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Date: Thu, 15 Mar 2018 09:37:28 -0400
From: Ryan Wilson-Perkin <>
Subject: Musl incompatibility with Docker and AWS's C5 class

Hey musl-devs,

Yesterday we tested out the new C5 instance class that AWS offers using our
Alpine-based images and discovered that we would get a segfault whenever we
ran `npm install`. Tracing the code, it appeared to be happening due to the
use of node's "process.setuid" and "process.setgid" commands, either of
which would cause a segfault.

We're running Alpine containers inside Docker on EC2, and the smallest
thing I can provide to reproduce this issue would be to run the following
on a C5 EC2 instance:

docker run -it node:9-alpine sh -c "node -e 'process.setgid(0)'"

A core dump provided the following limited information:

Program terminated with signal SIGSEGV, Segmentation fault.
warning: Unexpected size of section `.reg-xstate/26' in core file.
#0 __cp_end () at src/thread/x86_64/syscall_cp.s:29
29 src/thread/x86_64/syscall_cp.s: No such file or directory.
[Current thread is 1 (LWP 26)]
(gdb) bt
#0 __cp_end () at src/thread/x86_64/syscall_cp.s:29
#1 0x00007fd6161eecd8 in __syscall_cp_c (nr=202, u=<optimized out>,
v=<optimized out>, w=<optimized out>, x=<optimized out>, y=<optimized out>,
z=0) at src/thread/pthread_cancel.c:35
#2 0x00007fd6161ee2f5 in __timedwait_cp (addr=addr@...ry=0x5612e9ebf820,
val=val@...ry=-1, clk=clk@...ry=0, at=at@...ry=0x0,
priv=<optimized out>) at src/thread/__timedwait.c:31
#3 0x00007fd6161f0e2c in sem_timedwait (sem=0x5612e9ebf820, at=0x0) at
#4 0x00007fd615d7a5a4 in uv_sem_wait () from /usr/lib/
#5 0x00005612e94dc00c in node::DebugSignalThreadMain(void*) ()
#6 0x00007fd6161ef665 in start (p=0x7fd616424ab0) at
#7 0x00007fd6161f13e4 in __clone () at src/thread/x86_64/clone.s:21
Backtrace stopped: frame did not save the PC
*RYAN **WILSON-PERKIN* | Software Engineer
<> <>

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