On 7/14/2025 3:20 AM, Peter Zijlstra wrote:
call __fred_entry_from_kvm /* Call the C entry point */
- POP_REGS
- ERETS
-1:
+
+1: /*
The symbol "1" is misplaced; it needs to be put after the ERETS
instruction.
+ * When FRED, use ERETS to potentially clear NMIs, otherwise simply
+ * restore the stack pointer.
+ */
+ ALTERNATIVE "nop; nop; mov %rbp, %rsp", \
Why explicitly add two nops here?
ALTERNATIVE will still pad three-byte nop after the MOV instruction.
+ __stringify(add $C_PTREGS_SIZE, %rsp; ERETS), \
+ X86_FEATURE_FRED
+
/*
- * Objtool doesn't understand what ERETS does, this hint tells it that
- * yes, we'll reach here and with what stack state. A save/restore pair
- * isn't strictly needed, but it's the simplest form.
+ * Objtool doesn't understand ERETS, and the cfi register state is
+ * different from initial_func_cfi due to PUSH_REGS. Tell it the state
+ * is similar to where UNWIND_HINT_SAVE is.
*/
UNWIND_HINT_RESTORE
+
pop %rbp
RET
