Date: Tue, 30 Mar 2021 15:31:03 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 254661] Debug registers seem to be inherited in forked processes Message-ID: <bug-254661-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254661 Bug ID: 254661 Summary: Debug registers seem to be inherited in forked processes Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: mgorny@gentoo.org CC: emaste@freebsd.org, kib@FreeBSD.org Created attachment 223712 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=223712&action=edit fbsd-fork-dbreg.c It seems that when a process forks, the new child process inherits debug registers from the parent. Not sure if this is desirable but it's certainly different than e.g. Linux and NetBSD do (both clear dbregs in the new process). This currently breaks e.g. GDB that doesn't account for this. If the process has any watchpoints set before forking, the watchpoints leak to child process when it's being detached, and it crashes with SIGTRAP afterwards. I'm attaching yet another variant of my cheap reproducer script™. It sets dbreg on the parent process before fork, and then reads dbreg from the child after fork. The results I get are: dr0 = 0x204690 // set in parent process dr7 = 00000013 dr0 = 0x204690 // read in child process dr7 = 00000413 -- You are receiving this mail because: You are the assignee for the bug.help
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