On Mon, Jun 30, 2025 at 10:37 AM Hongtao Liu <crazy...@gmail.com> wrote: > > On Sat, Jun 28, 2025 at 8:30 PM H.J. Lu <hjl.to...@gmail.com> 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)?
Since RBP is changed by callee, "leave", which does mov %rbp, %rsp pop %rbp no longer works as RBP is wrong. > > > > /* 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. Will update. > +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? Stack pointer is implied. My patch makes it clear. > > > -- > BR, > Hongtao -- H.J.
