linux-kernel - Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

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Date:	Mon, 25 Nov 2013 15:59:20 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei\(Jovi\)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

Hi Oleg,

On Tue, 12 Nov 2013 17:00:01 +0900, Namhyung Kim wrote:
> For @+addr syntax: user-space uses relative symbol address from a loaded
>                    base address and kernel calculates the base address
>                    using "current->utask->vaddr - tu->offset".

I tried this approach and realized that current->utask is not set or has
an invalid vaddr when handler_chain() is called.  So I had to apply
following patch and it seems to work well for me.  Could you confirm it?

Thanks,
Namhyung


diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ad8e1bdca70e..e63748d3520e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1456,7 +1456,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
 
 /* Prepare to single-step probed instruction out of line. */
 static int
-pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
+pre_ssout(struct uprobe *uprobe, struct pt_regs *regs)
 {
 	struct uprobe_task *utask;
 	unsigned long xol_vaddr;
@@ -1471,7 +1471,6 @@ pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
 		return -ENOMEM;
 
 	utask->xol_vaddr = xol_vaddr;
-	utask->vaddr = bp_vaddr;
 
 	err = arch_uprobe_pre_xol(&uprobe->arch, regs);
 	if (unlikely(err)) {
@@ -1701,6 +1700,7 @@ static bool handle_trampoline(struct pt_regs *regs)
 static void handle_swbp(struct pt_regs *regs)
 {
 	struct uprobe *uprobe;
+	struct uprobe_task *utask;
 	unsigned long bp_vaddr;
 	int uninitialized_var(is_swbp);
 
@@ -1744,11 +1744,17 @@ static void handle_swbp(struct pt_regs *regs)
 	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
 		goto out;
 
+	utask = get_utask();
+	if (!utask)
+		goto out;
+
+	utask->vaddr = bp_vaddr;
+
 	handler_chain(uprobe, regs);
 	if (can_skip_sstep(uprobe, regs))
 		goto out;
 
-	if (!pre_ssout(uprobe, regs, bp_vaddr))
+	if (!pre_ssout(uprobe, regs))
 		return;
 
 	/* can_skip_sstep() succeeded, or restart if can't singlestep */
--
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