Re: [Valgrind-developers] -Wcast-qual enabled

[Rhys K. <rhy...@gm...>]

Hi Florian and list,

A short patch to SVN trunk after r14656 is required to compile cleanly on
Darwin. See attached and below for the patch to
coregrind/m_debuginfo/readmacho.c

Regards,
Rhys

Index: coregrind/m_debuginfo/readmacho.c
===================================================================
--- coregrind/m_debuginfo/readmacho.c    (revision 14656)
+++ coregrind/m_debuginfo/readmacho.c    (working copy)
@@ -703,8 +703,8 @@
    Bool     have_uuid    = False;
    UChar    uuid[16];
    Word     i;
-   struct _DebugInfoMapping* rx_map = NULL;
-   struct _DebugInfoMapping* rw_map = NULL;
+   const DebugInfoMapping* rx_map = NULL;
+   const DebugInfoMapping* rw_map = NULL;

    /* mmap the object file to look for di->soname and di->text_bias
       and uuid and nlist */
@@ -715,7 +715,7 @@
    vg_assert(di->fsm.have_rw_map);

    for (i = 0; i < VG_(sizeXA)(di->fsm.maps); i++) {
-      struct _DebugInfoMapping* map = VG_(indexXA)(di->fsm.maps, i);
+      const DebugInfoMapping* map = VG_(indexXA)(di->fsm.maps, i);
       if (map->rx && !rx_map)
          rx_map = map;
       if (map->rw && !rw_map)



On 22 October 2014 23:55, Florian Krohm <fl...@ei...> wrote:

> Greetings.
>
> I've just enabled the -Wcast-qual option for compilation of the
> valgrind code base. Testcases are not compiled with -Wcast-qual as
> that is not very interesting.
> I've tested this:
> - on s390x with GCC 3.4.6 and 4.8.3
> - on ppc64be with GCC 4.7.2
> - on amd64 with GCC 4.8.2, clang 3.0 and clang 3.5.0
>
> I would appreciate if somebody with access to Darwin, ARM and MIPS
> platforms could give it a spin.
>
> For the curious, there are some spots in the code where a cast that
> drops a type qualifier is unavoidable. For instance:
>
> HChar* VG_(strchr) ( const HChar* s, HChar c )
> {
>    while (True) {
>       if (*s == c) return (HChar *)s;
>       if (*s == 0) return NULL;
>       s++;
>    }
> }
>
> To get this compiled with -Wcast-qual and have no warnings there are
> basically two options.
> One is to enclose such offensive code with
>
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wcast-qual"
>
> HChar* VG_(strchr) .......
>
> #pragma GCC diagnostic pop
>
> The other option is to replace the cast with some type punning trickery:
>
> #define CONST_CAST(T,x)    \
>    ({                      \
>       union {              \
>          const T in;      \
>          T out;           \
>       } var = { .in = x }; var.out;  \
>    })
>
> and use it like so:
>
>     if (*s == c) return CONST_CAST(HChar *,s);
>
> I opted for the latter as it is less intrusive. The construct is
> guaranteed to work even with -fstrict-aliasing (which we're not using).
>
> Also, C99 says (6.5.2.3, footnote 82):
> If the member used to access the contents of a union object is not the
> same as the member last used to store a value in the object, the
> appropriate part of the object representation of the value is
> reinterpreted as an object representation in the new type.
>
> Which is exactly what is being done in that macro.
>
>    Florian
>
>
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