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Subject: Re: Why uml-add-tls-support-debug-check-never-works is needed (was: Re: Fwd: Proposed additions to the ptrace(2) manpage, take 2) Date: Sunday 26 March 2006 19:43 From: Blaisorblade <[EMAIL PROTECTED]> To: Jeff Dike <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED] On Saturday 25 March 2006 02:17, Jeff Dike wrote: > On Sat, Mar 25, 2006 at 12:28:09AM +0100, Blaisorblade wrote: > > BUT, this context switch at the thread born is special: the thread being > > switched away switches to a new thread not in the body of the new > > thread's call to switch_to_skas->switch_threads(), but in the body of > > thread_wait()! At that point, we lose the call to arch_switch_to_skas()! > > Yuck yuck yuck. Nice spotting. > > There's an obvious one-line fix for this, but I wonder if we ought to > try some restructuring to avoid this sort of thing in the future. Code which two people aren't able to understand until two years later _wants_ at least some comments and if possible restructuring. The problem is how, and I'm not looking at the code right now. Off the top of my head, I get only silly ideas, since we can't join the end of switch_to_skas() and fork_handler(). > > Questions and notes: > > > > *) Why does arch/um/os-Linux/skas/process.c has still one siglongjmp() > > call and sigjmp_buf vars, and that has no comments? > > I'm tempted to say that I just missed the call somehow. I see no > reason for that to be different, especially since it's preceded by a > UML_SIGSETJMP. As for the sigjmp_buf variables, I don't get your > point. Those haven't changed. I didn't study softints, but setjmp() is supposed to use jmp_buf's, not sigjmp_buf's (I know they are (almost) equal in the glibc headers I've seen, but that equality is not guaranteed). The fact that the code compiles without warnings can be seen as a bug in glibc headers. > > *) Also, why thread_wait and thread_switch are almost identical, yet > > they're two different functions? > > switch_threads? In order to merge them, you'd have to pass in the 1 > and the INIT_JMP_REMOVE_SIGSTACK, which I have conceptual problems > with. First, that makes the callers know things that they probably > shouldn't. If you don't pass 1 and INIT_JMP_REMOVE_SIGSTACK but two further defines like "JUMP_TO_INITIAL_THREAD" and "JUMP_BACK" (or actually meaningful names) the caller won't know more than it knows now. Or you can keep the callers intact - just by making switch_threads() and thread_wait() two inline wrappers. > Second, the 1 and the INIT_JMP_REMOVE_SIGSTACK have > completely different meanings. One is a message to the initial thread > that it has to do something. The 1 is a message to setjmp that is has > been longjmp-ed to. -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ------------------------------------------------------- -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ User-mode-linux-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
