On Sat, Jun 28, 2025 at 8:30 PM H.J. Lu <[email protected]> wrote:
>
> Update functions with no_callee_saved_registers/preserve_none attribute
> to preserve frame pointer since caller may use it to save the current
> stack:
>
> pushq %rbp
> movq %rsp, %rbp
> ...
> call function
> ...
> leave
> ret
>
> If callee changes frame pointer without restoring it, caller will fail
> to restore its stack after callee returns.
Do we know why the caller failed to restore rbp? Are there any
assumptions in the middle-end that frame pointers must be callee saved
registers(even if it's marked as caller-saved)?
>
/* The current function is a function specified with the
"no_callee_saved_registers" attribute. */
TYPE_NO_CALLEE_SAVED_REGISTERS,
- /* The current function is a function specified with the "noreturn"
- attribute. */
- TYPE_NO_CALLEE_SAVED_REGISTERS_EXCEPT_BP,
Comments of "noreturn" part should be merged into that of
TYPE_NO_CALLEE_SAVED_REGISTERS.
+callee-saved registers. That is, all registers, except for stack and
+frame pointers, can be used as scratch registers. For example, this
The patch only excludes frame pointers but the document mentions both
stack and frame pointers?
--
BR,
Hongtao
