Re: V3 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Wed, 2 Dec 2020, H.J. Lu via Gcc-patches wrote: > > Not sure if this is a GCC bug or indicates that glibc's libc_freeres_fn or > > related macros need to change to work with both old and new GCC. > > We may need to update glibc for GCC 11. Can you open a glibc bug and > CC me? https://sourceware.org/bugzilla/show_bug.cgi?id=27002 -- Joseph S. Myers jos...@codesourcery.com
Re: V3 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Wed, Dec 2, 2020 at 1:31 PM Joseph Myers wrote: > > This patch (GCC commit 6fbec038f7a7ddf29f074943611b53210d17c40c) has > broken the glibc build (at least with current binutils master). The > errors are of the form: > > In file included from : > gconv_dl.c: In function 'free_mem': > gconv_dl.c:202:18: error: 'free_mem' causes a section type conflict with > 'do_release_all' > 202 | libc_freeres_fn (free_mem) > | ^~~~ > ./../include/libc-symbols.h:316:15: note: in definition of macro > 'libc_freeres_fn' > 316 | static void name (void) > | ^~~~ > gconv_dl.c:191:1: note: 'do_release_all' was declared here > 191 | do_release_all (void *nodep) > | ^~ > > Not sure if this is a GCC bug or indicates that glibc's libc_freeres_fn or > related macros need to change to work with both old and new GCC. We may need to update glibc for GCC 11. Can you open a glibc bug and CC me? Thanks. -- H.J.
Re: V3 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
This patch (GCC commit 6fbec038f7a7ddf29f074943611b53210d17c40c) has broken the glibc build (at least with current binutils master). The errors are of the form: In file included from : gconv_dl.c: In function 'free_mem': gconv_dl.c:202:18: error: 'free_mem' causes a section type conflict with 'do_release_all' 202 | libc_freeres_fn (free_mem) | ^~~~ ./../include/libc-symbols.h:316:15: note: in definition of macro 'libc_freeres_fn' 316 | static void name (void) | ^~~~ gconv_dl.c:191:1: note: 'do_release_all' was declared here 191 | do_release_all (void *nodep) | ^~ Not sure if this is a GCC bug or indicates that glibc's libc_freeres_fn or related macros need to change to work with both old and new GCC. -- Joseph S. Myers jos...@codesourcery.com
Re: V3 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On 12/1/20 5:36 PM, H.J. Lu wrote:
> On Tue, Dec 1, 2020 at 4:04 PM Jeff Law wrote:
>>
>>
>> On 11/17/20 6:20 AM, H.J. Lu via Gcc-patches wrote:
>>> On Mon, Nov 16, 2020 at 7:59 PM Hans-Peter Nilsson
>>> wrote:
>>>> On Fri, 13 Nov 2020, H.J. Lu via Gcc-patches wrote:
>>>>> Done. Here is the updated patch.
>>>> Hi. I see a test-case for this kind of construct:
>>>>
>>>> int foo __attribute__((__used__, __section__ (".bar"))) = 42;
>>>>
>>>> and IIUC that it's handled as I'd hope (setting "R" on the named
>>>> section, not another derived section), good.
>>>>
>>>> Could you also add a test-case that the same construct
>>>> *without* a specific initializer is handled the same way?
>>>> I.e.:
>>>> int foo __attribute__((__used__, __section__ (".bar")));
>>>>
>>> Done. The only changes are
>>>
>>> /* { dg-final { scan-assembler ".data.used_bar_sec,\"awR\"" } } */
>>> ...
>>> int __attribute__((used,section(".data.used_bar_sec"))) used_bar;
>>>
>>> and 2 additional tests for -fcommon.
>>>
>>> Thanks.
>>>
>>>
>>> 0001-Use-SHF_GNU_RETAIN-to-preserve-symbol-definitions.patch
>>>
>>> From d19f2e2ec7f0f47121a2a4c05ffe20af8972c1bb Mon Sep 17 00:00:00 2001
>>> From: "H.J. Lu"
>>> Date: Mon, 3 Feb 2020 11:55:43 -0800
>>> Subject: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
>>>
>>> In assemly code, the section flag 'R' sets the SHF_GNU_RETAIN flag to
>>> indicate that the section must be preserved by the linker.
>>>
>>> Add SECTION_RETAIN to indicate a section should be retained by the linker
>>> and set SECTION_RETAIN on section for the preserved symbol if assembler
>>> supports SHF_GNU_RETAIN. All retained symbols are placed in separate
>>> sections with
>>>
>>> .section .data.rel.local.preserved_symbol,"awR"
>>> preserved_symbol:
>>> ...
>>> .section .data.rel.local,"aw"
>>> not_preserved_symbol:
>>> ...
>>>
>>> to avoid
>>>
>>> .section .data.rel.local,"awR"
>>> preserved_symbol:
>>> ...
>>> not_preserved_symbol:
>>> ...
>>>
>>> which places not_preserved_symbol definition in the SHF_GNU_RETAIN
>>> section.
>>>
>>> gcc/
>>>
>>> 2020-11-XX H.J. Lu
>>>
>>> * configure.ac (HAVE_GAS_SHF_GNU_RETAIN): New. Define 1 if
>>> the assembler supports marking sections with SHF_GNU_RETAIN flag.
>>> * output.h (SECTION_RETAIN): New. Defined as 0x400.
>>> (SECTION_MACH_DEP): Changed from 0x400 to 0x800.
>>> (default_unique_section): Add a bool argument.
>>> * varasm.c (get_section): Set SECTION_RETAIN for the preserved
>>> symbol with HAVE_GAS_SHF_GNU_RETAIN.
>>> (resolve_unique_section): Used named section for the preserved
>>> symbol if assembler supports SHF_GNU_RETAIN.
>>> (get_variable_section): Handle the preserved common symbol with
>>> HAVE_GAS_SHF_GNU_RETAIN.
>>> (default_elf_asm_named_section): Require the full declaration and
>>> use the 'R' flag for SECTION_RETAIN.
>>> * config.in: Regenerated.
>>> * configure: Likewise.
>>>
>>> gcc/testsuite/
>>>
>>> 2020-11-XX H.J. Lu
>>> Jozef Lawrynowicz
>>>
>>> * c-c++-common/attr-used.c: Check the 'R' flag.
>>> * c-c++-common/attr-used-2.c: Likewise.
>>> * c-c++-common/attr-used-3.c: New test.
>>> * c-c++-common/attr-used-4.c: Likewise.
>>> * gcc.c-torture/compile/attr-used-retain-1.c: Likewise.
>>> * gcc.c-torture/compile/attr-used-retain-2.c: Likewise.
>>> * gcc.c-torture/compile/attr-used-retain-3.c: Likewise.
>>> * gcc.c-torture/compile/attr-used-retain-4.c: Likewise.
>>> * lib/target-supports.exp
>>> (check_effective_target_R_flag_in_section): New proc.
>> Can we try to avoid the #if stuff, particulary in varasm.c. We worked
>> pretty hard to reduce the amount of conditionally compiled code through
>> the years and we should try to avoid adding new instances.
>>
>> HAVE_GAS_SHF_GNU_RETAIN is going to be a compile-time c
V3 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Tue, Dec 1, 2020 at 4:04 PM Jeff Law wrote:
>
>
>
> On 11/17/20 6:20 AM, H.J. Lu via Gcc-patches wrote:
> > On Mon, Nov 16, 2020 at 7:59 PM Hans-Peter Nilsson
> > wrote:
> >> On Fri, 13 Nov 2020, H.J. Lu via Gcc-patches wrote:
> >>> Done. Here is the updated patch.
> >> Hi. I see a test-case for this kind of construct:
> >>
> >> int foo __attribute__((__used__, __section__ (".bar"))) = 42;
> >>
> >> and IIUC that it's handled as I'd hope (setting "R" on the named
> >> section, not another derived section), good.
> >>
> >> Could you also add a test-case that the same construct
> >> *without* a specific initializer is handled the same way?
> >> I.e.:
> >> int foo __attribute__((__used__, __section__ (".bar")));
> >>
> > Done. The only changes are
> >
> > /* { dg-final { scan-assembler ".data.used_bar_sec,\"awR\"" } } */
> > ...
> > int __attribute__((used,section(".data.used_bar_sec"))) used_bar;
> >
> > and 2 additional tests for -fcommon.
> >
> > Thanks.
> >
> >
> > 0001-Use-SHF_GNU_RETAIN-to-preserve-symbol-definitions.patch
> >
> > From d19f2e2ec7f0f47121a2a4c05ffe20af8972c1bb Mon Sep 17 00:00:00 2001
> > From: "H.J. Lu"
> > Date: Mon, 3 Feb 2020 11:55:43 -0800
> > Subject: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
> >
> > In assemly code, the section flag 'R' sets the SHF_GNU_RETAIN flag to
> > indicate that the section must be preserved by the linker.
> >
> > Add SECTION_RETAIN to indicate a section should be retained by the linker
> > and set SECTION_RETAIN on section for the preserved symbol if assembler
> > supports SHF_GNU_RETAIN. All retained symbols are placed in separate
> > sections with
> >
> > .section .data.rel.local.preserved_symbol,"awR"
> > preserved_symbol:
> > ...
> > .section .data.rel.local,"aw"
> > not_preserved_symbol:
> > ...
> >
> > to avoid
> >
> > .section .data.rel.local,"awR"
> > preserved_symbol:
> > ...
> > not_preserved_symbol:
> > ...
> >
> > which places not_preserved_symbol definition in the SHF_GNU_RETAIN
> > section.
> >
> > gcc/
> >
> > 2020-11-XX H.J. Lu
> >
> > * configure.ac (HAVE_GAS_SHF_GNU_RETAIN): New. Define 1 if
> > the assembler supports marking sections with SHF_GNU_RETAIN flag.
> > * output.h (SECTION_RETAIN): New. Defined as 0x400.
> > (SECTION_MACH_DEP): Changed from 0x400 to 0x800.
> > (default_unique_section): Add a bool argument.
> > * varasm.c (get_section): Set SECTION_RETAIN for the preserved
> > symbol with HAVE_GAS_SHF_GNU_RETAIN.
> > (resolve_unique_section): Used named section for the preserved
> > symbol if assembler supports SHF_GNU_RETAIN.
> > (get_variable_section): Handle the preserved common symbol with
> > HAVE_GAS_SHF_GNU_RETAIN.
> > (default_elf_asm_named_section): Require the full declaration and
> > use the 'R' flag for SECTION_RETAIN.
> > * config.in: Regenerated.
> > * configure: Likewise.
> >
> > gcc/testsuite/
> >
> > 2020-11-XX H.J. Lu
> > Jozef Lawrynowicz
> >
> > * c-c++-common/attr-used.c: Check the 'R' flag.
> > * c-c++-common/attr-used-2.c: Likewise.
> > * c-c++-common/attr-used-3.c: New test.
> > * c-c++-common/attr-used-4.c: Likewise.
> > * gcc.c-torture/compile/attr-used-retain-1.c: Likewise.
> > * gcc.c-torture/compile/attr-used-retain-2.c: Likewise.
> > * gcc.c-torture/compile/attr-used-retain-3.c: Likewise.
> > * gcc.c-torture/compile/attr-used-retain-4.c: Likewise.
> > * lib/target-supports.exp
> > (check_effective_target_R_flag_in_section): New proc.
> Can we try to avoid the #if stuff, particulary in varasm.c. We worked
> pretty hard to reduce the amount of conditionally compiled code through
> the years and we should try to avoid adding new instances.
>
> HAVE_GAS_SHF_GNU_RETAIN is going to be a compile-time constant, so it
> should be just as efficient to do things like
>
> if (HAVE_GAS_SHF_GNU_RETAIN)
>... whatever ...
Fixed.
> This has the advantage that the same code is presented to the
> front-ends, so we're at lot less likely to stumble over set-but-not-used
> warnings and the like that were so problematical a few years back.
Re: V2 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On 11/17/20 6:20 AM, H.J. Lu via Gcc-patches wrote:
> On Mon, Nov 16, 2020 at 7:59 PM Hans-Peter Nilsson wrote:
>> On Fri, 13 Nov 2020, H.J. Lu via Gcc-patches wrote:
>>> Done. Here is the updated patch.
>> Hi. I see a test-case for this kind of construct:
>>
>> int foo __attribute__((__used__, __section__ (".bar"))) = 42;
>>
>> and IIUC that it's handled as I'd hope (setting "R" on the named
>> section, not another derived section), good.
>>
>> Could you also add a test-case that the same construct
>> *without* a specific initializer is handled the same way?
>> I.e.:
>> int foo __attribute__((__used__, __section__ (".bar")));
>>
> Done. The only changes are
>
> /* { dg-final { scan-assembler ".data.used_bar_sec,\"awR\"" } } */
> ...
> int __attribute__((used,section(".data.used_bar_sec"))) used_bar;
>
> and 2 additional tests for -fcommon.
>
> Thanks.
>
>
> 0001-Use-SHF_GNU_RETAIN-to-preserve-symbol-definitions.patch
>
> From d19f2e2ec7f0f47121a2a4c05ffe20af8972c1bb Mon Sep 17 00:00:00 2001
> From: "H.J. Lu"
> Date: Mon, 3 Feb 2020 11:55:43 -0800
> Subject: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
>
> In assemly code, the section flag 'R' sets the SHF_GNU_RETAIN flag to
> indicate that the section must be preserved by the linker.
>
> Add SECTION_RETAIN to indicate a section should be retained by the linker
> and set SECTION_RETAIN on section for the preserved symbol if assembler
> supports SHF_GNU_RETAIN. All retained symbols are placed in separate
> sections with
>
> .section .data.rel.local.preserved_symbol,"awR"
> preserved_symbol:
> ...
> .section .data.rel.local,"aw"
> not_preserved_symbol:
> ...
>
> to avoid
>
> .section .data.rel.local,"awR"
> preserved_symbol:
> ...
> not_preserved_symbol:
> ...
>
> which places not_preserved_symbol definition in the SHF_GNU_RETAIN
> section.
>
> gcc/
>
> 2020-11-XX H.J. Lu
>
> * configure.ac (HAVE_GAS_SHF_GNU_RETAIN): New. Define 1 if
> the assembler supports marking sections with SHF_GNU_RETAIN flag.
> * output.h (SECTION_RETAIN): New. Defined as 0x400.
> (SECTION_MACH_DEP): Changed from 0x400 to 0x800.
> (default_unique_section): Add a bool argument.
> * varasm.c (get_section): Set SECTION_RETAIN for the preserved
> symbol with HAVE_GAS_SHF_GNU_RETAIN.
> (resolve_unique_section): Used named section for the preserved
> symbol if assembler supports SHF_GNU_RETAIN.
> (get_variable_section): Handle the preserved common symbol with
> HAVE_GAS_SHF_GNU_RETAIN.
> (default_elf_asm_named_section): Require the full declaration and
> use the 'R' flag for SECTION_RETAIN.
> * config.in: Regenerated.
> * configure: Likewise.
>
> gcc/testsuite/
>
> 2020-11-XX H.J. Lu
> Jozef Lawrynowicz
>
> * c-c++-common/attr-used.c: Check the 'R' flag.
> * c-c++-common/attr-used-2.c: Likewise.
> * c-c++-common/attr-used-3.c: New test.
> * c-c++-common/attr-used-4.c: Likewise.
> * gcc.c-torture/compile/attr-used-retain-1.c: Likewise.
> * gcc.c-torture/compile/attr-used-retain-2.c: Likewise.
> * gcc.c-torture/compile/attr-used-retain-3.c: Likewise.
> * gcc.c-torture/compile/attr-used-retain-4.c: Likewise.
> * lib/target-supports.exp
> (check_effective_target_R_flag_in_section): New proc.
Can we try to avoid the #if stuff, particulary in varasm.c. We worked
pretty hard to reduce the amount of conditionally compiled code through
the years and we should try to avoid adding new instances.
HAVE_GAS_SHF_GNU_RETAIN is going to be a compile-time constant, so it
should be just as efficient to do things like
if (HAVE_GAS_SHF_GNU_RETAIN)
... whatever ...
This has the advantage that the same code is presented to the
front-ends, so we're at lot less likely to stumble over set-but-not-used
warnings and the like that were so problematical a few years back. In
fact, you use that style elsewhere in varasm.c :-)
I think you need to document the new effective target check in
doc/sourcebuild.texi
With those changes this should be fine.
jeff
Re: V2 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Mon, Nov 16, 2020 at 7:59 PM Hans-Peter Nilsson wrote:
>
> On Fri, 13 Nov 2020, H.J. Lu via Gcc-patches wrote:
> > Done. Here is the updated patch.
>
> Hi. I see a test-case for this kind of construct:
>
> int foo __attribute__((__used__, __section__ (".bar"))) = 42;
>
> and IIUC that it's handled as I'd hope (setting "R" on the named
> section, not another derived section), good.
>
> Could you also add a test-case that the same construct
> *without* a specific initializer is handled the same way?
> I.e.:
> int foo __attribute__((__used__, __section__ (".bar")));
>
Done. The only changes are
/* { dg-final { scan-assembler ".data.used_bar_sec,\"awR\"" } } */
...
int __attribute__((used,section(".data.used_bar_sec"))) used_bar;
and 2 additional tests for -fcommon.
Thanks.
--
H.J.
From d19f2e2ec7f0f47121a2a4c05ffe20af8972c1bb Mon Sep 17 00:00:00 2001
From: "H.J. Lu"
Date: Mon, 3 Feb 2020 11:55:43 -0800
Subject: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
In assemly code, the section flag 'R' sets the SHF_GNU_RETAIN flag to
indicate that the section must be preserved by the linker.
Add SECTION_RETAIN to indicate a section should be retained by the linker
and set SECTION_RETAIN on section for the preserved symbol if assembler
supports SHF_GNU_RETAIN. All retained symbols are placed in separate
sections with
.section .data.rel.local.preserved_symbol,"awR"
preserved_symbol:
...
.section .data.rel.local,"aw"
not_preserved_symbol:
...
to avoid
.section .data.rel.local,"awR"
preserved_symbol:
...
not_preserved_symbol:
...
which places not_preserved_symbol definition in the SHF_GNU_RETAIN
section.
gcc/
2020-11-XX H.J. Lu
* configure.ac (HAVE_GAS_SHF_GNU_RETAIN): New. Define 1 if
the assembler supports marking sections with SHF_GNU_RETAIN flag.
* output.h (SECTION_RETAIN): New. Defined as 0x400.
(SECTION_MACH_DEP): Changed from 0x400 to 0x800.
(default_unique_section): Add a bool argument.
* varasm.c (get_section): Set SECTION_RETAIN for the preserved
symbol with HAVE_GAS_SHF_GNU_RETAIN.
(resolve_unique_section): Used named section for the preserved
symbol if assembler supports SHF_GNU_RETAIN.
(get_variable_section): Handle the preserved common symbol with
HAVE_GAS_SHF_GNU_RETAIN.
(default_elf_asm_named_section): Require the full declaration and
use the 'R' flag for SECTION_RETAIN.
* config.in: Regenerated.
* configure: Likewise.
gcc/testsuite/
2020-11-XX H.J. Lu
Jozef Lawrynowicz
* c-c++-common/attr-used.c: Check the 'R' flag.
* c-c++-common/attr-used-2.c: Likewise.
* c-c++-common/attr-used-3.c: New test.
* c-c++-common/attr-used-4.c: Likewise.
* gcc.c-torture/compile/attr-used-retain-1.c: Likewise.
* gcc.c-torture/compile/attr-used-retain-2.c: Likewise.
* gcc.c-torture/compile/attr-used-retain-3.c: Likewise.
* gcc.c-torture/compile/attr-used-retain-4.c: Likewise.
* lib/target-supports.exp
(check_effective_target_R_flag_in_section): New proc.
---
gcc/config.in | 7 +++
gcc/configure | 51 +++
gcc/configure.ac | 20
gcc/output.h | 6 ++-
gcc/testsuite/c-c++-common/attr-used-2.c | 1 +
gcc/testsuite/c-c++-common/attr-used-3.c | 7 +++
gcc/testsuite/c-c++-common/attr-used-4.c | 7 +++
gcc/testsuite/c-c++-common/attr-used.c| 1 +
.../compile/attr-used-retain-1.c | 37 ++
.../compile/attr-used-retain-2.c | 17 +++
.../compile/attr-used-retain-3.c | 17 +++
.../compile/attr-used-retain-4.c | 17 +++
gcc/testsuite/lib/target-supports.exp | 40 +++
gcc/varasm.c | 17 +--
14 files changed, 241 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/c-c++-common/attr-used-3.c
create mode 100644 gcc/testsuite/c-c++-common/attr-used-4.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-3.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-4.c
diff --git a/gcc/config.in b/gcc/config.in
index b7c3107bfe3..23ae2f9bc1b 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -1352,6 +1352,13 @@
#endif
+/* Define 0/1 if your assembler supports marking sections with SHF_GNU_RETAIN
+ flag. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_SHF_GNU_RETAIN
+#endif
+
+
/* Define 0/1 if your assembler supports marking sections with SHF_MERGE flag.
*/
#ifndef USED_FOR_TARGET
diff --git a/gcc/configure b/gcc/configure
index dbda4415a17..a925a6e5efb 100755
--- a/gcc/configure
+
Re: V2 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Fri, 13 Nov 2020, H.J. Lu via Gcc-patches wrote:
> Done. Here is the updated patch.
Hi. I see a test-case for this kind of construct:
int foo __attribute__((__used__, __section__ (".bar"))) = 42;
and IIUC that it's handled as I'd hope (setting "R" on the named
section, not another derived section), good.
Could you also add a test-case that the same construct
*without* a specific initializer is handled the same way?
I.e.:
int foo __attribute__((__used__, __section__ (".bar")));
Thanks in advance.
brgds, H-P
V2 [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Fri, Nov 13, 2020 at 3:36 AM Jozef Lawrynowicz wrote: > > On Thu, Nov 12, 2020 at 02:41:52PM -0800, H.J. Lu wrote: > > diff --git a/gcc/varasm.c b/gcc/varasm.c > > index 435c7b348a5..c48ef9692ee 100644 > > --- a/gcc/varasm.c > > +++ b/gcc/varasm.c > > @@ -289,6 +289,10 @@ get_section (const char *name, unsigned int flags, > > tree decl, > >slot = section_htab->find_slot_with_hash (name, htab_hash_string (name), > > INSERT); > >flags |= SECTION_NAMED; > > +#if HAVE_GAS_SHF_GNU_RETAIN > > + if (decl != nullptr && DECL_PRESERVE_P (decl)) > > Minor nit, but I think this should be "decl != NULL_TREE". We are using C++ now. Should we start using nullptr instead of NULL_TREE or NULL_RTX? > We should also test that "used" with the "section" attribute applies the > "R" flag. Please apply the attached patch if this gets approved. These > new tests pass with arm-none-eabi and x86_64-pc-linux-gnu. > Done. Here is the updated patch. -- H.J. From 07c4c78c43d3b94e56d6ace97b660c69998011e4 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Mon, 3 Feb 2020 11:55:43 -0800 Subject: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions In assemly code, the section flag 'R' sets the SHF_GNU_RETAIN flag to indicate that the section must be preserved by the linker. Add SECTION_RETAIN to indicate a section should be retained by the linker and set SECTION_RETAIN on section for the preserved symbol if assembler supports SHF_GNU_RETAIN. All retained symbols are placed in separate sections with .section .data.rel.local.preserved_symbol,"awR" preserved_symbol: ... .section .data.rel.local,"aw" not_preserved_symbol: ... to avoid .section .data.rel.local,"awR" preserved_symbol: ... not_preserved_symbol: ... which places not_preserved_symbol definition in the SHF_GNU_RETAIN section. gcc/ 2020-11-XX H.J. Lu * configure.ac (HAVE_GAS_SHF_GNU_RETAIN): New. Define 1 if the assembler supports marking sections with SHF_GNU_RETAIN flag. * output.h (SECTION_RETAIN): New. Defined as 0x400. (SECTION_MACH_DEP): Changed from 0x400 to 0x800. (default_unique_section): Add a bool argument. * varasm.c (get_section): Set SECTION_RETAIN for the preserved symbol with HAVE_GAS_SHF_GNU_RETAIN. (resolve_unique_section): Used named section for the preserved symbol if assembler supports SHF_GNU_RETAIN. (get_variable_section): Handle the preserved common symbol with HAVE_GAS_SHF_GNU_RETAIN. (default_elf_asm_named_section): Require the full declaration and use the 'R' flag for SECTION_RETAIN. * config.in: Regenerated. * configure: Likewise. gcc/testsuite/ 2020-11-XX H.J. Lu Jozef Lawrynowicz * c-c++-common/attr-used.c: Check the 'R' flag. * c-c++-common/attr-used-2.c: Likewise. * c-c++-common/attr-used-3.c: New test. * c-c++-common/attr-used-4.c: Likewise. * gcc.c-torture/compile/attr-used-retain-1.c: Likewise. * gcc.c-torture/compile/attr-used-retain-2.c: Likewise. * lib/target-supports.exp (check_effective_target_R_flag_in_section): New proc. --- gcc/config.in | 7 +++ gcc/configure | 51 +++ gcc/configure.ac | 20 gcc/output.h | 6 ++- gcc/testsuite/c-c++-common/attr-used-2.c | 1 + gcc/testsuite/c-c++-common/attr-used-3.c | 7 +++ gcc/testsuite/c-c++-common/attr-used-4.c | 7 +++ gcc/testsuite/c-c++-common/attr-used.c| 1 + .../compile/attr-used-retain-1.c | 35 + .../compile/attr-used-retain-2.c | 16 ++ gcc/testsuite/lib/target-supports.exp | 40 +++ gcc/varasm.c | 17 +-- 12 files changed, 204 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/c-c++-common/attr-used-3.c create mode 100644 gcc/testsuite/c-c++-common/attr-used-4.c create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c diff --git a/gcc/config.in b/gcc/config.in index b7c3107bfe3..23ae2f9bc1b 100644 --- a/gcc/config.in +++ b/gcc/config.in @@ -1352,6 +1352,13 @@ #endif +/* Define 0/1 if your assembler supports marking sections with SHF_GNU_RETAIN + flag. */ +#ifndef USED_FOR_TARGET +#undef HAVE_GAS_SHF_GNU_RETAIN +#endif + + /* Define 0/1 if your assembler supports marking sections with SHF_MERGE flag. */ #ifndef USED_FOR_TARGET diff --git a/gcc/configure b/gcc/configure index dbda4415a17..a925a6e5efb 100755 --- a/gcc/configure +++ b/gcc/configure @@ -24272,6 +24272,57 @@ cat >>confdefs.h <<_ACEOF _ACEOF +# Test if the assembler supports the section flag 'R' f
Re: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
On Thu, Nov 12, 2020 at 02:41:52PM -0800, H.J. Lu wrote:
> diff --git a/gcc/varasm.c b/gcc/varasm.c
> index 435c7b348a5..c48ef9692ee 100644
> --- a/gcc/varasm.c
> +++ b/gcc/varasm.c
> @@ -289,6 +289,10 @@ get_section (const char *name, unsigned int flags, tree
> decl,
>slot = section_htab->find_slot_with_hash (name, htab_hash_string (name),
> INSERT);
>flags |= SECTION_NAMED;
> +#if HAVE_GAS_SHF_GNU_RETAIN
> + if (decl != nullptr && DECL_PRESERVE_P (decl))
Minor nit, but I think this should be "decl != NULL_TREE".
We should also test that "used" with the "section" attribute applies the
"R" flag. Please apply the attached patch if this gets approved. These
new tests pass with arm-none-eabi and x86_64-pc-linux-gnu.
Thanks,
Jozef
commit cf8e26deb43d13268ab6ee231995aecbf41ba3a3
Author: Jozef Lawrynowicz
Date: Fri Nov 13 11:07:14 2020 +
Test "used" attribute in conjunction "section" attribute
diff --git a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
index b7763af11e4..5f6cbca6e33 100644
--- a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
+++ b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
@@ -4,6 +4,7 @@
/* { dg-final { scan-assembler ".bss.*,\"awR\"" } } */
/* { dg-final { scan-assembler ".data.*,\"awR\"" } } */
/* { dg-final { scan-assembler ".rodata.*,\"aR\"" } } */
+/* { dg-final { scan-assembler ".data.used_foo_sec,\"awR\"" } } */
void __attribute__((used)) used_fn (void) { }
void unused_fn (void) { }
@@ -30,3 +31,5 @@ int __attribute__((used)) used_data2 = 1;
const int __attribute__((used)) used_rodata2 = 2;
int __attribute__((used)) used_comm2;
static int __attribute__((used)) used_lcomm2;
+
+int __attribute__((used,section(".data.used_foo_sec"))) used_foo = 2;
diff --git a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
index e3b3cf184f8..be5f3917ac8 100644
--- a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
+++ b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
@@ -10,6 +10,7 @@
/* { dg-final { scan-assembler ".rodata.used_rodata2,\"aR\"" } } */
/* { dg-final { scan-assembler ".bss.used_lcomm,\"awR\"" { target arm-*-* } }
} */
/* { dg-final { scan-assembler ".bss.used_lcomm2,\"awR\"" { target arm-*-* } }
} */
+/* { dg-final { scan-assembler ".data.used_foo_sec,\"awR\"" } } */
/* { dg-options "-ffunction-sections -fdata-sections" } */
#include "attr-used-retain-1.c"
[PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions
In assemly code, the section flag 'R' sets the SHF_GNU_RETAIN flag to
indicate that the section must be preserved by the linker.
Add SECTION_RETAIN to indicate a section should be retained by the linker
and set SECTION_RETAIN on section for the preserved symbol if assembler
supports SHF_GNU_RETAIN. All retained symbols are placed in separate
sections with
.section .data.rel.local.preserved_symbol,"awR"
preserved_symbol:
...
.section .data.rel.local,"aw"
not_preserved_symbol:
...
to avoid
.section .data.rel.local,"awR"
preserved_symbol:
...
not_preserved_symbol:
...
which places not_preserved_symbol definition in the SHF_GNU_RETAIN
section.
gcc/
2020-11-XX H.J. Lu
* configure.ac (HAVE_GAS_SHF_GNU_RETAIN): New. Define 1 if
the assembler supports marking sections with SHF_GNU_RETAIN flag.
* output.h (SECTION_RETAIN): New. Defined as 0x400.
(SECTION_MACH_DEP): Changed from 0x400 to 0x800.
(default_unique_section): Add a bool argument.
* varasm.c (get_section): Set SECTION_RETAIN for the preserved
symbol with HAVE_GAS_SHF_GNU_RETAIN.
(resolve_unique_section): Used named section for the preserved
symbol if assembler supports SHF_GNU_RETAIN.
(get_variable_section): Handle the preserved common symbol with
HAVE_GAS_SHF_GNU_RETAIN.
(default_elf_asm_named_section): Require the full declaration and
use the 'R' flag for SECTION_RETAIN.
* config.in: Regenerated.
* configure: Likewise.
gcc/testsuite/
2020-11-XX H.J. Lu
Jozef Lawrynowicz
* c-c++-common/attr-used.c: Check the 'R' flag.
* c-c++-common/attr-used-2.c: Likewise.
* c-c++-common/attr-used-3.c: New test.
* c-c++-common/attr-used-4.c: Likewise.
* gcc.c-torture/compile/attr-used-retain-1.c: Likewise.
* gcc.c-torture/compile/attr-used-retain-2.c: Likewise.
* lib/target-supports.exp
(check_effective_target_R_flag_in_section): New proc.
---
gcc/config.in | 7 +++
gcc/configure | 51 +++
gcc/configure.ac | 20
gcc/output.h | 6 ++-
gcc/testsuite/c-c++-common/attr-used-2.c | 1 +
gcc/testsuite/c-c++-common/attr-used-3.c | 7 +++
gcc/testsuite/c-c++-common/attr-used-4.c | 7 +++
gcc/testsuite/c-c++-common/attr-used.c| 1 +
.../compile/attr-used-retain-1.c | 32
.../compile/attr-used-retain-2.c | 15 ++
gcc/testsuite/lib/target-supports.exp | 40 +++
gcc/varasm.c | 17 +--
12 files changed, 200 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/c-c++-common/attr-used-3.c
create mode 100644 gcc/testsuite/c-c++-common/attr-used-4.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
diff --git a/gcc/config.in b/gcc/config.in
index b7c3107bfe3..23ae2f9bc1b 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -1352,6 +1352,13 @@
#endif
+/* Define 0/1 if your assembler supports marking sections with SHF_GNU_RETAIN
+ flag. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_SHF_GNU_RETAIN
+#endif
+
+
/* Define 0/1 if your assembler supports marking sections with SHF_MERGE flag.
*/
#ifndef USED_FOR_TARGET
diff --git a/gcc/configure b/gcc/configure
index dbda4415a17..a925a6e5efb 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -24272,6 +24272,57 @@ cat >>confdefs.h <<_ACEOF
_ACEOF
+# Test if the assembler supports the section flag 'R' for specifying
+# section with SHF_GNU_RETAIN.
+case "${target}" in
+ # Solaris may use GNU assembler with Solairs ld. Even if GNU
+ # assembler supports the section flag 'R', it doesn't mean that
+ # Solairs ld supports it.
+ *-*-solaris2*)
+gcc_cv_as_shf_gnu_retain=no
+;;
+ *)
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for section
'R' flag" >&5
+$as_echo_n "checking assembler for section 'R' flag... " >&6; }
+if ${gcc_cv_as_shf_gnu_retain+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ gcc_cv_as_shf_gnu_retain=no
+if test $in_tree_gas = yes; then
+if test $in_tree_gas_is_elf = yes \
+ && test $gcc_cv_gas_vers -ge `expr \( \( 2 \* 1000 \) + 36 \) \* 1000 + 0`
+ then gcc_cv_as_shf_gnu_retain=yes
+fi
+ elif test x$gcc_cv_as != x; then
+$as_echo '.section .foo,"awR",%progbits
+.byte 0' > conftest.s
+if { ac_try='$gcc_cv_as $gcc_cv_as_flags --fatal-warnings -o conftest.o
conftest.s >&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+then
+ gcc_cv_as_shf_gnu_retain=yes
+
