Re: [Xen-devel] [PATCH 7/7] tools/kdd: mute spurious gcc warning

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Apr 06, 2018 at 09:39:50AM -0400, Boris Ostrovsky wrote:
> On 04/06/2018 09:07 AM, Wei Liu wrote:
> > On Fri, Apr 06, 2018 at 08:39:53AM -0400, Boris Ostrovsky wrote:
> >> On 04/04/2018 09:50 PM, Marek Marczykowski-Górecki wrote:
> >>> gcc-8 complains:
> >>>
> >>>     kdd.c:698:13: error: 'memcpy' offset [-204, -717] is out of the 
> >>> bounds [0, 216] of object 'ctrl' with type 'kdd_ctrl' {aka 'union 
> >>> <anonymous>'} [-Werror=array-bounds]
> >>>                  memcpy(buf, ((uint8_t *)&ctrl.c32) + offset, len);
> >>>                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>>     kdd.c: In function 'kdd_select_callback':
> >>>     kdd.c:642:14: note: 'ctrl' declared here
> >>>          kdd_ctrl ctrl;
> >>>                   ^~~~
> >>>
> >>> But this is impossible - 'offset' is unsigned and correctly validated
> >>> few lines before.
> >>>
> >>> Signed-off-by: Marek Marczykowski-Górecki 
> >>> <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> >>> ---
> >>>  tools/debugger/kdd/kdd.c | 3 +++
> >>>  1 file changed, 3 insertions(+)
> >>>
> >>> diff --git a/tools/debugger/kdd/kdd.c b/tools/debugger/kdd/kdd.c
> >>> index 1bd5dd5..61d769e 100644
> >>> --- a/tools/debugger/kdd/kdd.c
> >>> +++ b/tools/debugger/kdd/kdd.c
> >>> @@ -695,7 +695,10 @@ static void kdd_handle_read_ctrl(kdd_state *s)
> >>>              KDD_LOG(s, "Request outside of known control space\n");
> >>>              len = 0;
> >>>          } else {
> >>> +#pragma GCC diagnostic push
> >>> +#pragma GCC diagnostic ignored "-Warray-bounds"
> >>>              memcpy(buf, ((uint8_t *)&ctrl.c32) + offset, len);
> >>> +#pragma GCC diagnostic pop
> >>>          }
> >>>      }
> >>>  
> >>
> >> Breaks 32-bit build, at least with my (ancient, gcc version 4.4.5
> >> 20101112 (Red Hat 4.4.5-2) (GCC)) compiler:
> >>
> >>
> >>
> >> kdd.c: In function ‘kdd_handle_read_ctrl’:
> >> kdd.c:698: error: #pragma GCC diagnostic not allowed inside functions
> >> kdd.c:699: error: #pragma GCC diagnostic not allowed inside functions
> >> kdd.c:701: error: #pragma GCC diagnostic not allowed inside functions
> >> make[5]: *** [kdd.o] Error 1
> >>
> > Does moving the relevant #pragma's outside of the function fix it?
> 
> The additional problem with these pragmas is that apparently push/pop
> have been introduced in gcc 4.6.0:
> 
> https://gcc.gnu.org/onlinedocs/gcc-4.6.0/gcc/Diagnostic-Pragmas.html#Diagnostic-Pragmas
> 
> If you change release number to a lower one (e.g. 4.5.4) you won't see them.
> 
> So I can move "diagnostic ignored" from inside the function and that
> will clear the "GCC diagnostic not allowed inside functions" error. But
> then push/pop are not recognized:
> 
> cc1: warnings being treated as errors
> kdd.c:639: error: expected [error|warning|ignored] after ‘#pragma GCC
> diagnostic’
> kdd.c:714: error: expected [error|warning|ignored] after ‘#pragma GCC
> diagnostic’
> 
> (Interestingly, my 64-bit build completed without issues)

Hmm... this is messy.

If you have information about which version does what we can try to
enclose the #pragma's with #if __GCC__.

Wei.

> 
> -boris

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