the specific pid.

The patch adds new register index PT_DSCR (index=44) which can be
set/get by:
  ptrace(PTRACE_POKEUSER, traced_process, PT_DSCR << 3, dscr);
  dscr = ptrace(PTRACE_PEEKUSER, traced_process, PT_DSCR << 3, NULL);

The patch does not increase PT_REGS_COUNT as the pt_regs struct has not
been changed.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 arch/powerpc/include/uapi/asm/ptrace.h |    1 +
 arch/powerpc/kernel/ptrace.c           |   29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)
Benjamin Herrenschmidt - Jan. 15, 2013, 6:17 p.m.
On Fri, 2013-01-11 at 17:29 +1100, Alexey Kardashevskiy wrote:
> +static unsigned long get_user_dscr(struct task_struct *task)
> +{
> +       return -EIO;
> +}
> +

Does it make sense to return an error here ? ptrace_get_reg() doesn't
seem to have provisions for returning errors, it just return register
values, there's no way to differenciate an error code from a register
value as far as I can tell...

I'll apply your patch anyway because this is an existing problem with
that function (it already returns -EIO in other circumstances), but I
would like if you could submit a followup patch that changes it to
return the register by value and return a real error code, which can be
then handled properly in the two call sites (ptrace.c and ptrace32.c).

Cheers,
Ben.

Patch

diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
index ee67a2b..5a4863c 100644
--- a/arch/powerpc/include/uapi/asm/ptrace.h
+++ b/arch/powerpc/include/uapi/asm/ptrace.h
@@ -108,6 +108,7 @@  struct pt_regs {
 #define PT_DAR	41
 #define PT_DSISR 42
 #define PT_RESULT 43
+#define PT_DSCR 44
 #define PT_REGS_COUNT 44
 
 #define PT_FPR0	48	/* each FP reg occupies 2 slots in this space */
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index d4afccc..245c1b6 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -179,6 +179,30 @@  static int set_user_msr(struct task_struct *task, unsigned long msr)
 	return 0;
 }
 
+#ifdef CONFIG_PPC64
+static unsigned long get_user_dscr(struct task_struct *task)
+{
+	return task->thread.dscr;
+}
+
+static int set_user_dscr(struct task_struct *task, unsigned long dscr)
+{
+	task->thread.dscr = dscr;
+	task->thread.dscr_inherit = 1;
+	return 0;
+}
+#else
+static unsigned long get_user_dscr(struct task_struct *task)
+{
+	return -EIO;
+}
+
+static int set_user_dscr(struct task_struct *task, unsigned long dscr)
+{
+	return -EIO;
+}
+#endif
+
 /*
  * We prevent mucking around with the reserved area of trap
  * which are used internally by the kernel.
@@ -200,6 +224,9 @@  unsigned long ptrace_get_reg(struct task_struct *task, int regno)
 	if (regno == PT_MSR)
 		return get_user_msr(task);
 
+	if (regno == PT_DSCR)
+		return get_user_dscr(task);
+
 	if (regno < (sizeof(struct pt_regs) / sizeof(unsigned long)))
 		return ((unsigned long *)task->thread.regs)[regno];
 
@@ -218,6 +245,8 @@  int ptrace_put_reg(struct task_struct *task, int regno, unsigned long data)
 		return set_user_msr(task, data);
 	if (regno == PT_TRAP)
 		return set_user_trap(task, data);
+	if (regno == PT_DSCR)
+		return set_user_dscr(task, data);
 
 	if (regno <= PT_MAX_PUT_REG) {
 		((unsigned long *)task->thread.regs)[regno] = data;