[Mesa-dev] [PATCH] glsl: Fail linkage when UBO exceeds GL_MAX_UNIFORM_BLOCK_SIZE.

Jose Fonseca jfonseca at vmware.com
Tue Jun 16 03:29:13 PDT 2015

It's not totally clear whether other Mesa drivers can safely cope with
over-sized UBOs, but at least for llvmpipe receiving a UBO larger than
its limit causes problems, as it won't fit into its internal display

This fixes piglit "arb_uniform_buffer_object-maxuniformblocksize
fsexceed" without regressions for llvmpipe.

NVIDIA driver also fails to link the shader from
"arb_uniform_buffer_object-maxuniformblocksize fsexceed".

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65525

PS: I don't recommend cherry-picking this for Mesa stable, as some app
might inadvertently been relying on UBOs larger than
GL_MAX_UNIFORM_BLOCK_SIZE to work on other drivers, so even if this
commit is universally accepted it's probably best to let it mature in
master for a while.
 src/glsl/linker.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 9978380..4a726d4 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -2355,6 +2355,13 @@ check_resources(struct gl_context *ctx, struct gl_shader_program *prog)
    unsigned total_uniform_blocks = 0;
    for (unsigned i = 0; i < prog->NumUniformBlocks; i++) {
+      if (prog->UniformBlocks[i].UniformBufferSize > ctx->Const.MaxUniformBlockSize) {
+         linker_error(prog, "Uniform block %s too big (%d/%d)\n",
+                      prog->UniformBlocks[i].Name,
+                      prog->UniformBlocks[i].UniformBufferSize,
+                      ctx->Const.MaxUniformBlockSize);
+      }
       for (unsigned j = 0; j < MESA_SHADER_STAGES; j++) {
 	 if (prog->UniformBlockStageIndex[j][i] != -1) {

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