Re: [PATCH] Reserve a slot for argv[0] in default_arg.

On 2009-10-04, Jeff King wrote:

On Sat, Oct 03, 2009 at 03:29:31PM +0200, Petter Urkedal wrote:

quoted

Setting "av" to one slot before the allocated "default_arg" array causes
glibc abort with "free(): invalid next size (normal)" in some
configurations (Gentoo, glibc-2.9_p20081201-r2, gcc-5.3.2 with PIE).

Thanks, your fix looks sane. But I am curious about whether we are
triggering some glibc pickiness that is in your setup, or if we are
somehow violating the assumption that we only ever look at
default_arg[1] and beyond.

I was wondering myself.  I tried to switch off optimisation, but that
had no effect.  I'm suspecting PIE, but it could be some other
configuration implied by the Gentoo "hardened" use-flag.

What show-branch command did you issue to hit this? I was hoping to run
it under valgrind.

I can reproduce it on my machine with

    mkdir test-repo; cd test-repo
    /path/to/git init
    /path/to/git config showbranch.default --topo-order
    /path/to/git show-branch

Also:

quoted

+			if (!default_num)
+			    /* One unused position for argv[0]. */
+			    default_arg[default_num++] = NULL;

I don't know if we have a style rule for comments on single line
conditionals, but I had to read this a few times to make sure it wasn't
missing braces.

Comment's are treated as whitespace, but I'll adjust it for readability.
Maybe worse: I missed the 8-column indentation.  So, here is the patch
again (attached, I hope Git can extract it).