Date: Sat, 25 Feb 2012 08:32:13 -0500 From: Rich Felker <dalias@...ifal.cx> To: musl@...ts.openwall.com Subject: Re: tough choice on thread pointer initialization issue On Sat, Feb 25, 2012 at 01:56:13AM -0500, Rich Felker wrote: > I've looked into the "solution 4" that Solar proposed, which simply > put is making __pthread_self() check for a clobbered thread register > and restore it. While this sounds simple, there are a few issues I've > run into whereby it starts to get ugly... Some revisions... it's not quite as bad as I said, but still not good either.. > with, but from reading the kernel sources, it looks like %fs is 0 and > a hidden 64-bit offset is stored in a privileged register accessible > only by the kernel (one which hopefully would not be clobbered by > sigreturn, but I'm not sure...) when the thread pointer does not fit > in 32 bits, and the old i386 method (LDT entry and non-zero %fs > selector value) is used when the thread pointer fits in 32 bits. This Got the cases reversed I think, but the issue still stands. > pointer is valid, we can't restore it (and the value of %fs might > actually need to differ per-thread if some threads are below the 4gb > boundary and others are located above). Per-thread difference is irrelevant since only the main thread can ever experience this problem; all new threads start with a valid thread pointer. Rich
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.