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Message-ID: <20130326120602.GA20399@linux.vnet.ibm.com>
Date: Tue, 26 Mar 2013 17:36:02 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc: lkml <linux-kernel@...r.kernel.org>, oleg@...hat.com,
benh@...nel.crashing.org, ppcdev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 1/4] uprobes: add trap variant helper
* Ananth N Mavinakayanahalli <ananth@...ibm.com> [2013-03-22 20:46:27]:
> From: Ananth N Mavinakayanahalli <ananth@...ibm.com>
>
> Some architectures like powerpc have multiple variants of the trap
> instruction. Introduce an additional helper is_trap_insn() for run-time
> handling of non-uprobe traps on such architectures.
>
> While there, change is_swbp_at_addr() to is_trap_at_addr() for reading
> clarity.
>
> With this change, the uprobe registration path will supercede any trap
> instruction inserted at the requested location, while taking care of
> delivering the SIGTRAP for cases where the trap notification came in
> for an address without a uprobe. See [1] for a more detailed explanation.
>
> [1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2013-March/104771.html
>
> This change was suggested by Oleg Nesterov.
>
> Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> ---
> include/linux/uprobes.h | 1 +
> kernel/events/uprobes.c | 32 ++++++++++++++++++++++++++++----
> 2 files changed, 29 insertions(+), 4 deletions(-)
>
> Index: linux-3.9-rc3/include/linux/uprobes.h
> ===================================================================
> --- linux-3.9-rc3.orig/include/linux/uprobes.h
> +++ linux-3.9-rc3/include/linux/uprobes.h
> @@ -100,6 +100,7 @@ struct uprobes_state {
> extern int __weak set_swbp(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long vaddr);
> extern int __weak set_orig_insn(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long vaddr);
> extern bool __weak is_swbp_insn(uprobe_opcode_t *insn);
> +extern bool __weak is_trap_insn(uprobe_opcode_t *insn);
> extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
> extern int uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, bool);
> extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
> Index: linux-3.9-rc3/kernel/events/uprobes.c
> ===================================================================
> --- linux-3.9-rc3.orig/kernel/events/uprobes.c
> +++ linux-3.9-rc3/kernel/events/uprobes.c
> @@ -173,6 +173,20 @@ bool __weak is_swbp_insn(uprobe_opcode_t
> return *insn == UPROBE_SWBP_INSN;
> }
>
> +/**
> + * is_trap_insn - check if instruction is breakpoint instruction.
> + * @insn: instruction to be checked.
> + * Default implementation of is_trap_insn
> + * Returns true if @insn is a breakpoint instruction.
> + *
> + * This function is needed for the case where an architecture has multiple
> + * trap instructions (like powerpc).
> + */
> +bool __weak is_trap_insn(uprobe_opcode_t *insn)
> +{
> + return is_swbp_insn(insn);
> +}
> +
> static void copy_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *opcode)
> {
> void *kaddr = kmap_atomic(page);
> @@ -185,6 +199,15 @@ static int verify_opcode(struct page *pa
> uprobe_opcode_t old_opcode;
> bool is_swbp;
>
> + /*
> + * Note: We only check if the old_opcode is UPROBE_SWBP_INSN here.
> + * We do not check if it is any other 'trap variant' which could
> + * be conditional trap instruction such as the one powerpc supports.
> + *
> + * The logic is that we do not care if the underlying instruction
> + * is a trap variant; uprobes always wins over any other (gdb)
> + * breakpoint.
> + */
> copy_opcode(page, vaddr, &old_opcode);
> is_swbp = is_swbp_insn(&old_opcode);
>
> @@ -204,7 +227,7 @@ static int verify_opcode(struct page *pa
> * Expect the breakpoint instruction to be the smallest size instruction for
> * the architecture. If an arch has variable length instruction and the
> * breakpoint instruction is not of the smallest length instruction
> - * supported by that architecture then we need to modify is_swbp_at_addr and
> + * supported by that architecture then we need to modify is_trap_at_addr and
> * write_opcode accordingly. This would never be a problem for archs that
> * have fixed length instructions.
> */
> @@ -1431,7 +1454,7 @@ static void mmf_recalc_uprobes(struct mm
> clear_bit(MMF_HAS_UPROBES, &mm->flags);
> }
>
> -static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
> +static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
> {
> struct page *page;
> uprobe_opcode_t opcode;
> @@ -1452,7 +1475,8 @@ static int is_swbp_at_addr(struct mm_str
> copy_opcode(page, vaddr, &opcode);
> put_page(page);
> out:
> - return is_swbp_insn(&opcode);
> + /* This needs to return true for any variant of the trap insn */
> + return is_trap_insn(&opcode);
> }
>
> static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
> @@ -1472,7 +1496,7 @@ static struct uprobe *find_active_uprobe
> }
>
> if (!uprobe)
> - *is_swbp = is_swbp_at_addr(mm, bp_vaddr);
> + *is_swbp = is_trap_at_addr(mm, bp_vaddr);
> } else {
> *is_swbp = -EFAULT;
> }
--
Thanks and Regards
Srikar Dronamraju
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