linux-kernel - [RFC PATCH v1 1/1] arm64: add compile-time test into is_compat

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Message-ID: <20240104192433.109983-2-leobras@redhat.com>
Date: Thu,  4 Jan 2024 16:24:33 -0300
From: Leonardo Bras <leobras@...hat.com>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Ard Biesheuvel <ardb@...nel.org>,
	Teo Couprie Diaz <teo.coupriediaz@....com>,
	Leonardo Bras <leobras@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Mark Brown <broonie@...nel.org>,
	"Steven Rostedt (Google)" <rostedt@...dmis.org>,
	Guo Hui <guohui@...ontech.com>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v1 1/1] arm64: add compile-time test into is_compat_task()

Currently some parts of the codebase will test for CONFIG_COMPAT before
testing is_compat_task(), probably in order to avoid a run-time test into
the task structure, while other parts of codebase will just test even when
the option is not compiled in.

Since is_compat_task() is an inlined function, it would be helpful to add a
!CONFIG_COMPAT version of the helper, allowing compile-time optimization.

With this, the compiler is able to understand in build-time that
is_compat_task() will always return 0, and optimize-out some of the extra
code introduced by the option.

This allows optimizing-out code when the option is not selected, and
otherwise removing a lot #ifdefs that were introduced, making the code
more clean.

Signed-off-by: Leonardo Bras <leobras@...hat.com>
---
 arch/arm64/include/asm/compat.h | 5 +++++
 arch/arm64/kernel/ptrace.c      | 6 ++----
 arch/arm64/kernel/syscall.c     | 5 +----
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/compat.h b/arch/arm64/include/asm/compat.h
index ae904a1ad5293..3cc61cbbb9062 100644
--- a/arch/arm64/include/asm/compat.h
+++ b/arch/arm64/include/asm/compat.h
@@ -100,6 +100,11 @@ long compat_arm_syscall(struct pt_regs *regs, int scno);
 
 #else /* !CONFIG_COMPAT */
 
+static inline int is_compat_task(void)
+{
+	return 0;
+}
+
 static inline int is_compat_thread(struct thread_info *thread)
 {
 	return 0;
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 20d7ef82de90a..9f8781f1fdfda 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -173,7 +173,6 @@ static void ptrace_hbptriggered(struct perf_event *bp,
 	struct arch_hw_breakpoint *bkpt = counter_arch_bp(bp);
 	const char *desc = "Hardware breakpoint trap (ptrace)";
 
-#ifdef CONFIG_COMPAT
 	if (is_compat_task()) {
 		int si_errno = 0;
 		int i;
@@ -195,7 +194,7 @@ static void ptrace_hbptriggered(struct perf_event *bp,
 						  desc);
 		return;
 	}
-#endif
+
 	arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, bkpt->trigger, desc);
 }
 
@@ -2112,7 +2111,6 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 
 const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 {
-#ifdef CONFIG_COMPAT
 	/*
 	 * Core dumping of 32-bit tasks or compat ptrace requests must use the
 	 * user_aarch32_view compatible with arm32. Native ptrace requests on
@@ -2123,7 +2121,7 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 		return &user_aarch32_view;
 	else if (is_compat_thread(task_thread_info(task)))
 		return &user_aarch32_ptrace_view;
-#endif
+
 	return &user_aarch64_view;
 }
 
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 9a70d9746b661..ad198262b9817 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -20,14 +20,11 @@ long sys_ni_syscall(void);
 
 static long do_ni_syscall(struct pt_regs *regs, int scno)
 {
-#ifdef CONFIG_COMPAT
-	long ret;
 	if (is_compat_task()) {
-		ret = compat_arm_syscall(regs, scno);
+		long ret = compat_arm_syscall(regs, scno);
 		if (ret != -ENOSYS)
 			return ret;
 	}
-#endif
 
 	return sys_ni_syscall();
 }
-- 
2.43.0