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6711f72301
commit 6a069876eb1402478900ee0eb7d7fe276bb1f4e3 upstream.
On 32-bit ARM, you may encounter linker errors such as this one:
ld.lld: error: undefined symbol: _find_next_zero_bit
>>> referenced by rust_binder_main.43196037ba7bcee1-cgu.0
>>> drivers/android/binder/rust_binder_main.o:(<rust_binder_main::process::Process>::insert_or_update_handle) in archive vmlinux.a
>>> referenced by rust_binder_main.43196037ba7bcee1-cgu.0
>>> drivers/android/binder/rust_binder_main.o:(<rust_binder_main::process::Process>::insert_or_update_handle) in archive vmlinux.a
This error occurs because even though the functions are declared by
include/linux/find.h, the definition is #ifdef'd out on 32-bit ARM. This
is because arch/arm/include/asm/bitops.h contains:
#define find_first_zero_bit(p,sz) _find_first_zero_bit_le(p,sz)
#define find_next_zero_bit(p,sz,off) _find_next_zero_bit_le(p,sz,off)
#define find_first_bit(p,sz) _find_first_bit_le(p,sz)
#define find_next_bit(p,sz,off) _find_next_bit_le(p,sz,off)
And the underscore-prefixed function is conditional on #ifndef of the
non-underscore-prefixed name, but the declaration in find.h is *not*
conditional on that #ifndef.
To fix the linker error, we ensure that the symbols in question exist
when compiling Rust code. We do this by defining them in rust/helpers/
whenever the normal definition is #ifndef'd out.
Note that these helpers are somewhat unusual in that they do not have
the rust_helper_ prefix that most helpers have. Adding the rust_helper_
prefix does not compile, as 'bindings::_find_next_zero_bit()' will
result in a call to a symbol called _find_next_zero_bit as defined by
include/linux/find.h rather than a symbol with the rust_helper_ prefix.
This is because when a symbol is present in both include/ and
rust/helpers/, the one from include/ wins under the assumption that the
current configuration is one where that helper is unnecessary. This
heuristic fails for _find_next_zero_bit() because the header file always
declares it even if the symbol does not exist.
The functions still use the __rust_helper annotation. This lets the
wrapper function be inlined into Rust code even if full kernel LTO is
not used once the patch series for that feature lands.
Yury: arches are free to implement they own find_bit() functions. Most
rely on generic implementation, but arm32 and m86k - not; so they require
custom handling. Alice confirmed it fixes the build for both.
Cc: stable@vger.kernel.org
Fixes:
|
||
|---|---|---|
| .. | ||
| atomic.c | ||
| auxiliary.c | ||
| barrier.c | ||
| binder.c | ||
| bitmap.c | ||
| bitops.c | ||
| blk.c | ||
| bug.c | ||
| build_assert.c | ||
| build_bug.c | ||
| clk.c | ||
| completion.c | ||
| cpu.c | ||
| cpufreq.c | ||
| cpumask.c | ||
| cred.c | ||
| device.c | ||
| dma.c | ||
| drm.c | ||
| err.c | ||
| fs.c | ||
| helpers.c | ||
| io.c | ||
| irq.c | ||
| jump_label.c | ||
| kunit.c | ||
| maple_tree.c | ||
| mm.c | ||
| mutex.c | ||
| of.c | ||
| page.c | ||
| pci.c | ||
| pid_namespace.c | ||
| platform.c | ||
| poll.c | ||
| processor.c | ||
| property.c | ||
| rbtree.c | ||
| rcu.c | ||
| refcount.c | ||
| regulator.c | ||
| scatterlist.c | ||
| security.c | ||
| signal.c | ||
| slab.c | ||
| spinlock.c | ||
| sync.c | ||
| task.c | ||
| time.c | ||
| uaccess.c | ||
| usb.c | ||
| vmalloc.c | ||
| wait.c | ||
| workqueue.c | ||
| xarray.c | ||