Messages in this thread | | | Date | Thu, 20 Jan 2022 13:13:47 -0800 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 2/3] x86/boot: Allow to hook up alternative port I/O helpers |
| |
On Thu, Jan 20, 2022 at 07:38:26PM +0300, Kirill A. Shutemov wrote: > On Thu, Jan 20, 2022 at 05:15:43AM +0300, Kirill A. Shutemov wrote: > > diff --git a/arch/x86/boot/io.h b/arch/x86/boot/io.h > > new file mode 100644 > > index 000000000000..640daa3925fb > > --- /dev/null > > +++ b/arch/x86/boot/io.h > > @@ -0,0 +1,30 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +#ifndef BOOT_IO_H > > +#define BOOT_IO_H > > + > > +#include <asm/shared/io.h> > > + > > +struct port_io_ops { > > + unsigned char (*inb)(int port); > > + unsigned short (*inw)(int port); > > + unsigned int (*inl)(int port); > > + void (*outb)(unsigned char v, int port); > > + void (*outw)(unsigned short v, int port); > > + void (*outl)(unsigned int v, int port); > > +}; > > + > > +extern struct port_io_ops pio_ops; > > + > > +static inline void init_io_ops(void) > > +{ > > + pio_ops = (struct port_io_ops){ > > + .inb = inb, > > + .inw = inw, > > + .inl = inl, > > + .outb = outb, > > + .outw = outw, > > + .outl = outl, > > + }; > > +} > > + > > +#endif > > It works fine on x86-64, but breaks on i386: > > ld: Unexpected run-time relocations (.rel) detected! > > I'll change it to > > pio_ops.inb = inb; > pio_ops.inw = inw; > pio_ops.inl = inl; > pio_ops.outb = outb; > pio_ops.outw = outw; > pio_ops.outl = outl; > > It works, but I hate that I don't really have control here. I have no clue > why compiler generate different code after the change. It is very fragile. > > Do we really have no way to say compiler to avoid relactions here?
This one:
pio_ops = (struct port_io_ops){ .inb = inb, .inw = inw, .inl = inl, .outb = outb, .outw = outw, .outl = outl, };
.. actually allocates an anonymous struct in the .data section, which is memcpy'ed at runtime when the assignment occurs. That anonymous struct has .data -> .text relocations which have to be resolved at runtime because the distance between .data and .text isn't constant.
The working version:
pio_ops.inb = inb; pio_ops.inw = inw; pio_ops.inl = inl; pio_ops.outb = outb; pio_ops.outw = outw; pio_ops.outl = outl;
... only needs .text -> .text relocations which can be resolved at link time.
-- Josh
| |