Nikodemus Siivola a écrit : > On 3/5/08, Debian Bug Tracking System <[EMAIL PROTECTED]> wrote: > >> tag 469058 + patch >> Bug#469058: sbcl doesn't reset direction flag upon exit >> There were no tags set. >> Tags added: patch > > Thanks for the patch, but... while I agree that it is good to change > SBCL to reset the direction flag every time it is diddled, instead of > just before calling C, I don't think SBCL is actually at fault here. > > 1. SBCL does actually reset DF before any call to foreign (GCC generated) > code. > See line 236 in src/compiler/x86/c-call.lisp, and line 125 in > src/runtime/x86-assem.S. > > (It is possible I'm missing out a call-path here, but even so, read on and > see if my fears are unfounded or not.) > > 2. If the problem was due to a foreign call, it should be deterministic. > > 3. If the problem was due to _returning_ to main(), it should be > deterministic.
Looks correct. > What I suspect is actually going on (especially considering your > statement that compiling signals/ with 4.2 avoided the issue) is that > a signal handler is entered while DF is set. What I am sure is that sigemptyset() from the glibc is called with the direction flag set, and that should not happen. > If this is the case, then clearing it right after each REP loop where > SBCL uses it just makes seeing the bug much more unlikely -- but not > impossible in the presence of async signals. Seems correct, though I have made half a dozen of build here, without any problem. > If so, this may also explain some _very_ hard to reproduce faults we > have seen over the years: using a pre 4.3-GCC compiled libc, a signal > at an in opportune moment in the middle of a REP loop could clear DF! > Yikes! > > I'm not sure what is The Right Thing here, though. Should SBCL (and > _any_ program that ever sets DF!) save, clear, and restore DF in its > signal handlers? Should libc/kernel do that? Should signals be blocked I currently have no idea about that. > before ever setting DF? Is setting DF Just A Bad Idea? I don't think so. Not setting DF means less optimized code has to be used. -- .''`. Aurelien Jarno | GPG: 1024D/F1BCDB73 : :' : Debian developer | Electrical Engineer `. `' [EMAIL PROTECTED] | [EMAIL PROTECTED] `- people.debian.org/~aurel32 | www.aurel32.net -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
