asan: Fix missing FakeStack flag cleanup

The FakeStack flag is not zeroed out when can_store_by_pieces()
returns false.  Over time, this causes FakeStack::Allocate() to perform
the maximum number of loop iterations, significantly slowing down the
instrumented program.

Link: https://inbox.sourceware.org/gcc-patches/20250109001702.154685-1-iii@linux.ibm.com/
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
gcc/ChangeLog:

	* asan.cc (asan_emit_stack_protection): Always zero the flag
	unless it is cleared by the __asan_stack_free_N() libcall.

diff --git a/gcc/asan.cc b/gcc/asan.cc
index 452a5a333277fae69d2dc54663b51e79148929a1..ebf806cffb64556a10091e492c8723d58584d749 100644 (file)
--- a/gcc/asan.cc
+++ b/gcc/asan.cc
@@ -2167,28 +2167,13 @@ asan_emit_stack_protection (rtx base, rtx pbase, unsigned int alignb,
       mem = adjust_address (mem, VOIDmode, base_align_bias);
       emit_move_insn (mem, gen_int_mode (ASAN_STACK_RETIRED_MAGIC, ptr_mode));
       unsigned HOST_WIDE_INT sz = asan_frame_size >> ASAN_SHADOW_SHIFT;
+      bool asan_stack_free_emitted_p = false;
       if (use_after_return_class < 5
          && can_store_by_pieces (sz, builtin_memset_read_str, &c,
                                  BITS_PER_UNIT, true))
-       {
-         /* Emit:
-              memset(ShadowBase, kAsanStackAfterReturnMagic, ShadowSize);
-              **SavedFlagPtr(FakeStack, class_id) = 0
-         */
-         store_by_pieces (shadow_mem, sz, builtin_memset_read_str, &c,
-                          BITS_PER_UNIT, true, RETURN_BEGIN);
-
-         unsigned HOST_WIDE_INT offset
-           = (1 << (use_after_return_class + 6));
-         offset -= GET_MODE_SIZE (ptr_mode);
-         mem = gen_rtx_MEM (ptr_mode, base);
-         mem = adjust_address (mem, ptr_mode, offset);
-         rtx addr = gen_reg_rtx (ptr_mode);
-         emit_move_insn (addr, mem);
-         addr = convert_memory_address (Pmode, addr);
-         mem = gen_rtx_MEM (QImode, addr);
-         emit_move_insn (mem, const0_rtx);
-       }
+       /* Emit memset (ShadowBase, kAsanStackAfterReturnMagic, ShadowSize).  */
+       store_by_pieces (shadow_mem, sz, builtin_memset_read_str, &c,
+                        BITS_PER_UNIT, true, RETURN_BEGIN);
       else if (use_after_return_class >= 5
               || !set_storage_via_setmem (shadow_mem,
                                           GEN_INT (sz),
@@ -2205,6 +2190,20 @@ asan_emit_stack_protection (rtx base, rtx pbase, unsigned int alignb,
                             GEN_INT (asan_frame_size + base_align_bias),
                             TYPE_MODE (pointer_sized_int_node),
                             orig_addr, ptr_mode);
+         asan_stack_free_emitted_p = true;
+       }
+      if (!asan_stack_free_emitted_p)
+       {
+         /* Emit **SavedFlagPtr (FakeStack, class_id) = 0.  */
+         unsigned HOST_WIDE_INT offset = (1 << (use_after_return_class + 6));
+         offset -= GET_MODE_SIZE (ptr_mode);
+         mem = gen_rtx_MEM (ptr_mode, base);
+         mem = adjust_address (mem, ptr_mode, offset);
+         rtx addr = gen_reg_rtx (ptr_mode);
+         emit_move_insn (addr, mem);
+         addr = convert_memory_address (Pmode, addr);
+         mem = gen_rtx_MEM (QImode, addr);
+         emit_move_insn (mem, const0_rtx);
        }
       lab = gen_label_rtx ();
       emit_jump (lab);