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Peter Anvin" Subject: [PATCH] x86/kexec: store segment registers directly to memory in crash_setup_regs() Date: Wed, 25 Mar 2026 10:29:33 +0100 Message-ID: <20260325092959.55946-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" crash_setup_regs() currently moves segment registers (ss, cs, ds, es) into pt_regs via a general purpose register (%eax). Update the code to avoid the intermediate register and store segment registers directly to their destination fields. This reduces the generated code from: 131: 8c d0 mov %ss,%eax 133: 66 89 84 24 a0 00 00 mov %ax,0xa0(%rsp) 13a: 00 13b: 8c c8 mov %cs,%eax 13d: 66 89 84 24 88 00 00 mov %ax,0x88(%rsp) 144: 00 to: 131: 8c 94 24 a0 00 00 00 mov %ss,0xa0(%rsp) 138: 8c 8c 24 88 00 00 00 mov %cs,0x88(%rsp) No functional change intended. Signed-off-by: Uros Bizjak Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" --- arch/x86/include/asm/kexec.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h index 5cfb27f26583..ad7ef567452b 100644 --- a/arch/x86/include/asm/kexec.h +++ b/arch/x86/include/asm/kexec.h @@ -106,11 +106,11 @@ static inline void crash_setup_regs(struct pt_regs *n= ewregs, asm volatile("mov %%r14,%0" : "=3Dm"(newregs->r14)); asm volatile("mov %%r15,%0" : "=3Dm"(newregs->r15)); #endif - asm volatile("mov %%ss,%k0" : "=3Da"(newregs->ss)); - asm volatile("mov %%cs,%k0" : "=3Da"(newregs->cs)); + asm volatile("mov %%ss,%0" : "=3Dm"(newregs->ss)); + asm volatile("mov %%cs,%0" : "=3Dm"(newregs->cs)); #ifdef CONFIG_X86_32 - asm volatile("mov %%ds,%k0" : "=3Da"(newregs->ds)); - asm volatile("mov %%es,%k0" : "=3Da"(newregs->es)); + asm volatile("mov %%ds,%0" : "=3Dm"(newregs->ds)); + asm volatile("mov %%es,%0" : "=3Dm"(newregs->es)); #endif asm volatile("pushf\n\t" "pop %0" : "=3Dm"(newregs->flags)); --=20 2.53.0