Mesa (master): st/glsl_to_tgsi: avoid iterating past the head of the instruction list

[Marek Olšák]

Module: Mesa
Branch: master
Commit: 911391bd70fe30ad970c5e56632b2d7ccc29d955
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=911391bd70fe30ad970c5e56632b2d7ccc29d955

Author: Nicolai Hähnle <nicolai.haehnle at amd.com>
Date:   Wed Feb 22 20:04:39 2017 +0100

st/glsl_to_tgsi: avoid iterating past the head of the instruction list

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

Signed-off-by: Marek Olšák <marek.olsak at amd.com>

---

 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 d43d821..af41bdb 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -3611,10 +3611,17 @@ glsl_to_tgsi_visitor::visit_ssbo_intrinsic(ir_call *ir)
       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