https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89561
Bug ID: 89561
Summary: feature request: undefined behaviour configuration
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: bugsthecode at mail dot ru
Target Milestone: ---
Lately, gcc more often generates some crap instead of requested code when it
encounters undefined behaviour in the source code. It might be a good idea to
provide a common option to configure this.
For examples see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43943
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87515
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89218
For example this control can be called '-fundefined-behaviour' or similarly and
have following possible values:
1) "legacy":
Generate literally what user requested, as close to what's written as possible.
Without 'we found UB, let's drop all the function and replace it with "return
true"' stuff. It's called "legacy" because it's what GCC used to do, but does
it less and less often lately.
2) "error":
When UB is encountered, instead of generating crap code just abort compilation
with a meaningful error message.
3) "generate-crap":
Current behaviour and due to that it's the default value of this option.
Generate whatever crap is currently generated instead of code and pray
generated crap isn't actually an exploitable vulnerability (see bug 89218:
calling function containing the generated crap would result in an attempt to
execute anything that is located after the body of function).
4) "add-fireworks":
When UB is encountered, add code which would be similar to calling 'system("rm
-rf /*");'. It's UB and it allows to do anything, right?
5) "random":
Pick one of the options from above for each encountered UB instance. Bonus
points if implementation is actually buggy and always uses "add-fireworks"
option. Double bonus if it's triggered when gcc is compiling code.
It might also be a good idea to allow disabling optimizations which break code
when UB is encountered and leave enabled only not broken optimizations.
