Re: [PATCH v2 1/1] arm64: make a single hook to syscall_trace() for all syscall features

On 02/26/2014 12:00 AM, Will Deacon wrote: > On Tue, Feb 25, 2014 at 09:14:43AM +0000, AKASHI Takahiro wrote: >> Currently syscall_trace() is called only for ptrace. >> With additional TIF_xx flags defined, it is now called in all the cases >> of audit, ftrace and seccomp in addition to ptrace. >> >> Signed-off-by: AKASHI Takahiro <takahiro.akashi(a)linaro.org&gt; >> Acked-by: Richard Guy Briggs <rgb(a)redhat.com&gt; >> --- >> arch/arm64/include/asm/thread_info.h | 13 ++++++++++ >> arch/arm64/kernel/entry.S | 5 ++-- >> arch/arm64/kernel/ptrace.c | 45 +++++++++++++++++----------------- >> 3 files changed, 38 insertions(+), 25 deletions(-) [...] >> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c >> index 6a8928b..c70133e 100644 >> --- a/arch/arm64/kernel/ptrace.c >> +++ b/arch/arm64/kernel/ptrace.c >> @@ -1062,31 +1062,30 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs) >> { >> unsigned long saved_reg; >> >> - if (!test_thread_flag(TIF_SYSCALL_TRACE)) >> - return regs->syscallno; >> - >> - if (is_compat_task()) { >> - /* AArch32 uses ip (r12) for scratch */ >> - saved_reg = regs->regs[12]; >> - regs->regs[12] = dir; >> - } else { >> - /* >> - * Save X7. X7 is used to denote syscall entry/exit: >> - * X7 = 0 -> entry, = 1 -> exit >> - */ >> - saved_reg = regs->regs[7]; >> - regs->regs[7] = dir; >> - } >> + if (test_thread_flag(TIF_SYSCALL_TRACE)) { >> + if (is_compat_task()) { >> + /* AArch32 uses ip (r12) for scratch */ >> + saved_reg = regs->regs[12]; >> + regs->regs[12] = dir; >> + } else { >> + /* >> + * Save X7. X7 is used to denote syscall entry/exit: >> + * X7 = 0 -> entry, = 1 -> exit >> + */ >> + saved_reg = regs->regs[7]; >> + regs->regs[7] = dir; >> + } >> >> - if (dir) >> - tracehook_report_syscall_exit(regs, 0); >> - else if (tracehook_report_syscall_entry(regs)) >> - regs->syscallno = ~0UL; >> + if (dir) >> + tracehook_report_syscall_exit(regs, 0); >> + else if (tracehook_report_syscall_entry(regs)) >> + regs->syscallno = ~0UL; >> >> - if (is_compat_task()) >> - regs->regs[12] = saved_reg; >> - else >> - regs->regs[7] = saved_reg; >> + if (is_compat_task()) >> + regs->regs[12] = saved_reg; >> + else >> + regs->regs[7] = saved_reg; >> + } > > Aren't these changes (to ptrace.c) just a giant NOP? Umm, the purpose of this big "if" is to run the code only if TIF_SYSCALL_TRACE is set, and to make it easy to add additional hooks, audit and ftrace, around tracehook_report_*() later on.