Hi, this is Ping #2 for a patch from 2024.
It adds a new target hook that allows to output
assembly code for a VAR_DECL in a custom way.
The default action is an obvious no-op,
i.e. assemble_variable() behaves like before.
This hook is needed in the avr backend to properly implement
some variable attributes. The avr part has already been approved.
The patch is bootstrapped, and it tests without new regressions.
Ok for trunk?
Johann
--
Original submission
https://gcc.gnu.org/pipermail/gcc-patches/2025-January/673459.html
Ping #1
https://gcc.gnu.org/pipermail/gcc-patches/2025-January/673459.html
avr part and approval
https://gcc.gnu.org/pipermail/gcc-patches/2024-December/672051.html
https://gcc.gnu.org/pipermail/gcc-patches/2024-December/672084.html
--
Add new target hook TARGET_ASM_VARIABLE.
This patch adds a new target hook that allows the backend to asm output
a variable definition in its own way. This hook is needed because
varasm.cc imposes a very restrictive layout for all variable definitions
which will be basically ELF style (on ELF targets as least). To date,
there is no way for a backend to output a variable definition in a
different way.
This hook is required by the avr backend when it outputs definitions
for variables defined with the "io", "io_low" or "address" attribute that
don't follow ELF style. These attributes are basically symbol definitions
of the form
.global var_io
var_io = 32
with some additional assertions.
gcc/
* target.def (TARGET_ASM_OUT) <variable>: Add new DEFHOOK.
* targhooks.cc (default_asm_out_variable): New function.
* targhooks.h (default_asm_out_variable): New prototype.
* doc/tm.texi.in (TARGET_ASM_VARIABLE): Place hook documentation.
* doc/tm.texi: Rebuild.
* varasm.cc (assemble_variable): Call targetm.asm_out.variable
in order to allow the backend to output a variable definition
in its own style.
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index d7170f45206..12c09c88e6c 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -8522,6 +8522,24 @@ The default implementation of this hook will use the
when the relevant string is @code{NULL}.
@end deftypefn
+@deftypefn {Target Hook} bool TARGET_ASM_VARIABLE (FILE *@var{stream}, tree @var{decl}, const char *@var{name})
+This hook outputs the assembly code for a @var{decl} that satisfies
+@code{VAR_P} for an object with assembler name @var{name}.
+@code{DECL_RTL (@var{decl})} is of the form @code{(mem (symbol_ref))}.
+Returns @code{true} when the output has been performed and
+@code{false}, otherwise.
+
+It is unlikely that you'll ever neede to implement this hook.
+The middle-and knows how to output object definitions in terms of hook
+macros and functions like @code{GLOBAL_ASM_OP},
+@code{TARGET_ASM_INTEGER}, etc.
+
+When the output is performed by means of this hook, then the complete object
+definition has to be emit, including directives like @code{.global},
+@code{.size}, @code{.type}, @code{.section}, the object label and the
+object content.
+@end deftypefn
+
@deftypefn {Target Hook} void TARGET_ASM_DECL_END (void)
Define this hook if the target assembler requires a special marker to
terminate an initialized variable declaration.
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index f6657f9df1d..2bfeb6ca310 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -5256,6 +5256,8 @@ It must not be modified by command-line option processing.
@hook TARGET_ASM_INTEGER
+@hook TARGET_ASM_VARIABLE
+
@hook TARGET_ASM_DECL_END
@hook TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA
diff --git a/gcc/target.def b/gcc/target.def
index 8cf29c57eae..e90b4bad134 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -93,6 +93,26 @@ when the relevant string is @code{NULL}.",
bool, (rtx x, unsigned int size, int aligned_p),
default_assemble_integer)
+DEFHOOK
+(variable,
+ "This hook outputs the assembly code for a @var{decl} that satisfies\n\
+@code{VAR_P} for an object with assembler name @var{name}.\n\
+@code{DECL_RTL (@var{decl})} is of the form @code{(mem (symbol_ref))}.\n\
+Returns @code{true} when the output has been performed and\n\
+@code{false}, otherwise.\n\
+\n\
+It is unlikely that you'll ever neede to implement this hook.\n\
+The middle-and knows how to output object definitions in terms of hook\n\
+macros and functions like @code{GLOBAL_ASM_OP},\n\
+@code{TARGET_ASM_INTEGER}, etc.\n\
+\n\
+When the output is performed by means of this hook, then the complete object\n\
+definition has to be emit, including directives like @code{.global},\n\
+@code{.size}, @code{.type}, @code{.section}, the object label and the\n\
+object content.",
+ bool, (FILE *stream, tree decl, const char *name),
+ default_asm_out_variable)
+
/* Assembly strings required after the .cfi_startproc label. */
DEFHOOK
(post_cfi_startproc,
diff --git a/gcc/targhooks.cc b/gcc/targhooks.cc
index 8ea8d778003..c0833b4573d 100644
--- a/gcc/targhooks.cc
+++ b/gcc/targhooks.cc
@@ -1463,6 +1463,14 @@ default_asm_out_destructor (rtx symbol ATTRIBUTE_UNUSED,
sorry ("global destructors not supported on this target");
}
+/* The default implementation of TARGET_ASM_VARIABLE doesn't handle decl. */
+
+bool
+default_asm_out_variable (FILE *, tree, const char *)
+{
+ return false;
+}
+
/* By default, do no modification. */
tree default_mangle_decl_assembler_name (tree decl ATTRIBUTE_UNUSED,
tree id)
diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index 7cf22038100..b6e6c1ae267 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -187,6 +187,7 @@ extern int default_reloc_rw_mask (void);
extern bool default_generate_pic_addr_diff_vec (void);
extern void default_asm_out_constructor (rtx, int);
extern void default_asm_out_destructor (rtx, int);
+extern bool default_asm_out_variable (FILE *, tree, const char *);
extern tree default_mangle_decl_assembler_name (tree, tree);
extern tree default_emutls_var_fields (tree, tree *);
extern tree default_emutls_var_init (tree, tree, tree);
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index 0068ec2ce4d..06c54eef6f7 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -2560,6 +2560,12 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
if (TREE_PUBLIC (decl) && DECL_NAME (decl))
notice_global_symbol (decl);
+ if (! dont_output_data)
+ {
+ if (targetm.asm_out.variable (asm_out_file, decl, name))
+ return;
+ }
+
/* Compute the alignment of this data. */
align_variable (decl, dont_output_data);
