Date: Sun, 4 Dec 2016 00:04:12 +0000 From: Colin Percival <cperciva@tarsnap.com> To: freebsd-current@freebsd.org Subject: clang/llvm 3.9.0 mysteriously zeroing variables? Message-ID: <01000158c7252f0c-6c3198b0-fbef-4a60-ade9-e3b91d9e83bd-000000@email.amazonses.com>
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Starting with r309124 (when clang/llvm 3.9.0 was imported) I'm seeing EC2
instances panic on boot with a division-by-zero error; the code in question
is in blkfront.c, printing out the size of disks:
> device_printf(dev, "%juMB <%s> at %s",
> (uintmax_t) sectors / (1048576 / sector_size),
> device_get_desc(dev),
> xenbus_get_node(dev));
My first thought was that 'sector_size' must be either zero or very large...
but no, when I add printf("sector_size = %ju\n", (uintmax_t)sector_size), it's
entirely normal. What's more, adding that printf makes the division-by-zero
panic go away.
I'd think I was just hallucinating, but earlier today I heard that a similarly
"impossible" panic had been observed in the NFS client code when compiled with
clang/llvm 3.9.0.
So... is anyone else seeing unexpected panics or other odd behaviour starting
after clang/llvm 3.9.0 was imported?
--
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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