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[PATCH] Add generic support for "noinit" attribute


Hi,

Similar to what already exists for TI msp430 or in TI compilers for
arm, this patch adds support for the "noinit" attribute.

It is convenient for embedded targets where the user wants to keep the
value of some data when the program is restarted: such variables are
not zero-initialized. It is mostly a helper/shortcut to placing
variables in a dedicated section.

It's probably desirable to add the following chunk to the GNU linker:
diff --git a/ld/emulparams/armelf.sh b/ld/emulparams/armelf.sh
index 272a8bc..9555cec 100644
--- a/ld/emulparams/armelf.sh
+++ b/ld/emulparams/armelf.sh
@@ -10,7 +10,19 @@ OTHER_TEXT_SECTIONS='*(.glue_7t) *(.glue_7)
*(.vfp11_veneer) *(.v4_bx)'
 OTHER_BSS_SYMBOLS="${CREATE_SHLIB+PROVIDE (}__bss_start__ =
.${CREATE_SHLIB+)};"
 OTHER_BSS_END_SYMBOLS="${CREATE_SHLIB+PROVIDE (}_bss_end__ =
.${CREATE_SHLIB+)}; ${CREATE_SHLIB+PROVIDE (}__bss_end__ =
.${CREATE_SHLIB+)};"
 OTHER_END_SYMBOLS="${CREATE_SHLIB+PROVIDE (}__end__ = .${CREATE_SHLIB+)};"
 -OTHER_SECTIONS='.note.gnu.arm.ident 0 : { KEEP (*(.note.gnu.arm.ident)) }'
 +OTHER_SECTIONS='
 +.note.gnu.arm.ident 0 : { KEEP (*(.note.gnu.arm.ident)) }
 +  /* This section contains data that is not initialised during load
 +     *or* application reset.  */
 +   .noinit (NOLOAD) :
 +   {
 +     . = ALIGN(2);
 +     PROVIDE (__noinit_start = .);
 +     *(.noinit)
 +     . = ALIGN(2);
 +     PROVIDE (__noinit_end = .);
 +   }
 +'

so that the noinit section has the "NOLOAD" flag.

I'll submit that part separately to the binutils project if OK.

However, I'm not sure for which other targets (beyond arm), I should
update the linker scripts.

I left the new testcase in gcc.target/arm, guarded by
dg-do run { target { *-*-eabi } }
but since this attribute is now generic, I suspect I should move the
test to some other place. But then, which target selector should I
use?

Finally, I tested on arm-eabi, but not on msp430 for which I do not
have the environment, so advice from msp430 maintainers is
appreciated. Since msp430 does not use the same default helpers as
arm, I left the "noinit" handling code in place, to avoid changing
other generic functions which I don't know how to test
(default_select_section, default_section_type_flags).

Thanks,

Christophe

gcc/ChangeLog:

2019-07-04  Christophe Lyon  <christophe.lyon@linaro.org>

* doc/extend.texi: Add "noinit" attribute documentation.
* varasm.c
(default_section_type_flags): Add support for "noinit" section.
(default_elf_select_section): Add support for "noinit" attribute.

gcc/c-family/ChangeLog:

2019-07-04  Christophe Lyon  <christophe.lyon@linaro.org>

* c-attribs.c (c_common_attribute_table): Add "noinit" entry.
(handle_section_attribute): Add support for "noinit" attribute.
(handle_noinit_attribute): New function.

gcc/config/ChangeLog:

2019-07-04  Christophe Lyon  <christophe.lyon@linaro.org>

* msp430/msp430.c (msp430_attribute_table): Remove "noinit" entry.

gcc/testsuite/ChangeLog:

2019-07-04  Christophe Lyon  <christophe.lyon@linaro.org>

* gcc.target/arm/noinit-attribute.c: New test.

Attachment: noinit-generic.patch.txt
Description: Text document


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