On Mon, Apr 01, 2019 at 09:41:09AM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx> > > 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@xxxxxxxxxxx FWIW, you can add Reviewed-by: Dmitry V. Levin <ldv@xxxxxxxxxxxx> There are several places listed below where I'd prefer to see more readable equivalents, but feel free to leave it to respective arch maintainers. > diff --git a/arch/hexagon/include/asm/syscall.h b/arch/hexagon/include/asm/syscall.h > index 4af9c7b6f13a..ae3a1e24fabd 100644 > --- a/arch/hexagon/include/asm/syscall.h > +++ b/arch/hexagon/include/asm/syscall.h > @@ -37,10 +37,8 @@ static inline long syscall_get_nr(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) > { > - BUG_ON(i + n > 6); > - memcpy(args, &(®s->r00)[i], n * sizeof(args[0])); > + memcpy(args, &(®s->r00)[0], 6 * sizeof(args[0])); A shorter and slightly more readable equivalent is memcpy(args, ®s->r00, 6 * sizeof(args[0])); > diff --git a/arch/nds32/include/asm/syscall.h b/arch/nds32/include/asm/syscall.h > index f7e5e86765fe..89a6ec8731d8 100644 > --- a/arch/nds32/include/asm/syscall.h > +++ b/arch/nds32/include/asm/syscall.h > @@ -108,42 +108,21 @@ void syscall_set_return_value(struct task_struct *task, struct pt_regs *regs, > * syscall_get_arguments - extract system call parameter values > * @task: task of interest, must be blocked > * @regs: task_pt_regs() of @task > - * @i: argument index [0,5] > - * @n: number of arguments; n+i must be [1,6]. > * @args: array filled with argument values > * > - * Fetches @n arguments to the system call starting with the @i'th argument > - * (from 0 through 5). Argument @i is stored in @args[0], and so on. > - * An arch inline version is probably optimal when @i and @n are constants. > + * Fetches 6 arguments to the system call (from 0 through 5). The first > + * argument is stored in @args[0], and so on. > * > * It's only valid to call this when @task is stopped for tracing on > * entry to a system call, due to %TIF_SYSCALL_TRACE or %TIF_SYSCALL_AUDIT. > - * It's invalid to call this with @i + @n > 6; we only support system calls > - * taking up to 6 arguments. > */ > #define SYSCALL_MAX_ARGS 6 > void syscall_get_arguments(struct task_struct *task, struct pt_regs *regs, > - unsigned int i, unsigned int n, unsigned long *args) > + unsigned long *args) > { > - if (n == 0) > - return; > - if (i + n > SYSCALL_MAX_ARGS) { > - unsigned long *args_bad = args + SYSCALL_MAX_ARGS - i; > - unsigned int n_bad = n + i - SYSCALL_MAX_ARGS; > - pr_warning("%s called with max args %d, handling only %d\n", > - __func__, i + n, SYSCALL_MAX_ARGS); > - memset(args_bad, 0, n_bad * sizeof(args[0])); > - memset(args_bad, 0, n_bad * sizeof(args[0])); > - } > - > - if (i == 0) { > - args[0] = regs->orig_r0; > - args++; > - i++; > - n--; > - } > - > - memcpy(args, ®s->uregs[0] + i, n * sizeof(args[0])); > + args[0] = regs->orig_r0; > + args++; > + memcpy(args, ®s->uregs[0] + 1, 5 * sizeof(args[0])); > } A shorter and slightly more readable equivalent of the last memcpy is memcpy(args, ®s->uregs[1], 5 * sizeof(args[0])); > diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h > index 1a0e7a8b1c81..5c9b9dc82b7e 100644 > --- a/arch/powerpc/include/asm/syscall.h > +++ b/arch/powerpc/include/asm/syscall.h > @@ -65,22 +65,20 @@ 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) > { > unsigned long val, mask = -1UL; > - > - BUG_ON(i + n > 6); > + unsigned int n = 6; > > #ifdef CONFIG_COMPAT > if (test_tsk_thread_flag(task, TIF_32BIT)) > mask = 0xffffffff; > #endif > while (n--) { > - if (n == 0 && i == 0) > + if (n == 0) > val = regs->orig_gpr3; > else > - val = regs->gpr[3 + i + n]; > + val = regs->gpr[3 + n]; > > args[n] = val & mask; > } A shorter and slightly more readable equivalent of the loop is while (--n) args[n] = regs->gpr[3 + n] & mask; args[0] = regs->orig_gpr3 & mask; > diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h > index 96f9a9151fde..ee0b1f6aa36d 100644 > --- a/arch/s390/include/asm/syscall.h > +++ b/arch/s390/include/asm/syscall.h > @@ -56,27 +56,20 @@ 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) > { > unsigned long mask = -1UL; > + unsigned int n = 6; > > - /* > - * No arguments for this syscall, there's nothing to do. > - */ > - if (!n) > - return; > - > - BUG_ON(i + n > 6); > #ifdef CONFIG_COMPAT > if (test_tsk_thread_flag(task, TIF_31BIT)) > mask = 0xffffffff; > #endif > while (n-- > 0) > - if (i + n > 0) > - args[n] = regs->gprs[2 + i + n] & mask; > - if (i == 0) > - args[0] = regs->orig_gpr2 & mask; > + if (n > 0) > + args[n] = regs->gprs[2 + n] & mask; > + > + args[0] = regs->orig_gpr2 & mask; A shorter and slightly more readable equivalent of the loop is while (--n > 0) args[n] = regs->gprs[2 + n] & mask; -- ldv
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