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Date: Tue, 19 Jan 2021 12:17:48 -0800
From: Rasmus Andersson <>
Subject: Re: waitpid (wait4) on Linux 5 returns invalid values

On Tue, Jan 19, 2021 at 11:33 AM Markus Wichmann <> wrote:
> On Tue, Jan 19, 2021 at 10:18:04AM -0800, Rasmus Andersson wrote:
> > However the wait4 syscall[3] in Linux 5 returns other values,
> > specifically it returns errors as negative values. The error that
> > trips up programs like runit's runsv is ECHILD (-10) which wait4
> > returns when there are no children (i.e. they have exited.)
> >
> Hmm... that is very weird. That should not happen. Because the
> syscall_cp macro already contains a call to __syscall_ret(), which does
> exactly what you propose. So that means, there is something else going
> on in your copy of the code. Did you change anything about the source
> code? Or can you disassemble the function to see what it does?
Strange! You are right of course; looking at src/internal/syscall.h I
indeed see that syscall_cp calls __syscall_ret(__syscall_cp(args))
The musl I'm building with comes from which
is created from these scripts according to the author: It doesn't seem to apply any patches.
Anyhow, I'm currently building musl & gcc myself using
musl-cross-make. I will see how that pans out and report back.
Thank you for your quick response Markus!

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