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From: Ingo Molnar <mingo@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jon Medhurst <tixy@linaro.org>, Will Deacon <will.deacon@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	"Tobin C . Harding" <me@tobin.cc>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Thomas Richter <tmricht@linux.ibm.com>,
	akpm@linux-foundation.org, acme@kernel.org, rostedt@goodmis.org,
	brueckner@linux.vnet.ibm.com, schwidefsky@de.ibm.com,
	stable@vger.kernel.org
Subject: Re: [PATCH v3 2/7] kprobes: Show blacklist addresses as same as kallsyms does
Date: Fri, 27 Apr 2018 09:14:17 +0200	[thread overview]
Message-ID: <20180427071417.lq4swylywht7mdy7@gmail.com> (raw)
In-Reply-To: <152481123945.22588.459569704440210836.stgit@devbox>


* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> +	/*
> +	 * As long as kallsyms shows the address, kprobes blacklist also
> +	 * show it, Or, it shows null address and symbol.
> +	 */

Please _read_ the comments you write!

In which universe does a capitalized 'Or' make sense, even if we ignore the 
various other spelling mistakes?

Also, that sentence is unnecessarily complex, just say this:

> +	/*
> +	 * If /proc/kallsyms is not showing kernel addresses then we won't show 
> +      * them here either:
> +	 */

But I'm unhappy about the messy typing and the messy code flow:

+       void *start = (void *)ent->start_addr, *end = (void *)ent->end_addr;

+       /*
+        * As long as kallsyms shows the address, kprobes blacklist also
+        * show it, Or, it shows null address and symbol.
+        */
+       if (!kallsyms_show_value())
+               start = end = NULL;
+
+       seq_printf(m, "0x%px-0x%px\t%ps\n", start, end,
+                  (void *)ent->start_addr);


All three 'void *' type casts here are due to the bad type choices here:

struct kprobe_blacklist_entry {
        struct list_head list;
        unsigned long start_addr;
        unsigned long end_addr;
};

The natural type of ->start_addr and ->end_addr is 'void *', AFAICS this would 
remove some other type casts from the kprobes code as well, such as from the 
arch_deref_entry_point()...

But the whole code flow introduced by this patch is messy as hell as well.
Why cannot this do the obvious thing:

	if (!kallsyms_show_value())
		seq_printf(m, "0x%px-0x%px\t%ps\n", NULL, NULL, ent->start_addr);
	else
		seq_printf(m, "0x%px-0x%px\t%ps\n", ent->start_addr, ent->end_addr, ent->start_addr);

?

This variant eliminates the unnecessary complication over local variables and 
makes it abundantly clear what gets printed and how.

( Note that the kprobe_blacklist_entry type cleanup should still be done, 
  regardless of code flow choices. )

Thanks,

	Ingo

  reply	other threads:[~2018-04-27  7:14 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-27  6:39 [PATCH v3 0/7] kprobes: Fix %p in kprobes Masami Hiramatsu
2018-04-27  6:40 ` [PATCH v3 1/7] kprobes: Make blacklist root user read only Masami Hiramatsu
2018-04-27  6:56   ` Greg KH
2018-04-27 14:52     ` Masami Hiramatsu
2018-04-27  7:04   ` Ingo Molnar
2018-04-27 15:58     ` Masami Hiramatsu
2018-04-27  6:40 ` [PATCH v3 2/7] kprobes: Show blacklist addresses as same as kallsyms does Masami Hiramatsu
2018-04-27  7:14   ` Ingo Molnar [this message]
2018-04-27 16:10     ` Masami Hiramatsu
2018-04-27  6:41 ` [PATCH v3 3/7] kprobes: Show address of kprobes if " Masami Hiramatsu
2018-04-27  6:41 ` [PATCH v3 4/7] kprobes: Replace %p with other pointer types Masami Hiramatsu
2018-04-27  6:56   ` Ingo Molnar
2018-04-27 15:42     ` Masami Hiramatsu
2018-04-28  4:43       ` Masami Hiramatsu
2018-04-27  6:42 ` [PATCH v3 5/7] kprobes/x86: Fix %p uses in error messages Masami Hiramatsu
2018-04-27  6:58   ` Ingo Molnar
2018-04-27 15:06     ` Masami Hiramatsu
2018-04-27  6:42 ` [PATCH v3 6/7] kprobes/arm: " Masami Hiramatsu
2018-04-27  6:43 ` [PATCH v3 7/7] kprobes/arm64: " Masami Hiramatsu

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