From: Alice Ryhl Date: Thu, 7 May 2026 11:14:42 +0000 (+0000) Subject: rust: kasan/kbuild: fix rustc-option when cross-compiling X-Git-Tag: v7.1-rc7~9^2~3 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=4a44b17406cb5a93f90af3df9392b3a45eb336fb;p=thirdparty%2Fkernel%2Flinux.git rust: kasan/kbuild: fix rustc-option when cross-compiling The Makefile version of rustc-option currently checks whether the option exists for the host target instead of the target actually being compiled for. It was done this way in commit 46e24a545cdb ("rust: kasan/kbuild: fix missing flags on first build") to avoid a circular dependency on target.json. However, because of this, rustc-option currently does not function when cross-compiling from x86_64 to aarch64 if CONFIG_SHADOW_CALL_STACK is enabled. This is because KBUILD_RUSTFLAGS contains -Zfixed-x18 under this configuration. Since that flag does not exist on the host target, rustc-option runs into a compilation failure every time, leading to all flags being rejected as unsupported. To fix this, update rustc-option to pass a --target parameter so that the host target is not used. For targets using target.json, use a built-in target that is as close as possible to the target created with target.json to avoid the circular dependency on target.json. One scenario where this causes a boot failure: * Cross-compiled from x86_64 to aarch64. * With CONFIG_SHADOW_CALL_STACK=y * With CONFIG_KASAN_SW_TAGS=y * With CONFIG_KASAN_INLINE=n Then the resulting kernel image will fail to boot when it first calls into Rust code with a crash along the lines of "Unable to handle kernel paging request at virtual address 0ffffffc08541796". This is because the call threshold is not specified, so rustc will inline kasan operations, but the kasan shadow offset is not specified, which leads to the inlined kasan instructions being incorrect. Note that the -Zsanitizer=kernel-hwaddress parameter itself does not lead to a rustc-option failure despite being aarch64-specific because RUSTFLAGS_KASAN has not yet been added to KBUILD_RUSTFLAGS when rustc-option is evaluated by the kasan Makefile. Cc: stable@vger.kernel.org Fixes: 46e24a545cdb ("rust: kasan/kbuild: fix missing flags on first build") Signed-off-by: Alice Ryhl Link: https://patch.msgid.link/20260507-rustc-option-cross-v2-1-2f650a49c2b5@google.com [ Edited slightly: - Reset variable to avoid using the environment. - Use a simply expanded variable flavor for simplicity. - Export variable so that behavior in sub-`make`s is consistent. This matches other variables. - Miguel ] Signed-off-by: Miguel Ojeda --- diff --git a/Makefile b/Makefile index b7b80e84e1eb2..1f205a0044372 100644 --- a/Makefile +++ b/Makefile @@ -607,6 +607,7 @@ KBUILD_RUSTFLAGS := $(rust_common_flags) \ -Crelocation-model=static \ -Zfunction-sections=n \ -Wclippy::float_arithmetic +KBUILD_RUSTFLAGS_OPTION_CHKS := KBUILD_AFLAGS_KERNEL := KBUILD_CFLAGS_KERNEL := @@ -643,7 +644,7 @@ export KBUILD_USERCFLAGS KBUILD_USERLDFLAGS export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE -export KBUILD_RUSTFLAGS RUSTFLAGS_KERNEL RUSTFLAGS_MODULE +export KBUILD_RUSTFLAGS RUSTFLAGS_KERNEL RUSTFLAGS_MODULE KBUILD_RUSTFLAGS_OPTION_CHKS export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_RUSTFLAGS_MODULE KBUILD_LDFLAGS_MODULE export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL KBUILD_RUSTFLAGS_KERNEL diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 46fec0b08487a..1d526a5d2a831 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -77,6 +77,10 @@ KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -mno-sse4a KBUILD_RUSTFLAGS += --target=$(objtree)/scripts/target.json KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2 +# The target.json file is not available when invoking rustc-option, so use the +# built-in target when checking whether flags are supported instead. +KBUILD_RUSTFLAGS_OPTION_CHKS += --target=x86_64-unknown-none + # # CFLAGS for compiling floating point code inside the kernel. # diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um index 19c13afa474e9..9adecd65639f3 100644 --- a/arch/x86/Makefile.um +++ b/arch/x86/Makefile.um @@ -14,6 +14,14 @@ endif KBUILD_RUSTFLAGS += --target=$(objtree)/scripts/target.json +# The target.json file is not available when invoking rustc-option, so use the +# built-in target when checking whether flags are supported instead. +ifeq ($(CONFIG_X86_32),y) +KBUILD_RUSTFLAGS_OPTION_CHKS += --target=i686-unknown-linux-gnu +else +KBUILD_RUSTFLAGS_OPTION_CHKS += --target=x86_64-unknown-linux-gnu +endif + ifeq ($(CONFIG_X86_32),y) START := 0x8048000 diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler index ef91910de265d..06bbe29c846ce 100644 --- a/scripts/Makefile.compiler +++ b/scripts/Makefile.compiler @@ -80,7 +80,7 @@ ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3)) # TODO: remove RUSTC_BOOTSTRAP=1 when we raise the minimum GNU Make version to 4.4 __rustc-option = $(call try-run,\ echo '$(pound)![allow(missing_docs)]$(pound)![feature(no_core)]$(pound)![no_core]' | RUSTC_BOOTSTRAP=1\ - $(1) --sysroot=/dev/null $(filter-out --sysroot=/dev/null --target=%,$(2)) $(3)\ + $(1) --sysroot=/dev/null $(KBUILD_RUSTFLAGS_OPTION_CHKS) $(filter-out --sysroot=/dev/null --target=%target.json,$(2)) $(3)\ --crate-type=rlib --out-dir=$(TMPOUT) --emit=obj=- - >/dev/null,$(3),$(4)) # rustc-option