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From: Jeff King <>
To: "René Scharfe" <>
Cc: Git Mailing List <>,
	Derrick Stolee <>,
	Junio C Hamano <>
Subject: Re: [PATCH] gc: fix cast in compare_tasks_by_selection()
Date: Tue, 17 Nov 2020 17:30:11 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Nov 17, 2020 at 10:59:49PM +0100, René Scharfe wrote:

> compare_tasks_by_selection() is used with QSORT and gets passed pointers
> to the elements of "static struct maintenance_task tasks[]".  It casts
> the *addresses* of these passed pointers to element pointers, though,
> and thus effectively compares some unrelated values from the stack.  Fix
> the casts to actually compare array elements.
> Detected by USan (make SANITIZE=undefined test).

I checked the caller here, and indeed, it's passing an array-of-struct
so your patch is doing the right thing (not that I doubted it, but
that's what review is for).

This qsort void-pointer convention seems to create a lot of confusion
(not just the lack of type-safety, but the fact that it's getting a
pointer to the element). I felt like we had a discussion about this a
while ago, and indeed, I found:

The whole sub-thread is worth reading, but the macro you arrived at in:

seems pretty reasonable.


      reply	other threads:[~2020-11-17 22:30 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-17 21:59 René Scharfe
2020-11-17 22:30 ` Jeff King [this message]

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