[1/2] uprobes: Pass probed vaddr to arch_uprobe_analyze_insn()

From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

On RISC architectures like powerpc, instructions are fixed size.
Instruction analysis on such platforms is just a matter of (insn % 4).
Pass the vaddr at which the uprobe is to be inserted so that
arch_uprobe_analyze_insn() can flag misaligned registration requests.

Signed-off-by: Ananth N Mavinakaynahalli <ananth@in.ibm.com>
---
 arch/x86/include/asm/uprobes.h |    2 +-
 arch/x86/kernel/uprobes.c      |    3 ++-
 kernel/events/uprobes.c        |    2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

On Wed, 2012-06-06 at 14:49 +0530, Ananth N Mavinakayanahalli wrote:
> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, loff_t vaddr)

Don't we traditionally use unsigned long to pass vaddrs?

On Wed, Jun 06, 2012 at 11:23:52AM +0200, Peter Zijlstra wrote:
> On Wed, 2012-06-06 at 14:49 +0530, Ananth N Mavinakayanahalli wrote:
> > +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, loff_t vaddr)
> 
> Don't we traditionally use unsigned long to pass vaddrs?

Right. But the vaddr we pass here is vma_info->vaddr which is loff_t.
I guess I should've made that clear in the patch description.

Ananth

* Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote:

> On Wed, Jun 06, 2012 at 11:23:52AM +0200, Peter Zijlstra wrote:
> > On Wed, 2012-06-06 at 14:49 +0530, Ananth N Mavinakayanahalli wrote:
> > > +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, loff_t vaddr)
> > 
> > Don't we traditionally use unsigned long to pass vaddrs?
> 
> Right. But the vaddr we pass here is vma_info->vaddr which is loff_t.
> I guess I should've made that clear in the patch description.

Why not fix struct vma_info's vaddr type?

Thanks,

	Ingo

On Wed, Jun 06, 2012 at 11:40:15AM +0200, Ingo Molnar wrote:
> 
> * Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote:
> 
> > On Wed, Jun 06, 2012 at 11:23:52AM +0200, Peter Zijlstra wrote:
> > > On Wed, 2012-06-06 at 14:49 +0530, Ananth N Mavinakayanahalli wrote:
> > > > +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, loff_t vaddr)
> > > 
> > > Don't we traditionally use unsigned long to pass vaddrs?
> > 
> > Right. But the vaddr we pass here is vma_info->vaddr which is loff_t.
> > I guess I should've made that clear in the patch description.
> 
> Why not fix struct vma_info's vaddr type?

Agreed. Will fix and send v2.

Ananth

* Ingo Molnar <mingo@kernel.org> [2012-06-06 11:40:15]:

> 
> * Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote:
> 
> > On Wed, Jun 06, 2012 at 11:23:52AM +0200, Peter Zijlstra wrote:
> > > On Wed, 2012-06-06 at 14:49 +0530, Ananth N Mavinakayanahalli wrote:
> > > > +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, loff_t vaddr)
> > > 
> > > Don't we traditionally use unsigned long to pass vaddrs?
> > 
> > Right. But the vaddr we pass here is vma_info->vaddr which is loff_t.
> > I guess I should've made that clear in the patch description.
> 
> Why not fix struct vma_info's vaddr type?
> 

Calculating and comparing vaddr results either uses variables of type loff_t. 
To avoid typecasting and avoid overflow at each of these places, we used
loff_t. 

Ananth, install_breakpoint() already has a variable of type addr of type
unsigned long.  Why dont you use addr instead of vaddr.

On 06/06, Ananth N Mavinakayanahalli wrote:
>
> From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
>
> On RISC architectures like powerpc, instructions are fixed size.
> Instruction analysis on such platforms is just a matter of (insn % 4).
> Pass the vaddr at which the uprobe is to be inserted so that
> arch_uprobe_analyze_insn() can flag misaligned registration requests.

And the next patch checks "vaddr & 0x03".

But why do you need this new arg? arch_uprobe_analyze_insn() could
check "container_of(auprobe, struct uprobe, arch)->offset & 0x3" with
the same effect, no? vm_start/vm_pgoff are obviously page-aligned.

Oleg.

* Oleg Nesterov <oleg@redhat.com> [2012-06-06 17:08:48]:

> On 06/06, Ananth N Mavinakayanahalli wrote:
> >
> > From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> >
> > On RISC architectures like powerpc, instructions are fixed size.
> > Instruction analysis on such platforms is just a matter of (insn % 4).
> > Pass the vaddr at which the uprobe is to be inserted so that
> > arch_uprobe_analyze_insn() can flag misaligned registration requests.
> 
> And the next patch checks "vaddr & 0x03".
> 
> But why do you need this new arg? arch_uprobe_analyze_insn() could
> check "container_of(auprobe, struct uprobe, arch)->offset & 0x3" with
> the same effect, no? vm_start/vm_pgoff are obviously page-aligned.
> 

We cant use container_of because we moved the definition for struct
uprobe to kernel/events/uprobe.c. This was possible before when struct
uprobe definition was in include/uprobes.h

On Wed, Jun 06, 2012 at 05:14:23PM +0530, Srikar Dronamraju wrote:
> * Ingo Molnar <mingo@kernel.org> [2012-06-06 11:40:15]:
> 
> > 
> > * Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote:
> > 
> > > On Wed, Jun 06, 2012 at 11:23:52AM +0200, Peter Zijlstra wrote:
> > > > On Wed, 2012-06-06 at 14:49 +0530, Ananth N Mavinakayanahalli wrote:
> > > > > +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, loff_t vaddr)
> > > > 
> > > > Don't we traditionally use unsigned long to pass vaddrs?
> > > 
> > > Right. But the vaddr we pass here is vma_info->vaddr which is loff_t.
> > > I guess I should've made that clear in the patch description.
> > 
> > Why not fix struct vma_info's vaddr type?
> > 
> 
> Calculating and comparing vaddr results either uses variables of type loff_t. 
> To avoid typecasting and avoid overflow at each of these places, we used
> loff_t. 
> 
> Ananth, install_breakpoint() already has a variable of type addr of type
> unsigned long.  Why dont you use addr instead of vaddr. 

Ok, makes sense. I'll change it in v2.

Ananth