Re: [PATCH v2 2/2] kernel.h: Disable -Wreturn-stack-address for _THIS_IP_

[Nick Desaulniers]

On Tue, Jul 31, 2018 at 10:02 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Tue, Jul 31, 2018 at 9:48 AM, Nick Desaulniers
> > On Tue, Jul 31, 2018 at 3:27 AM kbuild test robot <lkp@xxxxxxxxx> wrote:
> >>    drivers/net//wireless/intel/iwlwifi/iwl-trans.c: In function 'iwl_trans_send_cmd':
> >> >> drivers/net//wireless/intel/iwlwifi/iwl-trans.c:137:2: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
> >>      if (!(cmd->flags & CMD_ASYNC))
> >>      ^~
> >>    drivers/net//wireless/intel/iwlwifi/iwl-trans.c:138:1: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
> >>       lock_map_acquire_read(&trans->sync_cmd_lockdep_map);
> >>     ^ ~
> >>
> >> vim +/if +137 drivers/net//wireless/intel/iwlwifi/iwl-trans.c
> >>
> >> 92fe8343 Emmanuel Grumbach 2015-12-01 @137      if (!(cmd->flags & CMD_ASYNC))
> >> 92fe8343 Emmanuel Grumbach 2015-12-01  138              lock_map_acquire_read(&trans->sync_cmd_lockdep_map);
>
> #define lock_map_acquire_read(l)
> lock_acquire_shared_recursive(l, 0, 0, NULL, _THIS_IP_)
>
> #define lock_acquire_shared_recursive(l, s, t, n, i)
> lock_acquire(l, s, t, 2, 1, n, i)
>
> The config doesn't have CONFIG_LOCKDEP, so it's not:
>
> extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
>                          int trylock, int read, int check,
>                          struct lockdep_map *nest_lock, unsigned long ip);
>
> but rather:
>
> # define lock_acquire(l, s, t, r, c, n, i)      do { } while (0)

This is tricky, if I preprocess that translation unit with the exact
flags used during compilation, I get:

```
 if (!(cmd->flags & CMD_ASYNC))

#pragma GCC diagnostic push

#pragma GCC diagnostic pop
 do { } while (0);
```

Which is not enough to trigger -Wmisleading-indentation alone.  It is
curious that if we add braces to that if statement (as Nathan notes in
a sibling post) or removing the pop (not shippable) seems to fix the
warning.

-- 
Thanks,
~Nick Desaulniers