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SubjectRe: Sparc-32 doesn't work in 3.1.
[ CCed Jakub ]

>>> Boot time fixup v1.6. 4/Mar/98 Jakub Jelinek (jj@ultra.linux.cz).
>>> Patching kernel for srmmu[Fujitsu TurboSparc]/iommu
>>> Fixup i f029ddfc doesn't refer to a valid instruction at
>>> f00de648[95eea000]
>>> halt, power off

> I put the broken image up at http://landley.net/sparc-image for the
> moment, but if you build 3.1 with the attached .config and the toolchain
> mentioned last time, it should reproduce for you. It's 100% reliable
> for me...

Nice! With this config it breaks for me on your and mine toolchains.
The offending function is ext4_kvmalloc (and similar ext4_kvzalloc).

The usual relocation in sparc looks like a pair of instructions loading
two pats of address in 2 instructions:

Like that:
> sethi %hi(ext4_fill_super), %o4 !, tmp113
> or %o4, %lo(ext4_fill_super), %o4 ! tmp113,, tmp28

In our case relocatable symbol sits in tail call, so %lo part is in "unusual"
RESTORE instruction:

> ext4_kvmalloc:
...
> sethi %hi(___i_page_kernel), %i2 !, tmp112
> call __vmalloc, 0 !
> restore %i2, %lo(___i_page_kernel), %o2 ! tmp112,,
...

David: is this code correct? Or it's a compiler bug? I am sparc32 newbie.
(C source and asm sources of function are in [1])

I think this kind of code is generated only in -Os.
So to workaround it I tried this hack:

> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> ret = kmalloc(size, flags);
> if (!ret)
> ret = __vmalloc(size, flags, PAGE_KERNEL);
> +
> + asm __volatile__("nop":::"memory");
> +
> return ret;
> }
(for both ext4_kvmalloc / ext4_kvzalloc. Attached workaround as a patch.)

It forces compiler to geterate "usual" pattern for relocation.

I think of 2 solutions:

1. trying to fix sparc/boot/btfixupprep.c and arch/sparc/mm/btfixup.c
to distinct HI22 and LO10 relocations as different ones.
Right now they are merged into one 'i' type and rely on instruction heuristics to fix it.
2. Add a hack to arch/sparc/mm/btfixup.c to recognize restore instruction as well

Any others?

Hope that helps.

[1]:

void *ext4_kvmalloc(size_t size, gfp_t flags)
{
void *ret;

ret = kmalloc(size, flags);
if (!ret)
ret = __vmalloc(size, flags, PAGE_KERNEL);
return ret;
}

.global ext4_kvmalloc
.type ext4_kvmalloc, #function
.proc 0120
ext4_kvmalloc:
save %sp, -96, %sp !
mov %i0, %o0 ! size,
call __kmalloc, 0 !,
mov %i1, %o1 ! flags,
cmp %o0, 0 ! ret,
bne .LL274 !
sethi %hi(___i_page_kernel), %i2 !, tmp112
call __vmalloc, 0 !
restore %i2, %lo(___i_page_kernel), %o2 ! tmp112,,
.LL274:
jmp %i7+8
restore %g0, %o0, %o0 ! ret,
.size ext4_kvmalloc, .-ext4_kvmalloc

--

Sergei
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 44d0c8d..570d45e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -117,6 +117,7 @@ void *ext4_kvmalloc(size_t size, gfp_t flags)
ret = kmalloc(size, flags);
if (!ret)
ret = __vmalloc(size, flags, PAGE_KERNEL);
+ mb(); /* hack to pessimize code */
return ret;
}

@@ -127,6 +128,7 @@ void *ext4_kvzalloc(size_t size, gfp_t flags)
ret = kzalloc(size, flags);
if (!ret)
ret = __vmalloc(size, flags | __GFP_ZERO, PAGE_KERNEL);
+ mb(); /* hack to pessimize code */
return ret;
}
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