diff options
| author |   Nathan Chancellor <nathan@kernel.org> | 2026-09-25 22:46:32 +0100 |
|---|---|---|
| committer |   Jason A. Donenfeld <Jason@zx2c4.com> | 2026-10-02 12:12:13 +0200 |
| commit | eb13a1ff271b0d180687eebb30611b0b276d5193 (patch) | |
| tree | 03fd4fbd2665a1e8816353cf8e7f3bf7f5b6ce90 /init/Kconfig | |
| parent | random: fix vgetrandom_opaque_params kernel-doc (diff) | |
random: vDSO: avoid call to memset() when zeroing reserved parameterHEADrandom-7.3-rc6-for-linusmaster
After a recent change in LLVM [1], builds with the random vDSO
implementation, such as PowerPC and RISC-V, fail when checking the vDSO:
arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not supported
arch/riscv/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported
memset() is now generated when zeroing params->reserved for some builds
because LLVM has an optimization (now run in more instances) that can
recognize at compile time when it is assigning a static value to a
contiguous area of memory and turn that into a call to memset(). Both
clang and GCC assume memset() is always available [2].
Clang has an internal fiddly hook, -max-store-memset, which we can set
to a high number, to disable generating out of line memset calls [3].
Similarly, GCC has -finline-stringops=memset to do the same [4], should
this issue ever hit future version of GCC. While these options wouldn't
make sense for normal kernel code, it is fine for the extremely limited
and intentionally compact vDSO code.
Link: https://github.com/llvm/llvm-project/commit/90cebef1411617fc3eedd359bdf00cb44b1c2439 [1]
Link: https://gcc.gnu.org/onlinedocs/gcc-16.2.0/gcc/Standards.html#index-ffreestanding [2]
Link: https://github.com/llvm/llvm-project/commit/b28eeb28bea39148738dc375e8a97072a1907e64 [3]
Link: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-finline-stringops [4]
Closes: https://github.com/ClangBuiltLinux/linux/issues/2183
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Diffstat (limited to 'init/Kconfig')
| -rw-r--r-- | init/Kconfig | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig index 8583d9f06c52..ad592fdf29af 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -173,6 +173,11 @@ config CC_HAS_ALLOC_TOKEN config CC_HAS_MULTIDIMENSIONAL_NONSTRING def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror) +config CC_OPT_INLINE_MEMSET + string + default "-finline-stringops=memset" if $(cc-option,-finline-stringops=memset) + default "-mllvm -max-store-memset=4294967294" if $(cc-option,-mllvm -max-store-memset=4294967294) + config LD_CAN_USE_KEEP_IN_OVERLAY # ld.lld prior to 21.0.0 did not support KEEP within an overlay description # https://github.com/llvm/llvm-project/pull/130661 |