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[5.147.80.91]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b76fcacf0bsm4109538f8f.38.2025.07.24.23.26.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Jul 2025 23:26:41 -0700 (PDT) Message-ID: <0532c555-1876-449b-89cb-36ce5394433f@canonical.com> Date: Fri, 25 Jul 2025 08:26:39 +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 03/11] riscv: indirect jmp in asm that's static in nature to use sw guarded jump To: Deepak Gupta , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nick Desaulniers , Bill Wendling , Monk Chiang , Kito Cheng , Justin Stitt Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, rick.p.edgecombe@intel.com, broonie@kernel.org, cleger@rivosinc.com, samitolvanen@google.com, apatel@ventanamicro.com, ajones@ventanamicro.com, conor.dooley@microchip.com, charlie@rivosinc.com, samuel.holland@sifive.com, bjorn@rivosinc.com, fweimer@redhat.com, jeffreyalaw@gmail.com, andrew@sifive.com, ved@rivosinc.com References: <20250724-riscv_kcfi-v1-0-04b8fa44c98c@rivosinc.com> <20250724-riscv_kcfi-v1-3-04b8fa44c98c@rivosinc.com> Content-Language: en-US From: Heinrich Schuchardt In-Reply-To: <20250724-riscv_kcfi-v1-3-04b8fa44c98c@rivosinc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 25.07.25 01:36, Deepak Gupta wrote: > Handwritten `__memset` asm routine perform static jumps within > function and uses `a5` to do that. This would require a landing pad > instruction at the target. Since its static jump and no memory load is > involved, use `t2` instead which is exempt from requiring a landing pad. > > Signed-off-by: Deepak Gupta Acked-by: Heinrich Schuchardt > --- > arch/riscv/lib/memset.S | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/riscv/lib/memset.S b/arch/riscv/lib/memset.S > index da23b8347e2d..c4a318d8eef3 100644 > --- a/arch/riscv/lib/memset.S > +++ b/arch/riscv/lib/memset.S > @@ -56,12 +56,12 @@ SYM_FUNC_START(__memset) > > /* Jump into loop body */ > /* Assumes 32-bit instruction lengths */ > - la a5, 3f > + la t2, 3f > #ifdef CONFIG_64BIT > srli a4, a4, 1 > #endif > - add a5, a5, a4 > - jr a5 > + add t2, t2, a4 > + jr t2 > 3: > REG_S a1, 0(t0) > REG_S a1, SZREG(t0) >