Messages in this thread | | | From | Guenter Roeck <> | Subject | Re: [PATCH 3/4] parisc: Use absolute_pointer for memcmp on fixed memory location | Date | Sun, 12 Sep 2021 13:28:32 -0700 |
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On 9/12/21 12:58 PM, Helge Deller wrote: > * Linus Torvalds <torvalds@linux-foundation.org>: >> On Sun, Sep 12, 2021 at 9:02 AM Guenter Roeck <linux@roeck-us.net> wrote: >>> >>> - running_on_qemu = (memcmp(&PAGE0->pad0, "SeaBIOS", 8) == 0); >>> + running_on_qemu = (memcmp(absolute_pointer(&PAGE0->pad0), "SeaBIOS", 8) == 0); >> >> This seems entirely the wrong thing to do, and makes no sense. That >> "&PAGE0->pad0" is a perfectly valid pointer, and that's not where the >> problem is. >> >> The problem is "PAGE0" itself: >> >> #define PAGE0 ((struct zeropage *)__PAGE_OFFSET) >> >> which takes that absolute offset and creates a pointer out of it. >> >> IOW, _that_ is what should have the "absolute_pointer()" thing, and in >> that context the name of that macro and its use actually makes sense. >> >> No? >> >> An alternative - and possibly cleaner - approach that doesn't need >> absolute_pointer() at all might be to just do >> >> extern struct zeropage PAGE0; >> >> and then make that PAGE0 be defined to __PAGE_OFFSET in the parisc >> vmlinux.lds.S file. >> >> Then doing things like >> >> running_on_qemu = !memcmp(&PAGE0.pad0, "SeaBIOS", 8); >> >> would JustWork(tm). > > Yes, this second approach seems to work nicely, although the patch > then gets slightly bigger. > Below is a tested patch. > I'll check it some further and apply it to the parisc tree then. >
There are several PAGE0-> references left in the code after applying your patch.
$ git grep "PAGE0->" arch/parisc/kernel/firmware.c: if (!PAGE0->mem_kbd.iodc_io) arch/parisc/kernel/firmware.c: real32_call(PAGE0->mem_kbd.iodc_io, arch/parisc/kernel/firmware.c: (unsigned long)PAGE0->mem_kbd.hpa, ENTRY_IO_CIN, arch/parisc/kernel/firmware.c: PAGE0->mem_kbd.spa, __pa(PAGE0->mem_kbd.dp.layers), arch/parisc/kernel/smp.c: WARN_ON(((unsigned long)(PAGE0->mem_pdc_hi) << 32 arch/parisc/kernel/smp.c: | PAGE0->mem_pdc) != pdce_proc);
After fixing those, I can build a parisc image and boot it in qemu (32 bit).
Guenter
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