[lttng-dev] [PATCH lttng-ust] Fix: ustfork: save and restore errno in syscall wrappers

[Mathieu Desnoyers]

Merged into master, 2.10, 2.9, thanks!

Mathieu

----- On Mar 5, 2018, at 4:09 PM, Michael Jeanson mjeanson at efficios.com wrote:

> Signed-off-by: Michael Jeanson <mjeanson at efficios.com>
> ---
> liblttng-ust-fork/ustfork.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
> 
> diff --git a/liblttng-ust-fork/ustfork.c b/liblttng-ust-fork/ustfork.c
> index 43b8d8f..71c4b86 100644
> --- a/liblttng-ust-fork/ustfork.c
> +++ b/liblttng-ust-fork/ustfork.c
> @@ -33,6 +33,7 @@ pid_t fork(void)
> 	static pid_t (*plibc_func)(void) = NULL;
> 	sigset_t sigset;
> 	pid_t retval;
> +	int saved_errno;
> 
> 	if (plibc_func == NULL) {
> 		plibc_func = dlsym(RTLD_NEXT, "fork");
> @@ -46,12 +47,14 @@ pid_t fork(void)
> 	ust_before_fork(&sigset);
> 	/* Do the real fork */
> 	retval = plibc_func();
> +	saved_errno = errno;
> 	if (retval == 0) {
> 		/* child */
> 		ust_after_fork_child(&sigset);
> 	} else {
> 		ust_after_fork_parent(&sigset);
> 	}
> +	errno = saved_errno;
> 	return retval;
> }
> 
> @@ -60,6 +63,7 @@ int daemon(int nochdir, int noclose)
> 	static int (*plibc_func)(int nochdir, int noclose) = NULL;
> 	sigset_t sigset;
> 	int retval;
> +	int saved_errno;
> 
> 	if (plibc_func == NULL) {
> 		plibc_func = dlsym(RTLD_NEXT, "daemon");
> @@ -73,6 +77,7 @@ int daemon(int nochdir, int noclose)
> 	ust_before_fork(&sigset);
> 	/* Do the real daemon call */
> 	retval = plibc_func(nochdir, noclose);
> +	saved_errno = errno;
> 	if (retval == 0) {
> 		/* child, parent called _exit() directly */
> 		ust_after_fork_child(&sigset);
> @@ -80,6 +85,7 @@ int daemon(int nochdir, int noclose)
> 		/* on error in the parent */
> 		ust_after_fork_parent(&sigset);
> 	}
> +	errno = saved_errno;
> 	return retval;
> }
> 
> @@ -114,6 +120,7 @@ int clone(int (*fn)(void *), void *child_stack, int flags,
> void *arg, ...)
> 	/* end of var args */
> 	va_list ap;
> 	int retval;
> +	int saved_errno;
> 
> 	va_start(ap, arg);
> 	ptid = va_arg(ap, pid_t *);
> @@ -137,6 +144,7 @@ int clone(int (*fn)(void *), void *child_stack, int flags,
> void *arg, ...)
> 		 */
> 		retval = plibc_func(fn, child_stack, flags, arg, ptid,
> 				tls, ctid);
> +		saved_errno = errno;
> 	} else {
> 		/* Creating a real process, we need to intervene. */
> 		struct ustfork_clone_info info = { .fn = fn, .arg = arg };
> @@ -144,9 +152,11 @@ int clone(int (*fn)(void *), void *child_stack, int flags,
> void *arg, ...)
> 		ust_before_fork(&info.sigset);
> 		retval = plibc_func(clone_fn, child_stack, flags, &info,
> 				ptid, tls, ctid);
> +		saved_errno = errno;
> 		/* The child doesn't get here. */
> 		ust_after_fork_parent(&info.sigset);
> 	}
> +	errno = saved_errno;
> 	return retval;
> }
> 
> @@ -157,6 +167,7 @@ pid_t rfork(int flags)
> 	static pid_t (*plibc_func)(void) = NULL;
> 	sigset_t sigset;
> 	pid_t retval;
> +	int saved_errno;
> 
> 	if (plibc_func == NULL) {
> 		plibc_func = dlsym(RTLD_NEXT, "rfork");
> @@ -170,12 +181,14 @@ pid_t rfork(int flags)
> 	ust_before_fork(&sigset);
> 	/* Do the real rfork */
> 	retval = plibc_func();
> +	saved_errno = errno;
> 	if (retval == 0) {
> 		/* child */
> 		ust_after_fork_child(&sigset);
> 	} else {
> 		ust_after_fork_parent(&sigset);
> 	}
> +	errno = saved_errno;
> 	return retval;
> }
> 
> --
> 2.7.4

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com