linux-kernel - Re: [PATCH]KGTP (Linux Kernel debugger and tracer) lite patch for review

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Message-ID: <20120524150754.GF27374@one.firstfloor.org>
Date:	Thu, 24 May 2012 17:07:54 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Hui Zhu <teawater@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Geoff Levand <geoff@...radead.org>, jason.wessel@...driver.com
Subject: Re: [PATCH]KGTP (Linux Kernel debugger and tracer) lite patch for review

> I remove them from asm files, and add:
> #ifndef ULONGEST
> #define ULONGEST		uint64_t
> #endif
> #ifndef CORE_ADDR
> #define CORE_ADDR		unsigned long
> #endif
> in gtp.c
> Then if not need, the arch didn't define ULONGEST and CORE_ADDR for itself.

Which architecture needs it? Linux prefers to use "native" types.

> For example ARM and MIPS have a lot of special reg that cannot be converted 
> by a for loop.
> 
> After check the code the kgdb, I thought that good ways is use dbg_reg_def 
> of kgdb to convert the reg to gdb rsp format.  But use it directly will 
> make kgtp depend on kgdb.

That's fine. Code reuse is good. Code duplication is bad.

> What I thought is move this part of code out from kgdb, when kgdb or kgtp 
> need, select it too.  But I am not sure Jason is OK with that.

Just send a patch.

> >
> >>+     memcpy(&freg->regs, regs, sizeof(struct pt_regs));
> >>+#ifdef CONFIG_X86_32
> >>+     freg->regs.sp = (unsigned long)&regs->sp;
> >>+#endif       /* CONFIG_X86_32 */
> >>+#ifdef CONFIG_X86
> >>+     freg->regs.ip -= 1;
> >>+#endif       /* CONFIG_X86 */
> >
> >What is that for? - 1?
> 
> That is because when kprobe, the ip of X86 point will have a offset with 
> current ip.

But a kprobe is not necessarily one byte. e.g. a jumper probe is longer.

Anyways if that is really needed there should be some macros provided
by kprobes to adjust IP. If it's not there it needs to be added.
> >>+
> >>+     if (gtp_start)
> >>+             return -EBUSY;
> >
> >This is in a lot of places. Can you put it somewhere more central?
> 
> Sorry I don't understand this part.  Do you want I change all "struct 
> gtp_entry        *tpe;" to "struct gtp_entry *tpe;"?

I mean the if (gtp_start) return -EBUSY check.

> >
> >>+     pr_devel("gtp_gdbrsp_QT: %s\n", pkg);
> >>+
> >>+     if (strcmp("init", pkg) == 0)
> >>+             ret = gtp_gdbrsp_qtinit();
> >
> >This if cascade should be probably a table walk
> 
> I cannot find the examle about it in the Kernel, could you give me a 
> example?


struct cmd {
	char *name;
	int (*init)(void);
};

struct cmd cmds[] = {
	{ "init", gtp_xyz_init }
	...
	{} 
};

int i;
for (i = 0; cmds[i].name; i++)
	if (!strcmp(cmds[i].name, pkg))
		ret = cmds->init();


> >Ok so what lock protects this buffer?
> 
> No.  The gtp_frame_lock protects the vars that follow it:
> static int			gtp_frame_num;
> static char			*gtp_frame;
> static char			*gtp_frame_r_start;
> static char			*gtp_frame_w_start;
> static char			*gtp_frame_w_end;
> static char			*gtp_frame_r_cache;
> static int			gtp_frame_is_circular;
> It protects them all.
> 
> gtp_m_buffer is protected by gtp_rw_lock that I just add in new patch.

Then your comment was wrong/unclear?

> 
> 
> OK.  Add some introduce.  checkpatch is OK with it.

You must be using an old version?

# check for Kconfig help text having a real description
# Only applies when adding the entry originally, after that we do not have
# sufficient context to determine whether it is indeed long enough.
...
        WARN("CONFIG_DESCRIPTION",
                             "please write a paragraph that describes the config symbol fully\n" . $herecurr) if ($is_start && $is_end && $length < 4);

I wonder how you avoided that.

-Andi
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