[Mesa-dev] [PATCH] gallivm: fix small but severe bug in handling multiple lod level strides

[Jose Fonseca]

----- Original Message -----
> From: Roland Scheidegger <sroland at vmware.com>
> 
> Inserting the value for the second quad in the wrong place for the
> following shuffle. This meant the row or image stride was undefined which is
> quite catastrophic, can lead to bogus texels fetched or just segfault.
> This code is only hit for SoA path currently, still surprising it
> didn't crash more or caused more visible issues (I think llvm used a
> broadcast shuffle for the undefined parts of the vector, hence the undefined
> value for the second quad was just the same as that from the first quad,
> so as long as both quads hit the same mip level everything was fine, and
> since
> lower mips always have the same large stride it made it less likely to
> hit out-of-bound memory in case of differing lods).
> 
> Note: this is a candidate for release branches.
> ---
>  src/gallium/auxiliary/gallivm/lp_bld_sample.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample.c
> b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
> index 7f44c4e..f885363 100644
> --- a/src/gallium/auxiliary/gallivm/lp_bld_sample.c
> +++ b/src/gallium/auxiliary/gallivm/lp_bld_sample.c
> @@ -934,7 +934,7 @@ lp_build_get_level_stride_vec(struct
> lp_build_sample_context *bld,
>        stride = bld->int_coord_bld.undef;
>        for (i = 0; i < bld->num_lods; i++) {
>           LLVMValueRef indexi = lp_build_const_int32(bld->gallivm, i);
> -         LLVMValueRef indexo = lp_build_const_int32(bld->gallivm, i);
> +         LLVMValueRef indexo = lp_build_const_int32(bld->gallivm, 4 * i);
>           indexes[1] = LLVMBuildExtractElement(builder, level, indexi, "");
>           stride1 = LLVMBuildGEP(builder, stride_array, indexes, 2, "");
>           stride1 = LLVMBuildLoad(builder, stride1, "");
> --
> 1.7.9.5
> 


 
Reviewed-by: Jose Fonseca <jfonseca at vmware.com>