Re: [PATCH gnumach] Align the user stack correctly for 64 bit programs.

[Luca]

Il 21/03/23 04:58, Flávio Cruz ha scritto:
>     Il 20/03/23 05:59, Flavio Cruz ha scritto:
>      > diff --git a/i386/i386/thread.h b/i386/i386/thread.h
>      > index cb317bee..c5da7522 100644
>      > --- a/i386/i386/thread.h
>      > +++ b/i386/i386/thread.h
>      > @@ -225,6 +225,17 @@ typedef struct pcb {
>      >   #define STACK_IEL(stack)    \
>      >       ((struct i386_exception_link *)STACK_IKS(stack) - 1)
>      >
>      > +#ifdef __x86_64__
>      > +#ifdef USER32
>      > +#define STACK_ALIGN 4
>      > +#else
>      > +/* Follow System V AMD64 ABI guidelines. */
>      > +#define STACK_ALIGN 16
>      > +#endif
>      > +#else
>      > +#define STACK_ALIGN 4
>      > +#endif  /* __x86_64__ */
>      > +
>      >   #define USER_REGS(thread)   (&(thread)->pcb->iss)
>
>     Maybe this should be BOOTSTRAP_STACK_ALIGN or something similar?
>     Just to
>     differentiate from the alignment set in pcb_module_init(), which is for
>     the exception stack.
>
>
> Is the exception stack only used in kernel space? In that case, we could 
> define
> KERNEL_STACK_ALIGN and USER_STACK_ALIGN to differentiate between the
> two cases. 64 bit user programs always need to have a 16-byte aligned 
> stack when
> calling functions (at least gcc expects that).

Yes, the exception stack is not visible from user space, and it must 
follow the kernel arch rather than the user arch.


Luca