Sorry for the slow response, I'd missed that there was an updated patch...
Christophe Lyon <christophe.l...@linaro.org> writes:
> 2019-07-04 Christophe Lyon <christophe.l...@linaro.org>
>
> * lib/target-supports.exp (check_effective_target_noinit): New
> proc.
> * gcc.c-torture/execute/noinit-attribute.c: New test.
Second line should be indented by tabs rather than spaces.
> @@ -2224,6 +2234,54 @@ handle_weak_attribute (tree *node, tree name,
> return NULL_TREE;
> }
>
> +/* Handle a "noinit" attribute; arguments as in struct
> + attribute_spec.handler. Check whether the attribute is allowed
> + here and add the attribute to the variable decl tree or otherwise
> + issue a diagnostic. This function checks NODE is of the expected
> + type and issues diagnostics otherwise using NAME. If it is not of
> + the expected type *NO_ADD_ATTRS will be set to true. */
> +
> +static tree
> +handle_noinit_attribute (tree * node,
> + tree name,
> + tree args,
> + int flags ATTRIBUTE_UNUSED,
> + bool *no_add_attrs)
> +{
> + const char *message = NULL;
> +
> + gcc_assert (DECL_P (*node));
> + gcc_assert (args == NULL);
> +
> + if (TREE_CODE (*node) != VAR_DECL)
> + message = G_("%qE attribute only applies to variables");
> +
> + /* Check that it's possible for the variable to have a section. */
> + else if ((TREE_STATIC (*node) || DECL_EXTERNAL (*node) || in_lto_p)
> + && DECL_SECTION_NAME (*node))
> + message = G_("%qE attribute cannot be applied to variables "
> + "with specific sections");
> +
> + if (!targetm.have_switchable_bss_sections)
> + message = G_("%qE attribute is specific to ELF targets");
Maybe make this an else if too? Or make the VAR_DECL an else if
if you think the ELF one should win. Either way, it seems odd to
have the mixture between else if and not.
> + if (message)
> + {
> + warning (OPT_Wattributes, message, name);
> + *no_add_attrs = true;
> + }
> + else
> + /* If this var is thought to be common, then change this. Common
> + variables are assigned to sections before the backend has a
> + chance to process them. Do this only if the attribute is
> + valid. */
Comment should be indented two spaces more.
> + if (DECL_COMMON (*node))
> + DECL_COMMON (*node) = 0;
> +
> + return NULL_TREE;
> +}
> +
> +
> /* Handle a "noplt" attribute; arguments as in
> struct attribute_spec.handler. */
>
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index f2619e1..f1af1dc 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -7129,6 +7129,14 @@ The @code{visibility} attribute is described in
> The @code{weak} attribute is described in
> @ref{Common Function Attributes}.
>
> +@item noinit
> +@cindex @code{noinit} variable attribute
> +Any data with the @code{noinit} attribute will not be initialized by
> +the C runtime startup code, or the program loader. Not initializing
> +data in this way can reduce program startup times. Specific to ELF
> +targets, this attribute relies on the linker to place such data in the
> +right location.
Maybe:
This attribute is specific to ELF targets and relies on the linker to
place such data in the right location.
> diff --git a/gcc/testsuite/gcc.c-torture/execute/noinit-attribute.c
> b/gcc/testsuite/gcc.c-torture/execute/noinit-attribute.c
> new file mode 100644
> index 0000000..ffcf8c6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/noinit-attribute.c
> @@ -0,0 +1,59 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target noinit */
> +/* { dg-options "-O2" } */
> +
> +/* This test checks that noinit data is handled correctly. */
> +
> +extern void _start (void) __attribute__ ((noreturn));
> +extern void abort (void) __attribute__ ((noreturn));
> +extern void exit (int) __attribute__ ((noreturn));
> +
> +int var_common;
> +int var_zero = 0;
> +int var_one = 1;
> +int __attribute__((noinit)) var_noinit;
> +int var_init = 2;
> +
> +int __attribute__((noinit)) func(); /* { dg-warning "attribute only applies
> to variables" } */
> +int __attribute__((section ("mysection"), noinit)) var_section1; /* {
> dg-warning "because it conflicts with attribute" } */
> +int __attribute__((noinit, section ("mysection"))) var_section2; /* {
> dg-warning "because it conflicts with attribute" } */
> +
> +
> +int
> +main (void)
> +{
> + /* Make sure that the C startup code has correctly initialized the
> ordinary variables. */
> + if (var_common != 0)
> + abort ();
> +
> + /* Initialized variables are not re-initialized during startup, so
> + check their original values only during the first run of this
> + test. */
> + if (var_init == 2)
> + if (var_zero != 0 || var_one != 1)
> + abort ();
> +
> + switch (var_init)
> + {
> + case 2:
> + /* First time through - change all the values. */
> + var_common = var_zero = var_one = var_noinit = var_init = 3;
> + break;
> +
> + case 3:
> + /* Second time through - make sure that d has not been reset. */
> + if (var_noinit != 3)
> + abort ();
> + exit (0);
> +
> + default:
> + /* Any other value for var_init is an error. */
> + abort ();
> + }
> +
> + /* Simulate a processor reset by calling the C startup code. */
> + _start ();
> +
> + /* Should never reach here. */
> + abort ();
> +}
> diff --git a/gcc/testsuite/lib/target-supports.exp
> b/gcc/testsuite/lib/target-supports.exp
> index 815e837..ae05c0a 100644
> --- a/gcc/testsuite/lib/target-supports.exp
> +++ b/gcc/testsuite/lib/target-supports.exp
> @@ -364,6 +364,18 @@ proc check_weak_override_available { } {
> return [check_weak_available]
> }
>
> +# The noinit attribute is only supported by some targets.
> +# This proc returns 1 if it's supported, 0 if it's not.
> +
> +proc check_effective_target_noinit { } {
> + if { [istarget arm*-*-eabi]
> + || [istarget msp430-*-*] } {
> + return 1
> + }
> +
> + return 0
> +}
> +
> ###############################
> # proc check_visibility_available { what_kind }
> ###############################
> diff --git a/gcc/varasm.c b/gcc/varasm.c
> index 626a4c9..6ddab0ce 100644
> --- a/gcc/varasm.c
> +++ b/gcc/varasm.c
> @@ -6428,6 +6428,9 @@ default_section_type_flags (tree decl, const char
> *name, int reloc)
> || strncmp (name, ".gnu.linkonce.tb.", 17) == 0)
> flags |= SECTION_TLS | SECTION_BSS;
>
> + if (strcmp (name, ".noinit") == 0)
> + flags |= SECTION_WRITE | SECTION_BSS | SECTION_NOTYPE;
> +
> /* Various sections have special ELF types that the assembler will
> assign by default based on the name. They are neither SHT_PROGBITS
> nor SHT_NOBITS, so when changing sections we don't want to print a
> @@ -6748,11 +6751,14 @@ decl_readonly_section (const_tree decl, int reloc)
>
> /* Select a section based on the above categorization. */
>
> +static section *noinit_section = NULL;
> +
No longer needed.
OK with those changes, thanks.
Richard
> section *
> default_elf_select_section (tree decl, int reloc,
> unsigned HOST_WIDE_INT align)
> {
> const char *sname;
> +
> switch (categorize_decl_for_section (decl, reloc))
> {
> case SECCAT_TEXT:
> @@ -6790,6 +6796,13 @@ default_elf_select_section (tree decl, int reloc,
> sname = ".tdata";
> break;
> case SECCAT_BSS:
> + if (DECL_P (decl)
> + && lookup_attribute ("noinit", DECL_ATTRIBUTES (decl)) != NULL_TREE)
> + {
> + sname = ".noinit";
> + break;
> + }
> +
> if (bss_section)
> return bss_section;
> sname = ".bss";
