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At Linux Plumbers, Andy Lutomirski approached me and pointed out that the function call syscall_get_arguments() implemented in x86 was horribly written and not optimized for the standard case of passing in 0 and 6 for the starting index and the number of system calls to get. When looking at all the users of this function, I discovered that all instances pass in only 0 and 6 for these arguments. Instead of having this function handle different cases that are never used, simply rewrite it to return the first 6 arguments of a system call. This should help out the performance of tracing system calls by ptrace, ftrace and perf. Link: http://lkml.kernel.org/r/20161107213233.754809394@goodmis.org Cc: Oleg Nesterov <oleg@redhat.com> Cc: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Dominik Brodowski <linux@dominikbrodowski.net> Cc: Dave Martin <dave.martin@arm.com> Cc: "Dmitry V. Levin" <ldv@altlinux.org> Cc: x86@kernel.org Cc: linux-snps-arc@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-c6x-dev@linux-c6x.org Cc: uclinux-h8-devel@lists.sourceforge.jp Cc: linux-hexagon@vger.kernel.org Cc: linux-ia64@vger.kernel.org Cc: linux-mips@vger.kernel.org Cc: nios2-dev@lists.rocketboards.org Cc: openrisc@lists.librecores.org Cc: linux-parisc@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-riscv@lists.infradead.org Cc: linux-s390@vger.kernel.org Cc: linux-sh@vger.kernel.org Cc: sparclinux@vger.kernel.org Cc: linux-um@lists.infradead.org Cc: linux-xtensa@linux-xtensa.org Cc: linux-arch@vger.kernel.org Acked-by: Paul Burton <paul.burton@mips.com> # MIPS parts Acked-by: Max Filippov <jcmvbkbc@gmail.com> # For xtensa changes Acked-by: Will Deacon <will.deacon@arm.com> # For the arm64 bits Reviewed-by: Thomas Gleixner <tglx@linutronix.de> # for x86 Reviewed-by: Dmitry V. Levin <ldv@altlinux.org> Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
81 lines
2.5 KiB
C
81 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/ptrace.h>
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#include <linux/sched.h>
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#include <linux/sched/task_stack.h>
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#include <linux/export.h>
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#include <asm/syscall.h>
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static int collect_syscall(struct task_struct *target, struct syscall_info *info)
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{
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struct pt_regs *regs;
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if (!try_get_task_stack(target)) {
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/* Task has no stack, so the task isn't in a syscall. */
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memset(info, 0, sizeof(*info));
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info->data.nr = -1;
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return 0;
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}
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regs = task_pt_regs(target);
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if (unlikely(!regs)) {
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put_task_stack(target);
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return -EAGAIN;
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}
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info->sp = user_stack_pointer(regs);
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info->data.instruction_pointer = instruction_pointer(regs);
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info->data.nr = syscall_get_nr(target, regs);
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if (info->data.nr != -1L)
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syscall_get_arguments(target, regs,
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(unsigned long *)&info->data.args[0]);
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put_task_stack(target);
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return 0;
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}
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/**
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* task_current_syscall - Discover what a blocked task is doing.
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* @target: thread to examine
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* @info: structure with the following fields:
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* .sp - filled with user stack pointer
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* .data.nr - filled with system call number or -1
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* .data.args - filled with @maxargs system call arguments
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* .data.instruction_pointer - filled with user PC
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*
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* If @target is blocked in a system call, returns zero with @info.data.nr
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* set to the the call's number and @info.data.args filled in with its
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* arguments. Registers not used for system call arguments may not be available
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* and it is not kosher to use &struct user_regset calls while the system
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* call is still in progress. Note we may get this result if @target
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* has finished its system call but not yet returned to user mode, such
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* as when it's stopped for signal handling or syscall exit tracing.
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*
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* If @target is blocked in the kernel during a fault or exception,
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* returns zero with *@info.data.nr set to -1 and does not fill in
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* @info.data.args. If so, it's now safe to examine @target using
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* &struct user_regset get() calls as long as we're sure @target won't return
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* to user mode.
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*
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* Returns -%EAGAIN if @target does not remain blocked.
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*/
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int task_current_syscall(struct task_struct *target, struct syscall_info *info)
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{
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long state;
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unsigned long ncsw;
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if (target == current)
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return collect_syscall(target, info);
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state = target->state;
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if (unlikely(!state))
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return -EAGAIN;
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ncsw = wait_task_inactive(target, state);
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if (unlikely(!ncsw) ||
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unlikely(collect_syscall(target, info)) ||
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unlikely(wait_task_inactive(target, state) != ncsw))
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return -EAGAIN;
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return 0;
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}
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