Is it OK for trunk or I need to change something?
By the way, I'm seeking a possibility to include this into 12.2. Then
we leaves only 12.1 without this attribute, and we can just say
"building the kernel needs GCC 12.2 or later".
On Mon, 2022-08-01 at 18:07 +0800, Xi Ruoyao wrote:
> Changes v4 -> v5: Fix changelog. No code change.
>
> 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)++;
> +}
--
Xi Ruoyao <xry...@xry111.site>
School of Aerospace Science and Technology, Xidian University
