[Mesa-dev] [PATCH v3 2/3] svga: Fix a strict-aliasing violation in shader dumper

[Edward O'Callaghan]

Brian/Roland ping?

On 12/07/2016 10:30 AM, Edward O'Callaghan wrote:
> As per the C spec, it is illegal to alias pointers to different
> types. This results in undefined behaviour after optimization
> passes, resulting in very subtle bugs that happen only on a
> full moon..
> 
> Use a memcpy() as a well defined coercion between the isomorphic
> bit-field interpretations of memory.
> 
> V.2: Use C99 compat STATIC_ASSERT() over C11 static_assert().
> 
> Signed-off-by: Edward O'Callaghan <funfunctor at folklore1984.net>
> ---
>  src/gallium/drivers/svga/svgadump/svga_shader_dump.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/src/gallium/drivers/svga/svgadump/svga_shader_dump.c b/src/gallium/drivers/svga/svgadump/svga_shader_dump.c
> index 4ee1bf2..46126a5 100644
> --- a/src/gallium/drivers/svga/svgadump/svga_shader_dump.c
> +++ b/src/gallium/drivers/svga/svgadump/svga_shader_dump.c
> @@ -30,6 +30,9 @@
>   * @author Michal Krol <michal at vmware.com>
>   */
>  
> +#include <assert.h>
> +#include <string.h>
> +
>  #include "svga_shader.h"
>  #include "svga_shader_dump.h"
>  #include "svga_shader_op.h"
> @@ -413,6 +416,11 @@ dump_dstreg(struct sh_dstreg dstreg,
>  
>  static void dump_srcreg( struct sh_srcreg srcreg, struct sh_srcreg *indreg, const struct dump_info *di )
>  {
> +   struct sh_reg srcreg_sh = {0};
> +   /* bit-fields carefully aligned, ensure they stay that way. */
> +   STATIC_ASSERT(sizeof(struct sh_reg) == sizeof(struct sh_srcreg));
> +   memcpy(&srcreg_sh, &srcreg, sizeof(srcreg_sh));
> +
>     switch (srcreg.modifier) {
>     case SVGA3DSRCMOD_NEG:
>     case SVGA3DSRCMOD_BIASNEG:
> @@ -427,7 +435,7 @@ static void dump_srcreg( struct sh_srcreg srcreg, struct sh_srcreg *indreg, cons
>     case SVGA3DSRCMOD_NOT:
>        _debug_printf( "!" );
>     }
> -   dump_reg( *(struct sh_reg *) &srcreg, indreg, di );
> +   dump_reg(srcreg_sh, indreg, di );
>     switch (srcreg.modifier) {
>     case SVGA3DSRCMOD_NONE:
>     case SVGA3DSRCMOD_NEG:
> 

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