[Mesa-stable] [PATCH 3/4] st/glsl_to_tgsi: avoid iterating past the head of the instruction list

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

exec_node::get_prev() does not guard against going past the beginning
of the list, so we need to add explicit checks here.

Found by ASAN in piglit arb_shader_storage_buffer_object-rendering.

Cc: mesa-stable at lists.freedesktop.org
---
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index 630f5af..fac41b8 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -3603,24 +3603,31 @@ glsl_to_tgsi_visitor::visit_ssbo_intrinsic(ir_call *ir)
    }
 
    /* The emit_asm() might have actually split the op into pieces, e.g. for
     * double stores. We have to go back and fix up all the generated ops.
     */
    unsigned op = inst->op;
    do {
       inst->resource = buffer;
       if (access)
          inst->buffer_access = access->value.u[0];
+
+      if (inst == this->instructions.get_head_raw())
+         break;
       inst = (glsl_to_tgsi_instruction *)inst->get_prev();
-      if (inst->op == TGSI_OPCODE_UADD)
+
+      if (inst->op == TGSI_OPCODE_UADD) {
+         if (inst == this->instructions.get_head_raw())
+            break;
          inst = (glsl_to_tgsi_instruction *)inst->get_prev();
-   } while (inst && inst->op == op && inst->resource.file == PROGRAM_UNDEFINED);
+      }
+   } while (inst->op == op && inst->resource.file == PROGRAM_UNDEFINED);
 }
 
 void
 glsl_to_tgsi_visitor::visit_membar_intrinsic(ir_call *ir)
 {
    switch (ir->callee->intrinsic_id) {
    case ir_intrinsic_memory_barrier:
       emit_asm(ir, TGSI_OPCODE_MEMBAR, undef_dst,
                st_src_reg_for_int(TGSI_MEMBAR_SHADER_BUFFER |
                                   TGSI_MEMBAR_ATOMIC_BUFFER |
-- 
2.9.3