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virgl: Fix a strict-aliasing violation in the encoder

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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 double
to uint64_t interpretations of the memory.

V.2: Use static_assert() instead of assert().
V.3: Use C99 compat STATIC_ASSERT() over C11 static_assert().

Signed-off-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Acked-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Edward O'Callaghan 2016-12-06 10:43:17 +11:00
parent 35c5a9a64d
commit 5e6b2b05a5
1 changed files with 7 additions and 1 deletions
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8
src/gallium/drivers/virgl/virgl_encode.c
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@ -21,6 +21,8 @@
* USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include <stdint.h>
#include <assert.h>
#include <string.h>
#include "util/u_format.h"
#include "util/u_memory.h"
@ -315,12 +317,16 @@ int virgl_encode_clear(struct virgl_context *ctx,
double depth, unsigned stencil)
{
int i;
uint64_t qword;
STATIC_ASSERT(sizeof(qword) == sizeof(depth));
memcpy(&qword, &depth, sizeof(qword));
virgl_encoder_write_cmd_dword(ctx, VIRGL_CMD0(VIRGL_CCMD_CLEAR, 0, VIRGL_OBJ_CLEAR_SIZE));
virgl_encoder_write_dword(ctx->cbuf, buffers);
for (i = 0; i < 4; i++)
virgl_encoder_write_dword(ctx->cbuf, color->ui[i]);
virgl_encoder_write_qword(ctx->cbuf, *(uint64_t *)&depth);
virgl_encoder_write_qword(ctx->cbuf, qword);
virgl_encoder_write_dword(ctx->cbuf, stencil);
return 0;
}