From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F55D38D01B; Sat, 26 Sep 2026 06:34:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790404461; cv=none; b=Vp+NkSBYqM0b7U+fFfeDmNRA5iVfZY9qJjaElVoLSkJgv17P55e0e9T54urIEcMfj1hYB74Emjcw/SMFdVAILtQxkQ83ED3QY+Sc1RZPM//OIWuzb6LovOzrNtU0foMUkkJYHT+q2V8wTq82NgZObFa5oFtuUuMTU9Tll+VULVw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790404461; c=relaxed/simple; bh=EM8Aq0zba55JAF1PiqJZKwXUK24rdLNa8m9H7uIa2tU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LrnJHnCJ9x0qrsChV7c7MnUgi4wrbh6l9bnwTYR3xrGlfZ+3R9C66eT+uyqAf1e5icrKTbKmIl0qSxv3ciFyDKBQa17ATnkOpp78kAi+qkFXjzc46pqAZs74+EgK8YjYNZGjL0W8AYsjQUJoNWctLrpHrQGEaAlBUNBgQTplD0E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=X3keQOxp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="X3keQOxp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C00571F000FF; Sat, 26 Sep 2026 06:34:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790404459; bh=PGoBOYGQFMmgkg0THkTOdUI30C4ST2Titdv6ASdq6z8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=X3keQOxp1tBtuWVBA/GBtSTLiUQRxOBSNxRdAlOlbGfr7T3RKDQAP1hU9UbGqlC/w 3PJ85mcmhlsLwmq6yVlRoD28izVuDgabWq/+5UM7kpOBE3Pk4Go9B9ehwO9gn0Bhev iTAl61Ikfsa33CGlRO1QkLudvPEperBl2X1NsI2lSzQMy65KohW5DWudmwPtA2CcV2 T66a7nZlZZzbltX3v1DTuvDm+99chPB2HuXc5lYYlWIkTQ+0UMV3AL4FjdI7+rMVN7 OF4JtgtAHZvxID7lezJ9eYLLkQQUepVcO0JWZGTfrVT0/Q7Lnt+hslscKk5CoLHGie QdYcU5p96v9XQ== Message-ID: <76f4039a-d591-4b6a-af7e-83eb90266719@kernel.org> Date: Sat, 26 Sep 2026 08:34:06 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data() To: Nick Desaulniers , Nathan Chancellor Cc: Andy Lutomirski , Thomas Gleixner , Theodore Ts'o , "Jason A. Donenfeld" , Vincenzo Frascino , Bill Wendling , Justin Stitt , Catalin Marinas , Will Deacon , Mark Rutland , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, llvm@lists.linux.dev References: <20260925-vdso-getrandom-avoid-memset-llvm-24-v2-1-ce640f872393@kernel.org> Content-Language: fr-FR From: "Christophe Leroy (CS GROUP)" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Le 26/09/2026 à 00:00, Nick Desaulniers a écrit : > On Fri, Sep 25, 2026 at 2:56 PM Nick Desaulniers > wrote: >> >> On Fri, Sep 25, 2026 at 2:53 PM Nick Desaulniers >> wrote: >>> >>> On Fri, Sep 25, 2026 at 2:46 PM Nathan Chancellor 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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683663121%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=TzFmsIf6K0ZNffmwZjFRWcrFHJ4akhMw%2FxcWeHR4hFY%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683681786%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=A6PdZfaF0MvKQ0TEuJEnFWmXpMKD5CPz6Ko2fWh9ZGY%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683693796%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=ordMFwd99jKGsM6%2F5jqb6T%2FCzJZ%2BccJTNL6Zyyz38S4%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683704121%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=mqgeAxJp0cTsBD1qngk%2BliTUC1kID648Z81H6hiKYDI%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683713563%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=hNiJSMBbn6k7Pq4uBYQ5Bi6fO8ttW8KXVK6hPLEfJCM%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683722844%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=BwB1lUSynGcGGLwkspnlVbkBAkdeRo4ItXk19ffMU44%3D&reserved=0 [6] >>>> Suggested-by: "Jason A. Donenfeld" >>>> Suggested-by: Nick Desaulniers >>>> Signed-off-by: Nathan Chancellor >>>> --- >>>> 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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683731836%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Z1w8wFKZCVjlUIwkIjffeIBIPkDhRRln3l7xot3daRc%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683740883%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=JlYxG81FQsC5sm3aLe4M6uUIaU5QNmdbupcy3LuGPGQ%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683749874%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=3MCx7IwcEz2ieYYZzQ2dLdrxFTjJiUqH0c1qiOXeLlo%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683758681%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=5T4oq%2B4AfVJBqvBNA19kzNq19kRYM9u8YzYcP%2B8P7Mw%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%7C8130be3fe7304659b8e308df1b507f25%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639259704683768107%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=FrwGHnEXsSp8scH8GtL%2BlqjymHfVokSrtaOqhp2iZPg%3D&reserved=0 > Doesn't work on powerpc (gcc 13.4): foo: li 5,8192 li 4,0 b memset foo2: li 5,8193 li 4,0 b memset But that's the reason why vdso Makefile has option -fno-builtin, that option gives instead: foo: li 10,2048 li 9,0 addi 3,3,-1 mtctr 10 .L2: stb 9,1(3) stb 9,2(3) stb 9,3(3) stbu 9,4(3) bdnz .L2 blr foo2: li 9,0 li 10,2048 stb 9,0(3) mtctr 10 .L10: stb 9,1(3) stb 9,2(3) stb 9,3(3) stbu 9,4(3) bdnz .L10 blr Christophe