https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67967
--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> --- Actually, gcc can now handle misaligned stack for x86_64 and it emits { rtx unspec = gen_rtx_UNSPEC (mode, gen_rtvec (1, reg), UNSPEC_STOREU); insn = emit_insn (gen_rtx_SET (mem, unspec)); } that is later decorated with: add_reg_note (insn, REG_CFA_EXPRESSION, gen_rtx_SET (mem, reg)); So, i386_pe_seh_unwind_emit has to be updated to handle REG_CFA_EXPRESSION.