[PATCH v2] x86-64: Allocate state buffer space for RDI, RSI and RBX

[H.J. Lu]

On Sun, Mar 17, 2024 at 1:26 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > diff --git a/sysdeps/x86/sysdep.h b/sysdeps/x86/sysdep.h
> > index db8e576e91..262d4083e2 100644
> > --- a/sysdeps/x86/sysdep.h
> > +++ b/sysdeps/x86/sysdep.h
> > @@ -46,6 +46,13 @@
> >     red-zone into account.  */
> >  # define STATE_SAVE_OFFSET (8 * 7 + 8)
> >
> > +/* _dl_tlsdesc_dynamic preserves RDI, RSI and RBX before realigning
> > +   stack.  After realigning stack, it saves RCX, RDX, R8, R9, R10 and
> > +   R11.  Allocate space for all integer registers and round up the state
> > +   size to 64 bytes to avoid clobbering saved RDI, RSI and RBX values on
> > +   stack by xsave on STATE_SAVE_OFFSET(%rsp).  */
> > +# define TLSDESC_CALL_STATE_SAVE_OFFSET (STATE_SAVE_OFFSET + 64)
>
> Why 64?  The red zone is 128 bytes, and the three registers only need 24
> bytes.  I think 24 has to be rounded up to 64 to preserve the XSAVE area
> alignment.

I changed it to 24.

> The macro is also misnamed because it is not an offset.  The real offset
> depends on what the stack realignment did.
>

I renamed it to TLSDESC_CALL_REGISTER_SAVE_AREA in the v3 patch:

https://patchwork.sourceware.org/project/glibc/list/?series=31971

-- 
H.J.