From: fche@redhat.com (Frank Ch. Eigler)
To: Ian Lance Taylor <iant@google.com>
Cc: Janboe Ye <yuan-bo.ye@motorola.com>,
gcc@gcc.gnu.org, janboe.ye@gmail.com
Subject: Re: how to use expand_builtin_alloca
Date: Thu, 16 Jul 2009 22:32:00 -0000 [thread overview]
Message-ID: <y0mskgw1cpu.fsf@fche.csb> (raw)
In-Reply-To: <m37hycwads.fsf@google.com> (Ian Lance Taylor's message of "Mon, 13 Jul 2009 14:17:35 -0700")
> Janboe Ye <yuan-bo.ye@motorola.com> writes:
>> normally gcc will use expand_builtin_alloca to handle variable array.
>> But mudflap will force this function to return immediately to invoke
>> alloca explicit.
>>
>> Is there some way to still use expand_builtin_alloca without changing
>> gcc source code?
I don't think so.
Ian Lance Taylor <iant@google.com> writes:
> mudflap can't check accesses to memory allocated using alloca unless
> it overrides __builtin_alloca.
It can't currently. But instead of redirecting the call to a
heap-based alloca() wannabe in libmudflap/mf-hooks1.c, perhaps
mudflap could instrument alloca() by generating code like this
instead:
__builtin_alloca(N) --> GIMPLE_TRY_FINALLY( try {
ptr = __builtin_alloca(N)
__mf_register(ptr ...)
ptr;
} finally (attached to the function scope) {
__mf_unregister(ptr ...)
}
Or perhaps not, if alloca() can be used in loops in way that
prevents clean nesting of the try/finally.
OTOH, I believe the original poster's case came from gcc-synthesized
alloca's, coming from variable-length array allocation. Those in turn
might be represented with almost the normal mf_xform_decls(), while
letting __builtin_alloca() remain.
Either of these requires gcc changes though.
> [...] Although, of course, you could simply not use mudflap for the
> code in question.
The original poster's purpose is specifically to build bits of the
linux kernel with mudflap instrumentation.
- FChE
next prev parent reply other threads:[~2009-07-16 22:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-13 21:08 Janboe Ye
2009-07-13 21:17 ` Ian Lance Taylor
2009-07-13 21:27 ` Janboe Ye
2009-07-13 21:39 ` Ian Lance Taylor
2009-07-16 22:32 ` Frank Ch. Eigler [this message]
2009-07-19 20:08 ` ye janboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=y0mskgw1cpu.fsf@fche.csb \
--to=fche@redhat.com \
--cc=gcc@gcc.gnu.org \
--cc=iant@google.com \
--cc=janboe.ye@gmail.com \
--cc=yuan-bo.ye@motorola.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).