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Message-Id: <DBVFT81UT8ZU.1QI0T263LML5J@posteo.net>
Date: Wed, 06 Aug 2025 15:07:38 +0000
From: "Sertonix" <sertonix@...teo.net>
To: <musl@...ts.openwall.com>
Subject: ctr registry after syscall on powerpc
(Sorry for the noise, I don't know any better place to ask)
With GCC 15 I get a compiled musl libc that stores a value in the ctr
registry, doing a syscall which changes the ctr registry and then
reading back garbage data when trying to read the original value. I
unfortunatly couldn't find any information do determine if this is an
issue in musl, gcc or the kernel.
The relevant code from src/malloc/mallocng/malloc.c:
size_t pagesize = PGSZ; // stored into ctr registry
...
ctx.brk = brk(0); // mess up ctr registry
...
ctx.brk += -ctx.brk & (pagesize-1); // try to read back ctr registry
When I mark ctr as clobber in __syscall1 I don't see this issue. Is
that a correct fix?
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