exec: Build page-vary-common.c with -fno-lto

In bbc17caf81f, we used an alias attribute to allow target_page
to be declared const, and yet be initialized late.

This fails when using LTO with several versions of gcc.
The compiler looks through the alias and decides that the const
variable is statically initialized to zero, then propagates that
zero to many uses of the variable.

This can be avoided by compiling one object file with -fno-lto.
In this way, any initializer cannot be seen, and the constant
propagation does not occur.

Since we are certain to have this separate compilation unit, we
can drop the alias attribute as well.  We simply have differing
declarations for target_page in different compilation units.
Drop the use of init_target_page, and drop the configure detection
for CONFIG_ATTRIBUTE_ALIAS.

In order to change the compilation flags for a file with meson,
we must use a static_library.  This runs into specific_ss, where
we would need to create many static_library instances.

Fix this by splitting page-vary.c: the page-vary-common.c part is
compiled once as a static_library, while the page-vary.c part is
left in specific_ss in order to handle the target-specific value
of TARGET_PAGE_BITS_MIN.

Reported-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210321211534.2101231-1-richard.henderson@linaro.org>
[PMD: Fix typo in subject, split original patch in 3]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Gavin Shan <gshan@redhat.com>
Message-Id: <20210322112427.4045204-4-f4bug@amsat.org>
[rth: Update MAINTAINERS]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/page-vary-common.c b/page-vary-common.c
new file mode 100644
index 0000000000..9175556498
--- /dev/null
+++ b/page-vary-common.c
@@ -0,0 +1,54 @@
+/*
+ * Variable page size handling -- target independent part.
+ *
+ *  Copyright (c) 2003 Fabrice Bellard
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define IN_PAGE_VARY 1
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "exec/page-vary.h"
+
+/* WARNING: This file must *not* be complied with -flto. */
+
+TargetPageBits target_page;
+
+bool set_preferred_target_page_bits_common(int bits)
+{
+    /*
+     * The target page size is the lowest common denominator for all
+     * the CPUs in the system, so we can only make it smaller, never
+     * larger. And we can't make it smaller once we've committed to
+     * a particular size.
+     */
+    if (target_page.bits == 0 || target_page.bits > bits) {
+        if (target_page.decided) {
+            return false;
+        }
+        target_page.bits = bits;
+    }
+    return true;
+}
+
+void finalize_target_page_bits_common(int min)
+{
+    if (target_page.bits == 0) {
+        target_page.bits = min;
+    }
+    target_page.mask = -1ull << target_page.bits;
+    target_page.decided = true;
+}