From: Gary Guo <gary@xxxxxxxxxxx>
commit 75c1fd41a671a0843b89d1526411a837a7163fa2 upstream.
Without `-fno-builtin`, for functions like memcpy/memmove (and many
others), bindgen seems to be using the clang-provided prototype. This
prototype is ABI-wise compatible, but the issue is that it does not have
the same information as the source code w.r.t. typedefs.
For example, bindgen generates the following:
extern "C" {
pub fn strlen(s: *const core::ffi::c_char) -> core::ffi::c_ulong;
}
note that the return type is `c_ulong` (i.e. unsigned long), despite the
size_t-is-usize behavior (this is default, and we have not opted out
from it using --no-size_t-is-usize).
Similarly, memchr's size argument should be of type `__kernel_size_t`,
but bindgen generates `c_ulong` directly.
We want to ensure any `size_t` is translated to Rust `usize` so that we
can avoid having them be different type on 32-bit and 64-bit
architectures, and hence would require a lot of excessive type casts
when calling FFI functions.
I found that this bindgen behavior (which probably is caused by
libclang) can be disabled by `-fno-builtin`. Using the flag for compiled
code can result in less optimisation because compiler cannot assume
about their properties anymore, but this should not affect bindgen.
[ Trevor asked: "I wonder how reliable this behavior is. Maybe bindgen
could do a better job controlling this, is there an open issue?".
Gary replied: ..."apparently this is indeed the suggested approach in
https://github.com/rust-lang/rust-bindgen/issues/1770";. - Miguel ]
Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240913213041.395655-2-gary@xxxxxxxxxxx
[ Formatted comment. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
rust/Makefile | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -264,7 +264,11 @@ else
bindgen_c_flags_lto = $(bindgen_c_flags)
endif
-bindgen_c_flags_final = $(bindgen_c_flags_lto) -D__BINDGEN__
+# `-fno-builtin` is passed to avoid `bindgen` from using `clang` builtin
+# prototypes for functions like `memcpy` -- if this flag is not passed,
+# `bindgen`-generated prototypes use `c_ulong` or `c_uint` depending on
+# architecture instead of generating `usize`.
+bindgen_c_flags_final = $(bindgen_c_flags_lto) -fno-builtin -D__BINDGEN__
# Each `bindgen` release may upgrade the list of Rust target versions. By
# default, the highest stable release in their list is used. Thus we need to set
Patches currently in stable-queue which might be from ojeda@xxxxxxxxxx are
queue-6.12/drm-panic-avoid-reimplementing-iterator-find.patch
queue-6.12/documentation-rust-add-coding-guidelines-on-lints.patch
queue-6.12/rust-provide-proper-code-documentation-titles.patch
queue-6.12/rust-alloc-make-allocator-module-public.patch
queue-6.12/rust-alloc-remove-vecext-extension.patch
queue-6.12/rust-alloc-implement-reallocfunc.patch
queue-6.12/rust-alloc-separate-aligned_size-from-krealloc_aligned.patch
queue-6.12/rust-enable-clippy-unnecessary_safety_comment-lint.patch
queue-6.12/rust-alloc-update-module-comment-of-alloc.rs.patch
queue-6.12/rust-kbuild-expand-rusttest-target-for-macros.patch
queue-6.12/rust-error-use-core-alloc-layouterror.patch
queue-6.12/rust-str-test-replace-alloc-format.patch
queue-6.12/loongarch-use-asm_reachable.patch
queue-6.12/rust-alloc-implement-allocator-for-kmalloc.patch
queue-6.12/rust-alloc-implement-collect-for-intoiter.patch
queue-6.12/rust-alloc-introduce-arraylayout.patch
queue-6.12/rust-alloc-implement-vmalloc-allocator.patch
queue-6.12/documentation-rust-discuss-in-the-guidelines.patch
queue-6.12/rust-error-check-for-config-test-in-error-name.patch
queue-6.12/rust-enable-clippy-ignored_unit_patterns-lint.patch
queue-6.12/rust-enable-clippy-unnecessary_safety_doc-lint.patch
queue-6.12/rust-alloc-add-box-to-prelude.patch
queue-6.12/kbuild-rust-remove-the-alloc-crate-and-globalalloc.patch
queue-6.12/rust-alloc-add-allocator-trait.patch
queue-6.12/rust-treewide-switch-to-our-kernel-box-type.patch
queue-6.12/rust-introduce-.clippy.toml.patch
queue-6.12/rust-alloc-rename-kernelallocator-to-kmalloc.patch
queue-6.12/rust-alloc-implement-cmalloc-in-module-allocator_test.patch
queue-6.12/drm-panic-allow-verbose-version-check.patch
queue-6.12/rust-map-__kernel_size_t-and-friends-also-to-usize-isize.patch
queue-6.12/rust-alloc-add-module-allocator_test.patch
queue-6.12/rust-replace-clippy-dbg_macro-with-disallowed_macros.patch
queue-6.12/rust-alloc-add-__gfp_nowarn-to-flags.patch
queue-6.12/rust-enable-clippy-s-check-private-items.patch
queue-6.12/rust-error-make-conversion-functions-public.patch
queue-6.12/rust-sort-global-rust-flags.patch
queue-6.12/rust-alloc-implement-contains-for-flags.patch
queue-6.12/rust-init-remove-unneeded.patch
queue-6.12/rust-use-custom-ffi-integer-types.patch
queue-6.12/rust-sync-remove-unneeded.patch
queue-6.12/rust-treewide-switch-to-the-kernel-vec-type.patch
queue-6.12/rust-alloc-implement-kvmalloc-allocator.patch
queue-6.12/drm-panic-correctly-indent-continuation-of-line-in-list-item.patch
queue-6.12/rust-alloc-implement-kernel-vec-type.patch
queue-6.12/rust-workqueue-remove-unneeded.patch
queue-6.12/rust-error-optimize-error-type-to-use-nonzero.patch
queue-6.12/drm-panic-remove-unnecessary-borrow-in-alignment_pattern.patch
queue-6.12/rust-alloc-remove-extension-of-std-s-box.patch
queue-6.12/rust-block-fix-formatting-in-gendisk-doc.patch
queue-6.12/rust-enable-rustdoc-unescaped_backticks-lint.patch
queue-6.12/rust-fix-size_t-in-bindgen-prototypes-of-c-builtins.patch
queue-6.12/rust-enable-clippy-undocumented_unsafe_blocks-lint.patch
queue-6.12/rust-alloc-add-vec-to-prelude.patch
queue-6.12/rust-alloc-implement-intoiterator-for-vec.patch
queue-6.12/rust-alloc-implement-kernel-box.patch
queue-6.12/drm-panic-remove-redundant-field-when-assigning-value.patch
queue-6.12/rust-types-avoid-repetition-in-as-from-bytes-impls.patch
queue-6.12/rust-start-using-the-attribute.patch
queue-6.12/drm-panic-allow-verbose-boolean-for-clarity.patch
queue-6.12/maintainers-add-entry-for-the-rust-alloc-module.patch
queue-6.12/rust-alloc-fix-arraylayout-allocations.patch
queue-6.12/drm-panic-prefer-eliding-lifetimes.patch
