Re: [PATCH] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call

From: kbuild test robot
Date: Sat Nov 10 2018 - 07:06:26 EST


Hi Elvira,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on powerpc/next]
[also build test WARNING on v4.20-rc1 next-20181109]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Elvira-Khabirova/powerpc-ptrace-replace-ptrace_report_syscall-with-a-tracehook-call/20181110-192337
base: https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
config: powerpc-allyesconfig (attached as .config)
compiler: powerpc64-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
GCC_VERSION=7.2.0 make.cross ARCH=powerpc

All warnings (new ones prefixed by >>):

arch/powerpc/kernel/ptrace.c: In function 'do_syscall_trace_enter':
>> arch/powerpc/kernel/ptrace.c:3269:3: warning: ignoring return value of 'tracehook_report_syscall_entry', declared with attribute warn_unused_result [-Wunused-result]
tracehook_report_syscall_entry(regs);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

vim +/tracehook_report_syscall_entry +3269 arch/powerpc/kernel/ptrace.c

3244
3245 /**
3246 * do_syscall_trace_enter() - Do syscall tracing on kernel entry.
3247 * @regs: the pt_regs of the task to trace (current)
3248 *
3249 * Performs various types of tracing on syscall entry. This includes seccomp,
3250 * ptrace, syscall tracepoints and audit.
3251 *
3252 * The pt_regs are potentially visible to userspace via ptrace, so their
3253 * contents is ABI.
3254 *
3255 * One or more of the tracers may modify the contents of pt_regs, in particular
3256 * to modify arguments or even the syscall number itself.
3257 *
3258 * It's also possible that a tracer can choose to reject the system call. In
3259 * that case this function will return an illegal syscall number, and will put
3260 * an appropriate return value in regs->r3.
3261 *
3262 * Return: the (possibly changed) syscall number.
3263 */
3264 long do_syscall_trace_enter(struct pt_regs *regs)
3265 {
3266 user_exit();
3267
3268 if (test_thread_flag(TIF_SYSCALL_EMU)) {
> 3269 tracehook_report_syscall_entry(regs);
3270 /*
3271 * Returning -1 will skip the syscall execution. We want to
3272 * avoid clobbering any register also, thus, not 'gotoing'
3273 * skip label.
3274 */
3275 return -1;
3276 }
3277
3278 /*
3279 * The tracer may decide to abort the syscall, if so tracehook
3280 * will return !0. Note that the tracer may also just change
3281 * regs->gpr[0] to an invalid syscall number, that is handled
3282 * below on the exit path.
3283 */
3284 if (test_thread_flag(TIF_SYSCALL_TRACE) &&
3285 tracehook_report_syscall_entry(regs))
3286 goto skip;
3287
3288 /* Run seccomp after ptrace; allow it to set gpr[3]. */
3289 if (do_seccomp(regs))
3290 return -1;
3291
3292 /* Avoid trace and audit when syscall is invalid. */
3293 if (regs->gpr[0] >= NR_syscalls)
3294 goto skip;
3295
3296 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
3297 trace_sys_enter(regs, regs->gpr[0]);
3298

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