SBCL uses Launchpad to track bugs. The bug database is available at:

  https://bugs.launchpad.net/sbcl

Reporting bugs there requires registering at Launchpad. However, bugs
can also be reported on the mailing list sbcl-bugs, which is
moderated but does _not_ require subscribing. Simply send email to

  sbcl-bugs@lists.sourceforge.net

and the bug will be checked and added to Launchpad by SBCL maintainers.

Historical note: before Launchpad was adopted this file contained a
list of currently open bugs. If you run into an SBCL bug number in the
range 1-431 inclusive, it refers to that list.

Refer to User Manual for more details.