From: Nicolai Hähnle <nicolai.haeh...@amd.com>
Results are undefined but may not crash. Without this change, out-of-bounds
indexing can lead to VM faults and GPU hangs.
Constant buffers, samplers, and possibly others will eventually need similar
treatment to support GL_ARB_robust_buffer_access_behavior.
---
src/gallium/drivers/radeonsi/si_shader.c | 44 +++++++++++++++++++++++++++++++-
1 file changed, 43 insertions(+), 1 deletion(-)
diff --git a/src/gallium/drivers/radeonsi/si_shader.c
b/src/gallium/drivers/radeonsi/si_shader.c
index 9ad2290..1e4bf82 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -532,6 +532,37 @@ static LLVMValueRef get_indirect_index(struct
si_shader_context *ctx,
}
/**
+ * Like get_indirect_index, but restricts the return value to a (possibly
+ * undefined) value inside [0..num).
+ */
+static LLVMValueRef get_bounded_indirect_index(struct si_shader_context *ctx,
+ const struct tgsi_ind_register
*ind,
+ int rel_index, unsigned num)
+{
+ struct gallivm_state *gallivm = &ctx->radeon_bld.gallivm;
+ LLVMBuilderRef builder = gallivm->builder;
+ LLVMValueRef result = get_indirect_index(ctx, ind, rel_index);
+ LLVMValueRef c_max = LLVMConstInt(ctx->i32, num - 1, 0);
+ LLVMValueRef cc;
+
+ if (util_is_power_of_two(num)) {
+ result = LLVMBuildAnd(builder, result, c_max, "");
+ } else {
+ /* In theory, this MAX pattern should result in code that is
+ * as good as the bit-wise AND above.
+ *
+ * In practice, LLVM generates worse code (at the time of
+ * writing), because its value tracking is not strong enough.
+ */
+ cc = LLVMBuildICmp(builder, LLVMIntULE, result, c_max, "");
+ result = LLVMBuildSelect(builder, cc, result, c_max, "");
+ }
+
+ return result;
+}
+
+
+/**
* Calculate a dword address given an input or output register and a stride.
*/
static LLVMValueRef get_dw_address(struct si_shader_context *ctx,
@@ -2814,7 +2845,18 @@ image_fetch_rsrc(
LLVMValueRef rsrc_ptr;
LLVMValueRef tmp;
- ind_index = get_indirect_index(ctx, &image->Indirect,
image->Register.Index);
+ /* From the GL_ARB_shader_image_load_store extension spec:
+ *
+ * If a shader performs an image load, store, or atomic
+ * operation using an image variable declared as an array,
+ * and if the index used to select an individual element is
+ * negative or greater than or equal to the size of the
+ * array, the results of the operation are undefined but may
+ * not lead to termination.
+ */
+ ind_index = get_bounded_indirect_index(ctx, &image->Indirect,
+ image->Register.Index,
+ SI_NUM_IMAGES);
rsrc_ptr = LLVMGetParam(ctx->radeon_bld.main_fn,
SI_PARAM_IMAGES);
tmp = build_indexed_load_const(ctx, rsrc_ptr, ind_index);
--
2.5.0
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