On Sat, Sep 26, 2026 at 12:55:34PM +0200, Christophe Leroy (CS GROUP) wrote: > Hi Jason, > > Le 26/09/2026 à 12:02, Jason A. Donenfeld a écrit : > > On Fri, Sep 25, 2026 at 03:00:46PM -0700, Nick Desaulniers wrote: > >> On Fri, Sep 25, 2026 at 2:56 PM Nick Desaulniers > >> <[email protected]> wrote: > >>> > >>> On Fri, Sep 25, 2026 at 2:53 PM Nick Desaulniers > >>> <[email protected]> wrote: > >>>> > >>>> On Fri, Sep 25, 2026 at 2:46 PM Nathan Chancellor <[email protected]> > >>>> wrote: > >>>>> > >>>>> 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 provides a builtin, __builtin_memset_inline [3][4], that can be > >>>>> used to ensure an external function call is not generated when zeroing > >>>>> this memory. Use it when it is available. > >>>>> > >>>>> While GCC has no issues with the current code, it has generated memset() > >>>>> before, as seen in commit b7bad082e113 ("random: vDSO: avoid call to out > >>>>> of line memset()"). GCC 14 provides '-finline-stringops=memset' [5][6] > >>>>> with a similar guarantee to the clang builtin, so use it and > >>>>> __builtin_memset() when available. > >>>>> > >>>>> If no option is available, provide a simple memset_inline() like the one > >>>>> from lib/string.c to avoid adding an ugly ifdef. > >>>>> > >>>>> Link: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fcommit%2F90cebef1411617fc3eedd359bdf00cb44b1c2439&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659627802%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=ku4l8Ol5OJ2qi%2BcSblspxxUKOA6rNpiUO3ZvGSoAb1s%3D&reserved=0 > >>>>> [1] > >>>>> Link: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fonlinedocs%2Fgcc-16.2.0%2Fgcc%2FStandards.html%23index-ffreestanding&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659651194%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=jQa1eTDLk3cPNTa3GEBwVEohHh67ukShaRHMZvA%2FHDg%3D&reserved=0 > >>>>> [2] > >>>>> Link: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fcommit%2F38637ee477541370a90b37f149069d8e5c0c2efd&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659668579%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=zY7Kr9ZZNNZR%2FVsnwYRlubPRpbMaKe9QtMD2snd8ZvA%3D&reserved=0 > >>>>> [3] > >>>>> Link: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fclang.llvm.org%2Fdocs%2FLanguageExtensions.html%23guaranteed-inlined-memset&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659678360%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=vUU2fhCVcUWsbQD3IsRaUzSO8KVSpxwSpgr9San4aq0%3D&reserved=0 > >>>>> [4] > >>>>> Link: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fgit%2F%3Fp%3Dgcc.git%3Ba%3Dcommit%3Bh%3D1ff6d9f7428b0668cd8ab0b3e3ab94f1d733124d&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659687815%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=qHRqxAO252imwH1W93yHlp6jdcFGkFOr2Y2hXbG2MLU%3D&reserved=0 > >>>>> [5] > >>>>> Link: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fonlinedocs%2Fgcc%2FOptimize-Options.html%23index-finline-stringops&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659698298%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=0ecc%2BXd6o3nozh3N71aq%2F98Xam%2Fdol7GUHmC637Iv7I%3D&reserved=0 > >>>>> [6] > >>>>> Suggested-by: "Jason A. Donenfeld" <[email protected]> > >>>>> Suggested-by: Nick Desaulniers <[email protected]> > >>>>> Signed-off-by: Nathan Chancellor <[email protected]> > >>>>> --- > >>>>> Changes in v2: > >>>>> - Switch approach entirely (Jason, Nick) > >>>>> - clang: use __builtin_memset_inline() to avoid external call > >>>>> - GCC 14+: use __builtin_memset + -finline-stringops=memset (hence > >>>>> the > >>>>> massive CC list increase) > >>>>> - GCC < 14: no issues currently but avoid ifdef with simple memset > >>>>> implementation > >>>>> - Link to v1: > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatch.msgid.link%2F20260916-vdso-getrandom-avoid-memset-llvm-24-v1-1-80a92f2e225a%40kernel.org&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659712983%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=%2Ftq3tUHqDmbXesqB69w6umXAuaTsfzOIhk54Jy76cwo%3D&reserved=0 > >>>>> --- > >>>>> arch/arm64/kernel/vdso/Makefile | 2 +- > >>>>> arch/loongarch/vdso/Makefile | 1 + > >>>>> arch/powerpc/kernel/vdso/Makefile | 1 + > >>>>> arch/riscv/kernel/vdso/Makefile | 1 + > >>>>> arch/s390/kernel/vdso/Makefile | 1 + > >>>>> arch/x86/entry/vdso/vdso64/Makefile | 2 +- > >>>>> init/Kconfig | 7 +++++++ > >>>>> lib/vdso/getrandom.c | 19 +++++++++++++++++-- > >>>>> 8 files changed, 30 insertions(+), 4 deletions(-) > >>>>> > >>>>> diff --git a/arch/arm64/kernel/vdso/Makefile > >>>>> b/arch/arm64/kernel/vdso/Makefile > >>>>> index 7dec05dd33b7..f6619e1cb2ce 100644 > >>>>> --- a/arch/arm64/kernel/vdso/Makefile > >>>>> +++ b/arch/arm64/kernel/vdso/Makefile > >>>>> @@ -41,7 +41,7 @@ CC_FLAGS_REMOVE_VDSO := $(CC_FLAGS_FTRACE) -Os > >>>>> $(CC_FLAGS_SCS) \ > >>>>> $(CC_FLAGS_LTO) $(CC_FLAGS_CFI) \ > >>>>> -Wmissing-prototypes -Wmissing-declarations > >>>>> > >>>>> -CC_FLAGS_ADD_VDSO := -O2 -mcmodel=tiny -fasynchronous-unwind-tables > >>>>> +CC_FLAGS_ADD_VDSO := -O2 -mcmodel=tiny -fasynchronous-unwind-tables > >>>>> $(CONFIG_CC_OPT_INLINE_MEMSET) > >>>>> > >>>>> CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_REMOVE_VDSO) > >>>>> CFLAGS_REMOVE_vgetrandom.o = $(CC_FLAGS_REMOVE_VDSO) > >>>>> diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile > >>>>> index 9c9181bb4071..0b84892d084b 100644 > >>>>> --- a/arch/loongarch/vdso/Makefile > >>>>> +++ b/arch/loongarch/vdso/Makefile > >>>>> @@ -16,6 +16,7 @@ ccflags-vdso := \ > >>>>> $(filter -m64,$(KBUILD_CFLAGS)) \ > >>>>> $(filter -march=%,$(KBUILD_CFLAGS)) \ > >>>>> $(filter -m%-float,$(KBUILD_CFLAGS)) \ > >>>>> + $(CONFIG_CC_OPT_INLINE_MEMSET) \ > >>>>> $(CLANG_FLAGS) \ > >>>>> -D__VDSO__ > >>>>> > >>>>> diff --git a/arch/powerpc/kernel/vdso/Makefile > >>>>> b/arch/powerpc/kernel/vdso/Makefile > >>>>> index 368759f81708..0d1a49529885 100644 > >>>>> --- a/arch/powerpc/kernel/vdso/Makefile > >>>>> +++ b/arch/powerpc/kernel/vdso/Makefile > >>>>> @@ -43,6 +43,7 @@ ccflags-y := -fno-common -fno-builtin -DBUILD_VDSO > >>>>> ccflags-y += $(DISABLE_LATENT_ENTROPY_PLUGIN) > >>>>> ccflags-y += $(call cc-option, -fno-stack-protector) > >>>>> ccflags-y += -DDISABLE_BRANCH_PROFILING > >>>>> +ccflags-y += $(CONFIG_CC_OPT_INLINE_MEMSET) > >>>>> ccflags-y += -ffreestanding -fasynchronous-unwind-tables > >>>>> ccflags-remove-y := $(CC_FLAGS_FTRACE) > >>>>> ldflags-y := -Wl,--hash-style=both -nostdlib -shared -z noexecstack > >>>>> $(CLANG_FLAGS) > >>>>> diff --git a/arch/riscv/kernel/vdso/Makefile > >>>>> b/arch/riscv/kernel/vdso/Makefile > >>>>> index 8dbf2532a573..c023046a3fd7 100644 > >>>>> --- a/arch/riscv/kernel/vdso/Makefile > >>>>> +++ b/arch/riscv/kernel/vdso/Makefile > >>>>> @@ -36,6 +36,7 @@ endif > >>>>> ccflags-y := -fno-stack-protector > >>>>> ccflags-y += -DDISABLE_BRANCH_PROFILING > >>>>> ccflags-y += -fno-builtin > >>>>> +ccflags-y += $(CONFIG_CC_OPT_INLINE_MEMSET) > >>>>> ccflags-y += $(KBUILD_BASE_ISA)$(CFI_MARCH) > >>>>> ccflags-y += $(CFI_FULL) > >>>>> asflags-y += $(KBUILD_BASE_ISA)$(CFI_MARCH) > >>>>> diff --git a/arch/s390/kernel/vdso/Makefile > >>>>> b/arch/s390/kernel/vdso/Makefile > >>>>> index 35c834b895ec..54bcf2984ca1 100644 > >>>>> --- a/arch/s390/kernel/vdso/Makefile > >>>>> +++ b/arch/s390/kernel/vdso/Makefile > >>>>> @@ -29,6 +29,7 @@ KBUILD_CFLAGS_VDSO := $(filter-out > >>>>> -munaligned-symbols,$(KBUILD_CFLAGS_VDSO)) > >>>>> KBUILD_CFLAGS_VDSO := $(filter-out > >>>>> -fno-asynchronous-unwind-tables,$(KBUILD_CFLAGS_VDSO)) > >>>>> KBUILD_CFLAGS_VDSO += -fPIC -fno-common -fno-builtin > >>>>> -fasynchronous-unwind-tables > >>>>> KBUILD_CFLAGS_VDSO += -fno-stack-protector $(DISABLE_KSTACK_ERASE) > >>>>> +KBUILD_CFLAGS_VDSO += $(CONFIG_CC_OPT_INLINE_MEMSET) > >>>>> ldflags-y := -shared -soname=linux-vdso.so.1 \ > >>>>> --hash-style=both --build-id=sha1 \ > >>>>> $(call ld-option, --eh-frame-hdr) -T > >>>>> diff --git a/arch/x86/entry/vdso/vdso64/Makefile > >>>>> b/arch/x86/entry/vdso/vdso64/Makefile > >>>>> index 7c0790065b5e..c2353a065279 100644 > >>>>> --- a/arch/x86/entry/vdso/vdso64/Makefile > >>>>> +++ b/arch/x86/entry/vdso/vdso64/Makefile > >>>>> @@ -14,7 +14,7 @@ vobjs-$(CONFIG_X86_SGX) += > >>>>> vsgx.o > >>>>> vobjs-$(CONFIG_FUTEX_ROBUST_UNLOCK) += vfutex.o > >>>>> > >>>>> # Compilation flags > >>>>> -flags-y := -DBUILD_VDSO64 -m64 > >>>>> -mcmodel=small > >>>>> +flags-y := -DBUILD_VDSO64 -m64 > >>>>> -mcmodel=small $(CONFIG_CC_OPT_INLINE_MEMSET) > >>>>> > >>>>> # The location of this include matters! > >>>>> include $(src)/../common/Makefile.include > >>>>> diff --git a/init/Kconfig b/init/Kconfig > >>>>> index 8583d9f06c52..ff3f8475dd2f 100644 > >>>>> --- a/init/Kconfig > >>>>> +++ b/init/Kconfig > >>>>> @@ -173,6 +173,13 @@ 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_HAS_OPT_INLINE_MEMSET > >>>>> + def_bool $(cc-option,-finline-stringops=memset) > >>>>> + > >>>>> +config CC_OPT_INLINE_MEMSET > >>>>> + string > >>>>> + default "-finline-stringops=memset" if CC_HAS_OPT_INLINE_MEMSET > >>>>> + > >>>>> config LD_CAN_USE_KEEP_IN_OVERLAY > >>>>> # ld.lld prior to 21.0.0 did not support KEEP within an > >>>>> overlay description > >>>>> # > >>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fpull%2F130661&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659727352%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=03eAQvPTDs%2FN28bYiiZAVYcx2JFSkuOM7x2iwFU%2F%2FxA%3D&reserved=0 > >>>>> diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c > >>>>> index 2851afa9154f..f5cad5641985 100644 > >>>>> --- a/lib/vdso/getrandom.c > >>>>> +++ b/lib/vdso/getrandom.c > >>>>> @@ -29,6 +29,22 @@ > >>>>> } > >>>>> \ > >>>>> } while (0) > >>>>> > >>>>> +#if __has_builtin(__builtin_memset_inline) > >>>>> +#define memset_inline(dst, value, size) __builtin_memset_inline(dst, > >>>>> value, size) > >>>>> +#elif IS_ENABLED(CONFIG_CC_HAS_OPT_INLINE_MEMSET) > >>>>> +#define memset_inline(dst, value, size) __builtin_memset(dst, value, > >>>>> size) > >>>>> +#else > >>>>> +static inline void *memset_inline(void *dst, int value, size_t size) > >>>>> +{ > >>>>> + char *d = dst; > >>>>> + > >>>>> + while (size--) > >>>>> + *d++ = value; > >>>>> + > >>>>> + return d; > >>>>> +} > >>>>> +#endif > >>>> > >>>> Does this work? > >>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgodbolt.org%2Fz%2FTx6EaGMfb&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659741160%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Xv0rle85Js5BH2qNUL4q2Iv2ZwgJhJ4FaTuHYAvvEVo%3D&reserved=0 > >>> > >>> Hmmm...possibly. > >>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgodbolt.org%2Fz%2Fec9rzd9Yf&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659754022%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=bLajY6c3CbYOZMJlBA4bYlVE3bNVc%2Fxe1KYk0rUJgjM%3D&reserved=0 > >>> I don't get it... > >> > >> Just keep it under 2 pages, it will be fine: > >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgodbolt.org%2Fz%2FqqoMqfxev&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659763804%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Bcp1%2B%2Fir05tsPwf08OQkJx4vDkPliaSppam1e%2BTPprk%3D&reserved=0 > > > > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgodbolt.org%2Fz%2F9W9f5a7Wx&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4df96063ffd94e6204df08df1bb54e3d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639260137659773169%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=YPGYXcKrnM4e1Q2nHdshRUaMT36w%2BRkHuIWIgcbpA94%3D&reserved=0 > > > > Apparently not on RISCV, which is what prompted this patch in the first > > place. So I suspect Nathan's v2 here is the way to go. > > > Don't you have -fno-builtin on RISCV like we have on powerpc ?
I think Nick mentioned this led to other problems and didn't exactly solve the problem.
