[PATCH] uprobes: introduce arch_uprobe->ixol

[oleg@redhat.com (Oleg Nesterov)]

On 10/29, Oleg Nesterov wrote:
>
> David. Perhaps we can avoid the new hook altogether? What if we do
> the simple change below (it ignores powerpc) ?
>
> Then arm can add "unsigned long ixol[2]" into its arch_uprobe, and
> arch_uprobe_analyze_insn() can initialize this member correctly.
>
> What do you think?

Seriouly, how about the patch below?

In fact, given that you are going to reimplement set_swbp/orig_insn,
the new member is not strictly needed (afaics). But it looks more
clear this way, and we need s/MAX_UINSN_BYTES/sizeof()/ anyway.

Oleg.
---

Subject: [PATCH] uprobes: introduce arch_uprobe->ixol

Currently xol_get_insn_slot() assumes that we should simply copy
arch_uprobe->insn[] which is (ignoring arch_uprobe_analyze_insn)
just the copy of the original insn.

This is not true for arm which needs to create another insn to
execute it out-of-line.

So this patch simply adds the new member, ->ixol into the union.
This doesn't make any difference for x86 and powerpc, but arm
can divorce insn/ixol and initialize the correct xol insn in
arch_uprobe_analyze_insn().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/powerpc/include/asm/uprobes.h |    1 +
 arch/x86/include/asm/uprobes.h     |    5 ++++-
 kernel/events/uprobes.c            |    3 ++-
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/uprobes.h b/arch/powerpc/include/asm/uprobes.h
index 2301602..541fd6f 100644
--- a/arch/powerpc/include/asm/uprobes.h
+++ b/arch/powerpc/include/asm/uprobes.h
@@ -37,6 +37,7 @@ typedef ppc_opcode_t uprobe_opcode_t;
 struct arch_uprobe {
 	union {
 		u8	insn[MAX_UINSN_BYTES];
+		u8	ixol[MAX_UINSN_BYTES];
 		u32	ainsn;
 	};
 };
diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 6e51979..2a24180 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -35,7 +35,10 @@ typedef u8 uprobe_opcode_t;
 
 struct arch_uprobe {
 	u16				fixups;
-	u8				insn[MAX_UINSN_BYTES];
+	union {
+		u8			insn[MAX_UINSN_BYTES];
+		u8			ixol[MAX_UINSN_BYTES];
+	};
 #ifdef CONFIG_X86_64
 	unsigned long			rip_rela_target_address;
 #endif
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ad8e1bd..6aef5ad 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1256,7 +1256,8 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 		return 0;
 
 	/* Initialize the slot */
-	copy_to_page(area->page, xol_vaddr, uprobe->arch.insn, MAX_UINSN_BYTES);
+	copy_to_page(area->page, xol_vaddr,
+			uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
 	/*
 	 * We probably need flush_icache_user_range() but it needs vma.
 	 * This should work on supported architectures too.
-- 
1.5.5.1