[PATCH] ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls

[PATCH] ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls

[Sergei Trofimovich]

In https://bugs.gentoo.org/769614 Dmitry noticed that
`ptrace(PTRACE_GET_SYSCALL_INFO)` does not work for syscalls called
via glibc's syscall() wrapper.

ia64 has two ways to call syscalls from userspace: via `break` and via
`eps` instructions.

The difference is in stack layout:

1. `eps` creates simple stack frame: no locals, in{0..7} == out{0..8}
2. `break` uses userspace stack frame: may be locals (glibc provides
   one), in{0..7} == out{0..8}.

Both work fine in syscall handling cde itself.

But `ptrace(PTRACE_GET_SYSCALL_INFO)` uses unwind mechanism to
re-extract syscall arguments but it does not account for locals.

The change always skips locals registers. It should not change `eps`
path as kernel's handler already enforces locals=0 and fixes `break`.

Tested on v5.10 on rx3600 machine (ia64 9040 CPU).

CC: Oleg Nesterov <oleg@redhat.com>
CC: linux-ia64@vger.kernel.org
CC: linux-kernel@vger.kernel.org
CC: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Dmitry V. Levin <ldv@altlinux.org>
Bug: https://bugs.gentoo.org/769614
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
 arch/ia64/kernel/ptrace.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
index c3490ee2daa5..e14f5653393a 100644
--- a/arch/ia64/kernel/ptrace.c
+++ b/arch/ia64/kernel/ptrace.c
@@ -2013,27 +2013,39 @@ static void syscall_get_set_args_cb(struct unw_frame_info *info, void *data)
 {
 	struct syscall_get_set_args *args = data;
 	struct pt_regs *pt = args->regs;
-	unsigned long *krbs, cfm, ndirty;
+	unsigned long *krbs, cfm, ndirty, nlocals, nouts;
 	int i, count;
 
 	if (unw_unwind_to_user(info) < 0)
 		return;
 
+	/*
+	 * We get here via a few paths:
+	 * - break instruction: cfm is shared with caller.
+	 *   syscall args are in out= regs, locals are non-empty.
+	 * - epsinstruction: cfm is set by br.call
+	 *   locals don't exist.
+	 *
+	 * For both cases argguments are reachable in cfm.sof - cfm.sol.
+	 * CFM: [ ... | sor: 17..14 | sol : 13..7 | sof : 6..0 ]
+	 */
 	cfm = pt->cr_ifs;
+	nlocals = (cfm >> 7) & 0x7f; /* aka sol */
+	nouts = (cfm & 0x7f) - nlocals; /* aka sof - sol */
 	krbs = (unsigned long *)info->task + IA64_RBS_OFFSET/8;
 	ndirty = ia64_rse_num_regs(krbs, krbs + (pt->loadrs >> 19));
 
 	count = 0;
 	if (in_syscall(pt))
-		count = min_t(int, args->n, cfm & 0x7f);
+		count = min_t(int, args->n, nouts);
 
+	/* Iterate over outs. */
 	for (i = 0; i < count; i++) {
+		int j = ndirty + nlocals + i + args->i;
 		if (args->rw)
-			*ia64_rse_skip_regs(krbs, ndirty + i + args->i) =
-				args->args[i];
+			*ia64_rse_skip_regs(krbs, j) = args->args[i];
 		else
-			args->args[i] = *ia64_rse_skip_regs(krbs,
-				ndirty + i + args->i);
+			args->args[i] = *ia64_rse_skip_regs(krbs, j);
 	}
 
 	if (!args->rw) {
-- 
2.30.1

[PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[Sergei Trofimovich]

In https://bugs.gentoo.org/769614 Dmitry noticed that
`ptrace(PTRACE_GET_SYSCALL_INFO)` does not return error sign properly.

The bug is in mismatch between get/set errors:

static inline long syscall_get_error(struct task_struct *task,
                                     struct pt_regs *regs)
{
        return regs->r10 == -1 ? regs->r8:0;
}

static inline long syscall_get_return_value(struct task_struct *task,
                                            struct pt_regs *regs)
{
        return regs->r8;
}

static inline void syscall_set_return_value(struct task_struct *task,
                                            struct pt_regs *regs,
                                            int error, long val)
{
        if (error) {
                /* error < 0, but ia64 uses > 0 return value */
                regs->r8 = -error;
                regs->r10 = -1;
        } else {
                regs->r8 = val;
                regs->r10 = 0;
        }
}

Tested on v5.10 on rx3600 machine (ia64 9040 CPU).

CC: linux-ia64@vger.kernel.org
CC: linux-kernel@vger.kernel.org
CC: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Dmitry V. Levin <ldv@altlinux.org>
Bug: https://bugs.gentoo.org/769614
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
 arch/ia64/include/asm/syscall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/ia64/include/asm/syscall.h b/arch/ia64/include/asm/syscall.h
index 6c6f16e409a8..0d23c0049301 100644
--- a/arch/ia64/include/asm/syscall.h
+++ b/arch/ia64/include/asm/syscall.h
@@ -32,7 +32,7 @@ static inline void syscall_rollback(struct task_struct *task,
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {
-	return regs->r10 == -1 ? regs->r8:0;
+	return regs->r10 == -1 ? -regs->r8:0;
 }
 
 static inline long syscall_get_return_value(struct task_struct *task,
-- 
2.30.1

Re: [PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[John Paul Adrian Glaubitz]

Hi Sergei!

On 2/21/21 1:25 AM, Sergei Trofimovich wrote:
> In https://bugs.gentoo.org/769614 Dmitry noticed that
> `ptrace(PTRACE_GET_SYSCALL_INFO)` does not return error sign properly.
> (...)

Do these two patches unbreak gdb on ia64?

And have you, by any chance, managed to get the hpsa driver working again?

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@debian.org
`. `'   Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913

Re: [PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[Sergei Trofimovich]

On Sun, 21 Feb 2021 10:21:56 +0100
John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> wrote:

> Hi Sergei!
> 
> On 2/21/21 1:25 AM, Sergei Trofimovich wrote:
> > In https://bugs.gentoo.org/769614 Dmitry noticed that
> > `ptrace(PTRACE_GET_SYSCALL_INFO)` does not return error sign properly.
> > (...)  
> 
> Do these two patches unbreak gdb on ia64?

gdb was somewhat working on ia64 for Gentoo. strace was the main
impacted here.

But I did not try anything complicated recently. Anything specific that
breaks for you?

$ uname -r
5.10.0
(even without the patches above)

$ cat c.c
int main(){}
$ gcc c.c -o a -ggdb3
$ gdb --quiet ./a
Reading symbols from ./a...
(gdb) start
Temporary breakpoint 1 at 0x7f2: file c.c, line 1.
Starting program: /home/slyfox/a
Failed to read a valid object file image from memory.

Temporary breakpoint 1, main () at c.c:1
1	int main(){}
(gdb) disassemble
Dump of assembler code for function main:
   0x20000008000007f0 <+0>:	[MII]       mov r2=r12
   0x20000008000007f1 <+1>:	            mov r14=r0;;
=> 0x20000008000007f2 <+2>:	            mov r8=r14
   0x2000000800000800 <+16>:	[MIB]       mov r12=r2
   0x2000000800000801 <+17>:	            nop.i 0x0
   0x2000000800000802 <+18>:	            br.ret.sptk.many b0;;
End of assembler dump.
(gdb) break *0x2000000800000800
Breakpoint 2 at 0x2000000800000800: file c.c, line 1.
(gdb) continue
Continuing.

Breakpoint 2, 0x2000000800000800 in main () at c.c:1
1	int main(){}

Looks ok for minor stuff.

> And have you, by any chance, managed to get the hpsa driver working again?

v5.10 seems to boot off hpsa just fine without extra patches:
  14:01.0 RAID bus controller: Hewlett-Packard Company Smart Array P600
	Subsystem: Hewlett-Packard Company 3 Gb/s SAS RAID
	Kernel driver in use: hpsa

v5.11 does not boot yet. Kernel does not see some files while boots after init is
started  (but I'm not sure it's a block device problem). Bisecting now why.

-- 

  Sergei

Re: [PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[Sergei Trofimovich]

On Sun, 21 Feb 2021 00:25:54 +0000
Sergei Trofimovich <slyfox@gentoo.org> wrote:

> In https://bugs.gentoo.org/769614 Dmitry noticed that
> `ptrace(PTRACE_GET_SYSCALL_INFO)` does not return error sign properly.
> 
> The bug is in mismatch between get/set errors:
> 
> static inline long syscall_get_error(struct task_struct *task,
>                                      struct pt_regs *regs)
> {
>         return regs->r10 == -1 ? regs->r8:0;
> }
> 
> static inline long syscall_get_return_value(struct task_struct *task,
>                                             struct pt_regs *regs)
> {
>         return regs->r8;
> }
> 
> static inline void syscall_set_return_value(struct task_struct *task,
>                                             struct pt_regs *regs,
>                                             int error, long val)
> {
>         if (error) {
>                 /* error < 0, but ia64 uses > 0 return value */
>                 regs->r8 = -error;
>                 regs->r10 = -1;
>         } else {
>                 regs->r8 = val;
>                 regs->r10 = 0;
>         }
> }
> 
> Tested on v5.10 on rx3600 machine (ia64 9040 CPU).
> 
> CC: linux-ia64@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> CC: Andrew Morton <akpm@linux-foundation.org>
> Reported-by: Dmitry V. Levin <ldv@altlinux.org>
> Bug: https://bugs.gentoo.org/769614
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
>  arch/ia64/include/asm/syscall.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/ia64/include/asm/syscall.h b/arch/ia64/include/asm/syscall.h
> index 6c6f16e409a8..0d23c0049301 100644
> --- a/arch/ia64/include/asm/syscall.h
> +++ b/arch/ia64/include/asm/syscall.h
> @@ -32,7 +32,7 @@ static inline void syscall_rollback(struct task_struct *task,
>  static inline long syscall_get_error(struct task_struct *task,
>  				     struct pt_regs *regs)
>  {
> -	return regs->r10 == -1 ? regs->r8:0;
> +	return regs->r10 == -1 ? -regs->r8:0;
>  }
>  
>  static inline long syscall_get_return_value(struct task_struct *task,
> -- 
> 2.30.1
> 

Andrew, would it be fine to pass it through misc tree?
Or should it go through Oleg as it's mostly about ptrace?

-- 

  Sergei

Re: [PATCH] ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls

[Sergei Trofimovich]

On Sun, 21 Feb 2021 00:25:53 +0000
Sergei Trofimovich <slyfox@gentoo.org> wrote:

> In https://bugs.gentoo.org/769614 Dmitry noticed that
> `ptrace(PTRACE_GET_SYSCALL_INFO)` does not work for syscalls called
> via glibc's syscall() wrapper.
> 
> ia64 has two ways to call syscalls from userspace: via `break` and via
> `eps` instructions.
> 
> The difference is in stack layout:
> 
> 1. `eps` creates simple stack frame: no locals, in{0..7} == out{0..8}
> 2. `break` uses userspace stack frame: may be locals (glibc provides
>    one), in{0..7} == out{0..8}.
> 
> Both work fine in syscall handling cde itself.
> 
> But `ptrace(PTRACE_GET_SYSCALL_INFO)` uses unwind mechanism to
> re-extract syscall arguments but it does not account for locals.
> 
> The change always skips locals registers. It should not change `eps`
> path as kernel's handler already enforces locals=0 and fixes `break`.
> 
> Tested on v5.10 on rx3600 machine (ia64 9040 CPU).
> 
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: linux-ia64@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> CC: Andrew Morton <akpm@linux-foundation.org>
> Reported-by: Dmitry V. Levin <ldv@altlinux.org>
> Bug: https://bugs.gentoo.org/769614
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
>  arch/ia64/kernel/ptrace.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
> index c3490ee2daa5..e14f5653393a 100644
> --- a/arch/ia64/kernel/ptrace.c
> +++ b/arch/ia64/kernel/ptrace.c
> @@ -2013,27 +2013,39 @@ static void syscall_get_set_args_cb(struct unw_frame_info *info, void *data)
>  {
>  	struct syscall_get_set_args *args = data;
>  	struct pt_regs *pt = args->regs;
> -	unsigned long *krbs, cfm, ndirty;
> +	unsigned long *krbs, cfm, ndirty, nlocals, nouts;
>  	int i, count;
>  
>  	if (unw_unwind_to_user(info) < 0)
>  		return;
>  
> +	/*
> +	 * We get here via a few paths:
> +	 * - break instruction: cfm is shared with caller.
> +	 *   syscall args are in out= regs, locals are non-empty.
> +	 * - epsinstruction: cfm is set by br.call
> +	 *   locals don't exist.
> +	 *
> +	 * For both cases argguments are reachable in cfm.sof - cfm.sol.
> +	 * CFM: [ ... | sor: 17..14 | sol : 13..7 | sof : 6..0 ]
> +	 */
>  	cfm = pt->cr_ifs;
> +	nlocals = (cfm >> 7) & 0x7f; /* aka sol */
> +	nouts = (cfm & 0x7f) - nlocals; /* aka sof - sol */
>  	krbs = (unsigned long *)info->task + IA64_RBS_OFFSET/8;
>  	ndirty = ia64_rse_num_regs(krbs, krbs + (pt->loadrs >> 19));
>  
>  	count = 0;
>  	if (in_syscall(pt))
> -		count = min_t(int, args->n, cfm & 0x7f);
> +		count = min_t(int, args->n, nouts);
>  
> +	/* Iterate over outs. */
>  	for (i = 0; i < count; i++) {
> +		int j = ndirty + nlocals + i + args->i;
>  		if (args->rw)
> -			*ia64_rse_skip_regs(krbs, ndirty + i + args->i) =
> -				args->args[i];
> +			*ia64_rse_skip_regs(krbs, j) = args->args[i];
>  		else
> -			args->args[i] = *ia64_rse_skip_regs(krbs,
> -				ndirty + i + args->i);
> +			args->args[i] = *ia64_rse_skip_regs(krbs, j);
>  	}
>  
>  	if (!args->rw) {
> -- 
> 2.30.1
> 

Andrew, would it be fine to pass it through misc tree?
Or should it go through Oleg as it's about ptrace?

-- 

  Sergei

Re: [PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[Oleg Nesterov]

On 03/02, Sergei Trofimovich wrote:
>
> > --- a/arch/ia64/include/asm/syscall.h
> > +++ b/arch/ia64/include/asm/syscall.h
> > @@ -32,7 +32,7 @@ static inline void syscall_rollback(struct task_struct *task,
> >  static inline long syscall_get_error(struct task_struct *task,
> >  				     struct pt_regs *regs)
> >  {
> > -	return regs->r10 == -1 ? regs->r8:0;
> > +	return regs->r10 == -1 ? -regs->r8:0;
> >  }
> >
> >  static inline long syscall_get_return_value(struct task_struct *task,
> > --
> > 2.30.1
> >
>
> Andrew, would it be fine to pass it through misc tree?
> Or should it go through Oleg as it's mostly about ptrace?

We usually route ptrace fixes via mm tree.

But this fix and another patch from you "ia64: fix ia64_syscall_get_set_arguments()
for break-based syscalls" look very much ia64 specific. I don't think it's actually
about ptrace, and I didn't even try to review these patches because I do not
understand this low level ia64 code.

Can it be routed via ia64 tree? Add Tony and Fenghua...

Oleg.

Re: [PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[Dmitry V. Levin]

On Wed, Mar 03, 2021 at 03:30:19PM +0100, Oleg Nesterov wrote:
> On 03/02, Sergei Trofimovich wrote:
> >
> > > --- a/arch/ia64/include/asm/syscall.h
> > > +++ b/arch/ia64/include/asm/syscall.h
> > > @@ -32,7 +32,7 @@ static inline void syscall_rollback(struct task_struct *task,
> > >  static inline long syscall_get_error(struct task_struct *task,
> > >  				     struct pt_regs *regs)
> > >  {
> > > -	return regs->r10 == -1 ? regs->r8:0;
> > > +	return regs->r10 == -1 ? -regs->r8:0;
> > >  }
> > >
> > >  static inline long syscall_get_return_value(struct task_struct *task,
> > > --
> > > 2.30.1
> > >
> >
> > Andrew, would it be fine to pass it through misc tree?
> > Or should it go through Oleg as it's mostly about ptrace?
> 
> We usually route ptrace fixes via mm tree.
> 
> But this fix and another patch from you "ia64: fix ia64_syscall_get_set_arguments()
> for break-based syscalls" look very much ia64 specific. I don't think it's actually
> about ptrace, and I didn't even try to review these patches because I do not
> understand this low level ia64 code.
> 
> Can it be routed via ia64 tree? Add Tony and Fenghua...

Apparently [1], ia64 architecture is now orphaned, so we don't have this
option anymore.

[1] https://git.kernel.org/torvalds/c/96ec72a3425d1515b69b7f9dc34a4a6ce5862a37


-- 
ldv

Re: [PATCH] ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign

[Dmitry V. Levin]

On Sun, Feb 21, 2021 at 12:25:54AM +0000, Sergei Trofimovich wrote:
> In https://bugs.gentoo.org/769614 Dmitry noticed that
> `ptrace(PTRACE_GET_SYSCALL_INFO)` does not return error sign properly.
> 
> The bug is in mismatch between get/set errors:
> 
> static inline long syscall_get_error(struct task_struct *task,
>                                      struct pt_regs *regs)
> {
>         return regs->r10 == -1 ? regs->r8:0;
> }
> 
> static inline long syscall_get_return_value(struct task_struct *task,
>                                             struct pt_regs *regs)
> {
>         return regs->r8;
> }
> 
> static inline void syscall_set_return_value(struct task_struct *task,
>                                             struct pt_regs *regs,
>                                             int error, long val)
> {
>         if (error) {
>                 /* error < 0, but ia64 uses > 0 return value */
>                 regs->r8 = -error;
>                 regs->r10 = -1;
>         } else {
>                 regs->r8 = val;
>                 regs->r10 = 0;
>         }
> }
> 
> Tested on v5.10 on rx3600 machine (ia64 9040 CPU).
> 
> CC: linux-ia64@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> CC: Andrew Morton <akpm@linux-foundation.org>
> Reported-by: Dmitry V. Levin <ldv@altlinux.org>
> Bug: https://bugs.gentoo.org/769614
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
>  arch/ia64/include/asm/syscall.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/ia64/include/asm/syscall.h b/arch/ia64/include/asm/syscall.h
> index 6c6f16e409a8..0d23c0049301 100644
> --- a/arch/ia64/include/asm/syscall.h
> +++ b/arch/ia64/include/asm/syscall.h
> @@ -32,7 +32,7 @@ static inline void syscall_rollback(struct task_struct *task,
>  static inline long syscall_get_error(struct task_struct *task,
>  				     struct pt_regs *regs)
>  {
> -	return regs->r10 == -1 ? regs->r8:0;
> +	return regs->r10 == -1 ? -regs->r8:0;
>  }
>  
>  static inline long syscall_get_return_value(struct task_struct *task,

Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>


-- 
ldv

Re: [PATCH] ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls

[Dmitry V. Levin]

On Sun, Feb 21, 2021 at 12:25:53AM +0000, Sergei Trofimovich wrote:
> In https://bugs.gentoo.org/769614 Dmitry noticed that
> `ptrace(PTRACE_GET_SYSCALL_INFO)` does not work for syscalls called
> via glibc's syscall() wrapper.
> 
> ia64 has two ways to call syscalls from userspace: via `break` and via
> `eps` instructions.
> 
> The difference is in stack layout:
> 
> 1. `eps` creates simple stack frame: no locals, in{0..7} == out{0..8}
> 2. `break` uses userspace stack frame: may be locals (glibc provides
>    one), in{0..7} == out{0..8}.
> 
> Both work fine in syscall handling cde itself.
> 
> But `ptrace(PTRACE_GET_SYSCALL_INFO)` uses unwind mechanism to
> re-extract syscall arguments but it does not account for locals.
> 
> The change always skips locals registers. It should not change `eps`
> path as kernel's handler already enforces locals=0 and fixes `break`.
> 
> Tested on v5.10 on rx3600 machine (ia64 9040 CPU).
> 
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: linux-ia64@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> CC: Andrew Morton <akpm@linux-foundation.org>
> Reported-by: Dmitry V. Levin <ldv@altlinux.org>
> Bug: https://bugs.gentoo.org/769614
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
>  arch/ia64/kernel/ptrace.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
> index c3490ee2daa5..e14f5653393a 100644
> --- a/arch/ia64/kernel/ptrace.c
> +++ b/arch/ia64/kernel/ptrace.c
> @@ -2013,27 +2013,39 @@ static void syscall_get_set_args_cb(struct unw_frame_info *info, void *data)
>  {
>  	struct syscall_get_set_args *args = data;
>  	struct pt_regs *pt = args->regs;
> -	unsigned long *krbs, cfm, ndirty;
> +	unsigned long *krbs, cfm, ndirty, nlocals, nouts;
>  	int i, count;
>  
>  	if (unw_unwind_to_user(info) < 0)
>  		return;
>  
> +	/*
> +	 * We get here via a few paths:
> +	 * - break instruction: cfm is shared with caller.
> +	 *   syscall args are in out= regs, locals are non-empty.
> +	 * - epsinstruction: cfm is set by br.call
> +	 *   locals don't exist.

typo: epsinstruction

> +	 *
> +	 * For both cases argguments are reachable in cfm.sof - cfm.sol.

typo: argguments

> +	 * CFM: [ ... | sor: 17..14 | sol : 13..7 | sof : 6..0 ]
> +	 */
>  	cfm = pt->cr_ifs;
> +	nlocals = (cfm >> 7) & 0x7f; /* aka sol */
> +	nouts = (cfm & 0x7f) - nlocals; /* aka sof - sol */
>  	krbs = (unsigned long *)info->task + IA64_RBS_OFFSET/8;
>  	ndirty = ia64_rse_num_regs(krbs, krbs + (pt->loadrs >> 19));
>  
>  	count = 0;
>  	if (in_syscall(pt))
> -		count = min_t(int, args->n, cfm & 0x7f);
> +		count = min_t(int, args->n, nouts);
>  
> +	/* Iterate over outs. */
>  	for (i = 0; i < count; i++) {
> +		int j = ndirty + nlocals + i + args->i;
>  		if (args->rw)
> -			*ia64_rse_skip_regs(krbs, ndirty + i + args->i) =
> -				args->args[i];
> +			*ia64_rse_skip_regs(krbs, j) = args->args[i];
>  		else
> -			args->args[i] = *ia64_rse_skip_regs(krbs,
> -				ndirty + i + args->i);
> +			args->args[i] = *ia64_rse_skip_regs(krbs, j);
>  	}
>  
>  	if (!args->rw) {

This stuff is too ia64 specific, so I cannot properly review this patch,
but it definitely fixes ia64 PTRACE_GET_SYSCALL_INFO on entering syscall.


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