syscalls: Remove start and number from syscall_get_arguments() args

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>

1 files changed, 6 insertions, 33 deletions

diff --git a/arch/um/include/asm/syscall-generic.h b/arch/um/include/asm/syscall-generic.h
index 9fb9cf8cd39a..25d00acd1322 100644
--- a/arch/um/include/asm/syscall-generic.h
+++ b/arch/um/include/asm/syscall-generic.h
@@ -53,43 +53,16 @@ static inline void syscall_set_return_value(struct task_struct *task,
 
 static inline void syscall_get_arguments(struct task_struct *task,
                                          struct pt_regs *regs,
-                                         unsigned int i, unsigned int n,
                                          unsigned long *args)
 {
         const struct uml_pt_regs *r = &regs->regs;
 
-        switch (i) {
-        case 0:
-                if (!n--)
-                        break;
-                *args++ = UPT_SYSCALL_ARG1(r);
-        case 1:
-                if (!n--)
-                        break;
-                *args++ = UPT_SYSCALL_ARG2(r);
-        case 2:
-                if (!n--)
-                        break;
-                *args++ = UPT_SYSCALL_ARG3(r);
-        case 3:
-                if (!n--)
-                        break;
-                *args++ = UPT_SYSCALL_ARG4(r);
-        case 4:
-                if (!n--)
-                        break;
-                *args++ = UPT_SYSCALL_ARG5(r);
-        case 5:
-                if (!n--)
-                        break;
-                *args++ = UPT_SYSCALL_ARG6(r);
-        case 6:
-                if (!n--)
-                        break;
-        default:
-                BUG();
-                break;
-        }
+        *args++ = UPT_SYSCALL_ARG1(r);
+        *args++ = UPT_SYSCALL_ARG2(r);
+        *args++ = UPT_SYSCALL_ARG3(r);
+        *args++ = UPT_SYSCALL_ARG4(r);
+        *args++ = UPT_SYSCALL_ARG5(r);
+        *args   = UPT_SYSCALL_ARG6(r);
 }
 
 static inline void syscall_set_arguments(struct task_struct *task,