[PATCH v6] LoongArch: add addr_global attribute

[Xi Ruoyao <xry111@xry111.site>]

v5 -> v6:

* still use "addr_global" as we don't have a better name.
* add a test case with -mno-explicit-relocs.

-- >8 --

A linker script and/or a section attribute may locate a local object in
some way unexpected by the code model, leading to a link failure.  This
happens when the Linux kernel loads a module with "local" per-CPU
variables.

Add an attribute to explicitly mark an variable with the address
unlimited by the code model so we would be able to work around such
problems.

gcc/ChangeLog:

	* config/loongarch/loongarch.cc (loongarch_attribute_table):
	New attribute table.
	(TARGET_ATTRIBUTE_TABLE): Define the target hook.
	(loongarch_handle_addr_global_attribute): New static function.
	(loongarch_classify_symbol): Return SYMBOL_GOT_DISP for
	SYMBOL_REF_DECL with addr_global attribute.
	(loongarch_use_anchors_for_symbol_p): New static function.
	(TARGET_USE_ANCHORS_FOR_SYMBOL_P): Define the target hook.
	* doc/extend.texi (Variable Attributes): Document new
	LoongArch specific attribute.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/attr-addr_global-1.c: New test.
	* gcc.target/loongarch/attr-addr_global-2.c: New test.
---
 gcc/config/loongarch/loongarch.cc             | 63 +++++++++++++++++++
 gcc/doc/extend.texi                           | 17 +++++
 .../gcc.target/loongarch/attr-addr_global-1.c | 29 +++++++++
 .../gcc.target/loongarch/attr-addr_global-2.c | 29 +++++++++
 4 files changed, 138 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/loongarch/attr-addr_global-1.c
 create mode 100644 gcc/testsuite/gcc.target/loongarch/attr-addr_global-2.c

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 79687340dfd..978e66ed549 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -1643,6 +1643,15 @@ loongarch_classify_symbol (const_rtx x)
       && !loongarch_symbol_binds_local_p (x))
     return SYMBOL_GOT_DISP;
 
+  if (SYMBOL_REF_P (x))
+    {
+      tree decl = SYMBOL_REF_DECL (x);
+      /* An addr_global symbol may be out of the +/- 2GiB range around
+	 the PC, so we have to use GOT.  */
+      if (decl && lookup_attribute ("addr_global", DECL_ATTRIBUTES (decl)))
+	return SYMBOL_GOT_DISP;
+    }
+
   return SYMBOL_PCREL;
 }
 
@@ -6068,6 +6077,54 @@ loongarch_starting_frame_offset (void)
   return crtl->outgoing_args_size;
 }
 
+static tree
+loongarch_handle_addr_global_attribute (tree *node, tree name, tree, int,
+					bool *no_add_attrs)
+{
+  tree decl = *node;
+  if (TREE_CODE (decl) == VAR_DECL)
+    {
+      if (DECL_CONTEXT (decl)
+	  && TREE_CODE (DECL_CONTEXT (decl)) == FUNCTION_DECL
+	  && !TREE_STATIC (decl))
+	{
+	  error_at (DECL_SOURCE_LOCATION (decl),
+		    "%qE attribute cannot be specified for local "
+		    "variables", name);
+	  *no_add_attrs = true;
+	}
+    }
+  else
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      *no_add_attrs = true;
+    }
+  return NULL_TREE;
+}
+
+static const struct attribute_spec loongarch_attribute_table[] =
+{
+  /* { name, min_len, max_len, decl_req, type_req, fn_type_req,
+       affects_type_identity, handler, exclude } */
+  { "addr_global", 0, 0, true, false, false, false,
+    loongarch_handle_addr_global_attribute, NULL },
+  /* The last attribute spec is set to be NULL.  */
+  {}
+};
+
+bool
+loongarch_use_anchors_for_symbol_p (const_rtx symbol)
+{
+  tree decl = SYMBOL_REF_DECL (symbol);
+
+  /* An addr_global attribute indicates the linker may move the symbol away,
+     so the use of anchor may cause relocation overflow.  */
+  if (decl && lookup_attribute ("addr_global", DECL_ATTRIBUTES (decl)))
+    return false;
+
+  return default_use_anchors_for_symbol_p (symbol);
+}
+
 /* Initialize the GCC target structure.  */
 #undef TARGET_ASM_ALIGNED_HI_OP
 #define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"
@@ -6256,6 +6313,12 @@ loongarch_starting_frame_offset (void)
 #undef  TARGET_HAVE_SPECULATION_SAFE_VALUE
 #define TARGET_HAVE_SPECULATION_SAFE_VALUE speculation_safe_value_not_needed
 
+#undef  TARGET_ATTRIBUTE_TABLE
+#define TARGET_ATTRIBUTE_TABLE loongarch_attribute_table
+
+#undef  TARGET_USE_ANCHORS_FOR_SYMBOL_P
+#define TARGET_USE_ANCHORS_FOR_SYMBOL_P loongarch_use_anchors_for_symbol_p
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-loongarch.h"
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 7fe7f8817cd..b1173e15c7c 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -7314,6 +7314,7 @@ attributes.
 * Blackfin Variable Attributes::
 * H8/300 Variable Attributes::
 * IA-64 Variable Attributes::
+* LoongArch Variable Attributes::
 * M32R/D Variable Attributes::
 * MeP Variable Attributes::
 * Microsoft Windows Variable Attributes::
@@ -8098,6 +8099,22 @@ defined by shared libraries.
 
 @end table
 
+@node LoongArch Variable Attributes
+@subsection LoongArch Variable Attributes
+
+One attribute is currently defined for the LoongArch.
+
+@table @code
+@item addr_global
+@cindex @code{addr_global} variable attribute, LoongArch
+Use this attribute on the LoongArch to mark an object possible to be
+located anywhere in the address space by the linker, so its address is
+unlimited by the local data section range specified by the code model even
+if the object is defined locally.  This attribute is mostly useful if a
+@code{section} attribute and/or a linker script will place the object
+somewhere unexpected by the code model.
+@end table
+
 @node M32R/D Variable Attributes
 @subsection M32R/D Variable Attributes
 
diff --git a/gcc/testsuite/gcc.target/loongarch/attr-addr_global-1.c b/gcc/testsuite/gcc.target/loongarch/attr-addr_global-1.c
new file mode 100644
index 00000000000..c1553713d9d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/attr-addr_global-1.c
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-mexplicit-relocs -mcmodel=normal -O2" } */
+/* { dg-final { scan-assembler-not "%pc" } } */
+/* { dg-final { scan-assembler-times "%got_pc_hi20" 3 } } */
+
+/* addr_global attribute should mark x and y possibly outside of the local
+   data range defined by the code model, so GOT should be used instead of
+   PC-relative.  */
+
+int x __attribute__((addr_global));
+int y __attribute__((addr_global));
+
+int
+test(void)
+{
+  return x + y;
+}
+
+/* The following will be used for kernel per-cpu storage implemention. */
+
+register char *per_cpu_base __asm__("r21");
+static int counter __attribute__((section(".data..percpu"), addr_global));
+
+void
+inc_counter(void)
+{
+  int *ptr = (int *)(per_cpu_base + (long)&counter);
+  (*ptr)++;
+}
diff --git a/gcc/testsuite/gcc.target/loongarch/attr-addr_global-2.c b/gcc/testsuite/gcc.target/loongarch/attr-addr_global-2.c
new file mode 100644
index 00000000000..708f163975f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/attr-addr_global-2.c
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-mno-explicit-relocs -mcmodel=normal -O2" } */
+/* { dg-final { scan-assembler-not "la.local" } } */
+/* { dg-final { scan-assembler-times "la.global" 3 } } */
+
+/* addr_global attribute should mark x and y possibly outside of the local
+   data range defined by the code model, so GOT should be used instead of
+   PC-relative.  */
+
+int x __attribute__((addr_global));
+int y __attribute__((addr_global));
+
+int
+test(void)
+{
+  return x + y;
+}
+
+/* The following will be used for kernel per-cpu storage implemention. */
+
+register char *per_cpu_base __asm__("r21");
+static int counter __attribute__((section(".data..percpu"), addr_global));
+
+void
+inc_counter(void)
+{
+  int *ptr = (int *)(per_cpu_base + (long)&counter);
+  (*ptr)++;
+}
-- 
2.37.2