Early exit in es2::Context::drawElements on count=0.

This fixes an issue where es2::Context::drawElements would still try to read draw data even when there are 0 elements to draw, causing a buffer overflow on draw data. This was found by running Android ES3 dEQP under ASAN. The failing tests are EQP-GLES3.functional.primitive_restart.[begin_restart, begin_restart_duplicate_restarts, begin_restart_end_restart, begin_restart_end_restart_duplicate_restarts, end_restart_duplicate_restarts, duplicate_restarts].* The crashing dEQP tests cover glDrawElementsInstanced, glDrawRangeElements, and glDrawElements. These all converge onto es2::Context::drawElements. Bug: b/123716871 Change-Id: I4bca0616eb9f92bf18a3331459f3dcd06b8ac9a9 Signed-off-by: Cody Schuffelen <schuffelen@google.com> Test: cts-tradefed run commandAndExit cts -m CtsDeqpTestCases --module-arg 'CtsDeqpTestCases:include-filter:dEQP-GLES3.functional.primitive_restart.*' Reviewed-on: https://swiftshader-review.googlesource.com/c/24548 Kokoro-Presubmit: kokoro <noreply+kokoro@google.com> Reviewed-by: Nicolas Capens <nicolascapens@google.com>

Early exit in es2::Context::drawElements on count=0.
96861534 · Cody Schuffelen · 7fb0b73b · 96861534
Commit 96861534 authored Feb 07, 2019 by Cody Schuffelen
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Context.cpp src/OpenGL/libGLESv2/Context.cpp +5 -0

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--- a/src/OpenGL/libGLESv2/Context.cpp
+++ b/src/OpenGL/libGLESv2/Context.cpp
@@ -3628,6 +3628,11 @@ void Context::drawElements(GLenum mode, GLuint start, GLuint end, GLsizei count,
 		return;   // Nothing to process.
 	}
+	if(count == 0)
+	{
+		return;
+	}
 	if(!indices && !getCurrentVertexArray()->getElementArrayBuffer())
 	{
 		return error(GL_INVALID_OPERATION);