musl - Difference in pthread behavior between glibc and musl

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Message-ID: <D05988EE-5C2C-4893-ABA8-F35570CD83C7@amazon.com>
Date: Tue, 11 Jul 2023 19:19:50 +0000
From: "Appelmans, Madeleine" <madelea@...zon.com>
To: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
Subject: Difference in pthread behavior between glibc and musl

Hello,

There seems to be a difference in pthread behavior when compiling with glibc and using the musl-gcc wrapper. The attached snippet of code creates a destructor attribute which deletes a pthread key. The code never actually creates the pthread key. This code segfaults when compiled using musl-gcc, and does not segfault when compiled with gcc.

Best guess at what is going on: When creating a pthread key, musl initializes a field called tsd<https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_key_create.c#n37>. When deleting a key, musl assumes that initialization has been done, and dereferences tsd without checking that it exists: see here<https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_key_create.c#n65>. This dereference may be the source of the segfault.

Thanks,
Madeleine

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