[systemd-devel] [PATCH] util: fix strict aliasing violations in use of struct inotify_event

[Lennart Poettering]

On Mon, 22.12.14 00:17, Shawn Paul Landden (shawn at churchofgit.com) wrote:

> There is alot of cleanup that will have to happen to turn on
> -fstrict-aliasing, but I think our code should be "correct" to the
> rule.

I don#t think -fstrict-aliasing can really work given that we use some
rather broken APIs from other libraries that are not compatible with
the idea.

That said, I think the inotify thing is something we really could fix,
so the patch is something we should merge. But before that, can you
fix one thing: please define the union in the header file, somwhere
next to where we define INOTIFY_EVENT_MAX? Maybe call it "union
inotify_event_buffer" or so, and then use it everywhere?

Thanks!

> ---
>  src/journal/sd-journal.c | 9 ++++++---
>  src/shared/util.c        | 9 ++++++---
>  src/udev/udevd.c         | 9 ++++++---
>  3 files changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c
> index d46dc3c..fb4cd85 100644
> --- a/src/journal/sd-journal.c
> +++ b/src/journal/sd-journal.c
> @@ -2188,11 +2188,14 @@ _public_ int sd_journal_process(sd_journal *j) {
>          j->last_process_usec = now(CLOCK_MONOTONIC);
>  
>          for (;;) {
> -                uint8_t buffer[INOTIFY_EVENT_MAX] _alignas_(struct inotify_event);
> +                union {
> +                        struct inotify_event ev;
> +                        uint8_t raw[INOTIFY_EVENT_MAX];
> +                } buffer;
>                  struct inotify_event *e;
>                  ssize_t l;
>  
> -                l = read(j->inotify_fd, buffer, sizeof(buffer));
> +                l = read(j->inotify_fd, buffer.raw, sizeof(buffer.raw));
>                  if (l < 0) {
>                          if (errno == EAGAIN || errno == EINTR)
>                                  return got_something ? determine_change(j) : SD_JOURNAL_NOP;
> @@ -2202,7 +2205,7 @@ _public_ int sd_journal_process(sd_journal *j) {
>  
>                  got_something = true;
>  
> -                FOREACH_INOTIFY_EVENT(e, buffer, l)
> +                FOREACH_INOTIFY_EVENT(e, &buffer.ev, l)
>                          process_inotify_event(j, e);
>          }
>  }
> diff --git a/src/shared/util.c b/src/shared/util.c
> index 06b6077..13f6f52 100644
> --- a/src/shared/util.c
> +++ b/src/shared/util.c
> @@ -2106,7 +2106,10 @@ int acquire_terminal(
>                  assert(notify >= 0);
>  
>                  for (;;) {
> -                        uint8_t buffer[INOTIFY_EVENT_MAX] _alignas_(struct inotify_event);
> +                        union {
> +                                struct inotify_event ev;
> +                                uint8_t raw[INOTIFY_EVENT_MAX];
> +                        } buffer;
>                          struct inotify_event *e;
>                          ssize_t l;
>  
> @@ -2129,7 +2132,7 @@ int acquire_terminal(
>                                  }
>                          }
>  
> -                        l = read(notify, buffer, sizeof(buffer));
> +                        l = read(notify, buffer.raw, sizeof(buffer.raw));
>                          if (l < 0) {
>                                  if (errno == EINTR || errno == EAGAIN)
>                                          continue;
> @@ -2138,7 +2141,7 @@ int acquire_terminal(
>                                  goto fail;
>                          }
>  
> -                        FOREACH_INOTIFY_EVENT(e, buffer, l) {
> +                        FOREACH_INOTIFY_EVENT(e, &buffer.ev, l) {
>                                  if (e->wd != wd || !(e->mask & IN_CLOSE)) {
>                                          r = -EIO;
>                                          goto fail;
> diff --git a/src/udev/udevd.c b/src/udev/udevd.c
> index 8bec03e..98ddd67 100644
> --- a/src/udev/udevd.c
> +++ b/src/udev/udevd.c
> @@ -816,11 +816,14 @@ static int synthesize_change(struct udev_device *dev) {
>  }
>  
>  static int handle_inotify(struct udev *udev) {
> -        uint8_t buffer[INOTIFY_EVENT_MAX] _alignas_(struct inotify_event);
> +        union {
> +                struct inotify_event ev;
> +                uint8_t raw[INOTIFY_EVENT_MAX];
> +        } buffer;
>          struct inotify_event *e;
>          ssize_t l;
>  
> -        l = read(fd_inotify, buffer, sizeof(buffer));
> +        l = read(fd_inotify, buffer.raw, sizeof(buffer.raw));
>          if (l < 0) {
>                  if (errno == EAGAIN || errno == EINTR)
>                          return 0;
> @@ -828,7 +831,7 @@ static int handle_inotify(struct udev *udev) {
>                  return log_error_errno(errno, "Failed to read inotify fd: %m");
>          }
>  
> -        FOREACH_INOTIFY_EVENT(e, buffer, l) {
> +        FOREACH_INOTIFY_EVENT(e, &buffer.ev, l) {
>                  struct udev_device *dev;
>  
>                  dev = udev_watch_lookup(udev, e->wd);
> -- 
> 2.1.0
> 
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Lennart

-- 
Lennart Poettering, Red Hat