Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
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Date: Fri, 26 Oct 2012 10:47:57 +0800
From: Brian Wang <>
Subject: Re: Difference between -O2 and -g

On Fri, Oct 26, 2012 at 10:32 AM, Rich Felker <> wrote:
> On Fri, Oct 26, 2012 at 10:04:46AM +0800, Brian Wang wrote:
>> > One very simple way to get a picture of what's going on in a program
>> > is to run it under strace. Try saving strace logs for both the working
>> > version and the broken version and comparing them either manually or
>> > with the diff utility (although the latter may be difficult unless you
>> > filter out the addresses and other contnets that will naturally
>> > differ, so it might be easier to visually inspect). If you don't
>> > already have an strace built for your target, I think Aboriginal Linux
>> > has static binaries you can use.
>> I have previously built my static strace.
>> I could not decipher what went wrong.  Please find the strace logs for
>> the three binaries in question.
>> The source code is basically the same, except for the musl ones,
>> printf calls are sprinkled here and there
>> as my desperate attempt.
> The good and bad traces diverge at this line, which only happens in
> the good one:
> writev(2, [{"CreateColormap : good end\n", 26}, {NULL, 0}], 2) = 26
> So search the source for that string and see what condition is causing
> that code to be reached or not reached.

Thank you for reading through them. :-)

The failed call (XaceHook) is:
     * Security creation/labeling check
    i = XaceHook(XACE_RESOURCE_ACCESS, clients[client], mid, RT_COLORMAP,
		 pmap, RT_NONE, NULL, DixCreateAccess);
    if (i != Success) {
	fprintf(stderr, "%s : 9\n", __func__);
	FreeResource(mid, RT_NONE);
	return i;
I got tired of lots of printfs.  That is why I would like the help of
However, with -O2 turned on, it is rather difficult to step through the code,
and without -O2, it will not go into the error path...

Are there any known alignment tricks that I should apply for ARM targets?




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