[Bug middle-end/85751] New: RFE: option to align code using breakpoint instructions when unreachable

[hpa at zytor dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85751

            Bug ID: 85751
           Summary: RFE: option to align code using breakpoint
                    instructions when unreachable
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hpa at zytor dot com
  Target Milestone: ---

For most (all?) targets, there exists a breakpoint or other trap instruction
which can be inserted at any point in the code stream, e.g. 0xcc (int3) on x86.

Currently, gcc aligns code by the default platform option, which is some kind
of NOP, as the assembler can't know if a fallthrough is possible.

It would be preferable to pad with a trapping instruction *if* the padding area
is unreachable and not subject to fallthrough.

This does not require any binutils changes, as the align directives already
optionally support specifying the value of the padding bytes.