[PATCH v4] LoongArch: add movable attribute

[Xi Ruoyao <xry111@xry111.site>]

Changes v3 -> v4:

 * Use "movable" as the attribute name as Huacai says it's already used
   in downstream GCC fork.
 * Remove an inaccurate line from the doc. (Initially I tried to
   implement a "model(...)" like IA64 or M32R. Then I changed my mind
   but forgot to remove the line copied from M32R doc.)

-- >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/addr-global.c: New test.
---
 gcc/config/loongarch/loongarch.cc | 63 +++++++++++++++++++
 gcc/doc/extend.texi | 16 +++++
 .../gcc.target/loongarch/attr-movable.c | 29 +++++++++
 3 files changed, 108 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/loongarch/attr-movable.c

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 79687340dfd..6b6026700a6 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);
+ /* A movable symbol may be moved away from the +/- 2GiB range around
+ the PC, so we have to use GOT. */
+ if (decl && lookup_attribute ("movable", 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_movable_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 } */
+ { "movable", 0, 0, true, false, false, false,
+ loongarch_handle_movable_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);
+
+ /* A movable attribute indicates the linker may move the symbol away,
+ so the use of anchor may cause relocation overflow. */
+ if (decl && lookup_attribute ("movable", 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..322d8c05a04 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 +8099,21 @@ 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 movable
+@cindex @code{movable} variable attribute, LoongArch
+Use this attribute on the LoongArch to mark an object possible to be moved
+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 move 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-movable.c b/gcc/testsuite/gcc.target/loongarch/attr-movable.c
new file mode 100644
index 00000000000..85b1dd4c59a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/attr-movable.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 } } */
+
+/* movable 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__((movable));
+int y __attribute__((movable));
+
+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"), movable));
+
+void
+inc_counter(void)
+{
+ int *ptr = (int *)(per_cpu_base + (long)&counter);
+ (*ptr)++;
+}
-- 
2.37.1