[ARM] Use different startfile and endfile for elf target when generating shared object.

Hi all,

GCC has startfile and endfile spec string built into it.
startfile is used to specify objects files to include at the start of 
the link process. While endfile, on the other hand, is used to specify 
objects files to include at the end of the link process.

crtbegin.o is one of the object files specified by startfile spec 
string. IIUC, crtbeginS.o should be used in place of crtbegin.o when 
generating shared objects.
The same applies to crtend.o which is one of the endfile. crtendS.o 
should be used when generating shared objects.

This patch makes the change to use different crtbegin and crtend files 
when creating shared and static object for elf toolchain. The linux 
toolchain already did this differentiation.

So when the toolchain doesn't support shared object, the following error 
message will be produced:
ld: cannot find crtbeginS.o: No such file or directory

Still, those specs strings built into GCC can be overridden by using
-specs=command-line switch to specify a spec file.

arm-none-eabi regression test without new issues, OK for trunk?

Regards,
Renlin Li

gcc/ChangeLog:

2016-06-16  Renlin Li  <renlin.li@arm.com>

	* config/arm/unknown-elf.h (UNKNOWN_ELF_STARTFILE_SPEC): Use
	crtbeginS.o for shared object.
	(UNKNOWN_ELF_ENDFILE_SPEC): Use crtendS.o for shared object.

Ping~

Regards,
Renlin

On 16/06/16 12:04, Renlin Li wrote:
> Hi all,
>
> GCC has startfile and endfile spec string built into it.
> startfile is used to specify objects files to include at the start of the link process.
> While endfile, on the other hand, is used to specify objects files to include at the end
> of the link process.
>
> crtbegin.o is one of the object files specified by startfile spec string. IIUC,
> crtbeginS.o should be used in place of crtbegin.o when generating shared objects.
> The same applies to crtend.o which is one of the endfile. crtendS.o should be used when
> generating shared objects.
>
> This patch makes the change to use different crtbegin and crtend files when creating
> shared and static object for elf toolchain. The linux toolchain already did this
> differentiation.
>
> So when the toolchain doesn't support shared object, the following error message will be
> produced:
> ld: cannot find crtbeginS.o: No such file or directory
>
> Still, those specs strings built into GCC can be overridden by using
> -specs=command-line switch to specify a spec file.
>
> arm-none-eabi regression test without new issues, OK for trunk?
>
> Regards,
> Renlin Li
>
> gcc/ChangeLog:
>
> 2016-06-16  Renlin Li  <renlin.li@arm.com>
>
>      * config/arm/unknown-elf.h (UNKNOWN_ELF_STARTFILE_SPEC): Use
>      crtbeginS.o for shared object.
>      (UNKNOWN_ELF_ENDFILE_SPEC): Use crtendS.o for shared object.

~ Ping

https://gcc.gnu.org/ml/gcc-patches/2016-06/msg01227.html

Regards,
Renlin

On 14/12/16 15:33, Renlin Li wrote:
> Ping~
>
> Regards,
> Renlin
>
> On 16/06/16 12:04, Renlin Li wrote:
>> Hi all,
>>
>> GCC has startfile and endfile spec string built into it.
>> startfile is used to specify objects files to include at the start of the link process.
>> While endfile, on the other hand, is used to specify objects files to include at the end
>> of the link process.
>>
>> crtbegin.o is one of the object files specified by startfile spec string. IIUC,
>> crtbeginS.o should be used in place of crtbegin.o when generating shared objects.
>> The same applies to crtend.o which is one of the endfile. crtendS.o should be used when
>> generating shared objects.
>>
>> This patch makes the change to use different crtbegin and crtend files when creating
>> shared and static object for elf toolchain. The linux toolchain already did this
>> differentiation.
>>
>> So when the toolchain doesn't support shared object, the following error message will be
>> produced:
>> ld: cannot find crtbeginS.o: No such file or directory
>>
>> Still, those specs strings built into GCC can be overridden by using
>> -specs=command-line switch to specify a spec file.
>>
>> arm-none-eabi regression test without new issues, OK for trunk?
>>
>> Regards,
>> Renlin Li
>>
>> gcc/ChangeLog:
>>
>> 2016-06-16  Renlin Li  <renlin.li@arm.com>
>>
>>      * config/arm/unknown-elf.h (UNKNOWN_ELF_STARTFILE_SPEC): Use
>>      crtbeginS.o for shared object.
>>      (UNKNOWN_ELF_ENDFILE_SPEC): Use crtendS.o for shared object.

Hi,

On 16/06/16 21:04, Renlin Li wrote:
>  /* Now we define the strings used to build the spec file.  */
> -#define UNKNOWN_ELF_STARTFILE_SPEC	" crti%O%s crtbegin%O%s crt0%O%s"
> +#define UNKNOWN_ELF_STARTFILE_SPEC	\
> +  "crti%O%s \
> +  %{!shared:crtbegin%O%s} %{shared:crtbeginS%O%s} \
> +  crt0%O%s"

Some targets seems to use shared|pie. When you change it, shouldn't it 
also include for pie?

Thanks,
Kugan

Hi Kugan,

some of the targets do include pie, and use the same crtbegin file as shared object.
For example, alpha/elf.h

And there are targets which don't do that,
For example, sh/elf.h

Most of the elf target seem only consider the simple case.

The purpose of this patch is to make it possible to correctly check whether current 
toolchain supports shared object.

Current dejegnu target selector "shared" tries to compile a simple source code to with 
"-shared -fpic" options to check whether "-shared" is supported.

For arm baremetal targets with, this is not sufficient.

arm-none-eabi is built with multilib. When running this testcase, if it's
compiled with "-march=armv7-a".
The crtbegin.o for this architecture version contains relocations which
cannot be used in shared object.
This test will fail.

if no cpu or architecture is specified, the default cpu will be arm7tdmi.
The test will pass as crtbegin.o for this version doesn't contains any relocations
only allowed in shared object.

To make this "shared" target selector work for arm baremetal toolchain. The correct way is 
to use different startup file for shared and non-shared toolchain.

If the toolchain doesn't support "-shared" option, and someone attempts to use it
to create shared object, it will complaint that "crtbeginS.o" cannot not be found.

A full history of discussion is here:
https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00322.html


Regards,
Renlin


On 12/01/17 11:47, kugan wrote:
> Hi,
>
> On 16/06/16 21:04, Renlin Li wrote:
>>  /* Now we define the strings used to build the spec file.  */
>> -#define UNKNOWN_ELF_STARTFILE_SPEC    " crti%O%s crtbegin%O%s crt0%O%s"
>> +#define UNKNOWN_ELF_STARTFILE_SPEC    \
>> +  "crti%O%s \
>> +  %{!shared:crtbegin%O%s} %{shared:crtbeginS%O%s} \
>> +  crt0%O%s"
>
> Some targets seems to use shared|pie. When you change it, shouldn't it also include for pie?
>
> Thanks,
> Kugan

Hi Renlin,


On 12 January 2017 at 16:50, Renlin Li <renlin.li@foss.arm.com> wrote:
> Hi Kugan,
>
> some of the targets do include pie, and use the same crtbegin file as shared
> object.
> For example, alpha/elf.h
>
> And there are targets which don't do that,
> For example, sh/elf.h
>
> Most of the elf target seem only consider the simple case.
>
> The purpose of this patch is to make it possible to correctly check whether
> current toolchain supports shared object.
>
> Current dejegnu target selector "shared" tries to compile a simple source
> code to with "-shared -fpic" options to check whether "-shared" is
> supported.
>
> For arm baremetal targets with, this is not sufficient.
>
> arm-none-eabi is built with multilib. When running this testcase, if it's
> compiled with "-march=armv7-a".
> The crtbegin.o for this architecture version contains relocations which
> cannot be used in shared object.
> This test will fail.
>
> if no cpu or architecture is specified, the default cpu will be arm7tdmi.
> The test will pass as crtbegin.o for this version doesn't contains any
> relocations
> only allowed in shared object.
>
> To make this "shared" target selector work for arm baremetal toolchain. The
> correct way is to use different startup file for shared and non-shared
> toolchain.
>
> If the toolchain doesn't support "-shared" option, and someone attempts to
> use it
> to create shared object, it will complaint that "crtbeginS.o" cannot not be
> found.
>

I have run validations with your patch, and noticed regressions on arm-none-eabi
when using default cpu or --with-cpu=cortex-m3:

  - PASS now FAIL             [PASS => FAIL]:

  gcc.dg/lto/pr54709 c_lto_pr54709_0.o-c_lto_pr54709_1.o link,  -fPIC
-fvisibility=hidden -flto
  gcc.dg/lto/pr61526 c_lto_pr61526_0.o-c_lto_pr61526_1.o link,  -fPIC
-flto -flto-partition=1to1
  gcc.dg/lto/pr64415 c_lto_pr64415_0.o-c_lto_pr64415_1.o link,  -O -flto -fpic

on the same configurations, I've noticed these improvements:

  g++.dg/ipa/devirt-28a.C  -std=gnu++11 (test for excess errors)
  g++.dg/ipa/devirt-28a.C  -std=gnu++14 (test for excess errors)
  g++.dg/ipa/devirt-28a.C  -std=gnu++98 (test for excess errors)
are now unsupported rather than fail.

Why is it different when the toolchain is configured --with-cpu=cortex-a9
for instance? Are the tests involving -shared already skipped in this case?

> A full history of discussion is here:
> https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00322.html
>
>
> Regards,
> Renlin
>
>
>
> On 12/01/17 11:47, kugan wrote:
>>
>> Hi,
>>
>> On 16/06/16 21:04, Renlin Li wrote:
>>>
>>>  /* Now we define the strings used to build the spec file.  */
>>> -#define UNKNOWN_ELF_STARTFILE_SPEC    " crti%O%s crtbegin%O%s crt0%O%s"
>>> +#define UNKNOWN_ELF_STARTFILE_SPEC    \
>>> +  "crti%O%s \
>>> +  %{!shared:crtbegin%O%s} %{shared:crtbeginS%O%s} \
>>> +  crt0%O%s"
>>
>>
>> Some targets seems to use shared|pie. When you change it, shouldn't it
>> also include for pie?
>>
>> Thanks,
>> Kugan

Hi Christophe,

Thanks for testing the patch!
I check the test case gcc.dg/lto/pr54709, it seems the test case is not properly written.

It add extra ld option -shared without checking the target support for that. After the 
change, this compilation will fail as a regression.
IIUC, '-shared' option is required, it should be gated with corresponding target selector.

"g++.dg/ipa/devirt-28a.C" now is skipped because of the target selector there.
// { dg-do link { target { { gld && fpic } && shared } } }

perhaps "gcc.dg/lto/pr54709" should do similar things like this:
// { dg-do link { target { shared } } }


As far as I know, with different cpu/arch configurations, different relocations are 
generated in the library, some of the relocations are not allowed to be used in shared
object.

With -march=armv7-a (and the --with-cpu=cortex-a9 option you mentioned), the linking stage 
of the test will fail because of this error:
"relocation XXX against external symbol `YYY' can not be used when making a shared object"
for instance: crtbegin.o: relocation R_ARM_MOVW_ABS_NC against `a local symbol` can not be 
used when making a shared object; recompile with -fPIC

If you are luck enough, for example with arm7tdmi cpu, no such relocation is generated in 
startup files. The "shared" target support check will pass for simple and naive code.
"--with-cpu=cortex-m3" should be this case. But the test cases which require shared object 
support will fail.


So this "shared" target checking mechanism is not reliable. The patch is to change this.



Regards,
Renlin



On 13/01/17 08:48, Christophe Lyon wrote:
> Hi Renlin,
>
>
> On 12 January 2017 at 16:50, Renlin Li <renlin.li@foss.arm.com> wrote:
>> Hi Kugan,
>>
>> some of the targets do include pie, and use the same crtbegin file as shared
>> object.
>> For example, alpha/elf.h
>>
>> And there are targets which don't do that,
>> For example, sh/elf.h
>>
>> Most of the elf target seem only consider the simple case.
>>
>> The purpose of this patch is to make it possible to correctly check whether
>> current toolchain supports shared object.
>>
>> Current dejegnu target selector "shared" tries to compile a simple source
>> code to with "-shared -fpic" options to check whether "-shared" is
>> supported.
>>
>> For arm baremetal targets with, this is not sufficient.
>>
>> arm-none-eabi is built with multilib. When running this testcase, if it's
>> compiled with "-march=armv7-a".
>> The crtbegin.o for this architecture version contains relocations which
>> cannot be used in shared object.
>> This test will fail.
>>
>> if no cpu or architecture is specified, the default cpu will be arm7tdmi.
>> The test will pass as crtbegin.o for this version doesn't contains any
>> relocations
>> only allowed in shared object.
>>
>> To make this "shared" target selector work for arm baremetal toolchain. The
>> correct way is to use different startup file for shared and non-shared
>> toolchain.
>>
>> If the toolchain doesn't support "-shared" option, and someone attempts to
>> use it
>> to create shared object, it will complaint that "crtbeginS.o" cannot not be
>> found.
>>
>
> I have run validations with your patch, and noticed regressions on arm-none-eabi
> when using default cpu or --with-cpu=cortex-m3:
>
>    - PASS now FAIL             [PASS => FAIL]:
>
>    gcc.dg/lto/pr54709 c_lto_pr54709_0.o-c_lto_pr54709_1.o link,  -fPIC
> -fvisibility=hidden -flto
>    gcc.dg/lto/pr61526 c_lto_pr61526_0.o-c_lto_pr61526_1.o link,  -fPIC
> -flto -flto-partition=1to1
>    gcc.dg/lto/pr64415 c_lto_pr64415_0.o-c_lto_pr64415_1.o link,  -O -flto -fpic
>
> on the same configurations, I've noticed these improvements:
>
>    g++.dg/ipa/devirt-28a.C  -std=gnu++11 (test for excess errors)
>    g++.dg/ipa/devirt-28a.C  -std=gnu++14 (test for excess errors)
>    g++.dg/ipa/devirt-28a.C  -std=gnu++98 (test for excess errors)
> are now unsupported rather than fail.
>
> Why is it different when the toolchain is configured --with-cpu=cortex-a9
> for instance? Are the tests involving -shared already skipped in this case?
>
>> A full history of discussion is here:
>> https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00322.html
>>
>>
>> Regards,
>> Renlin
>>
>>
>>
>> On 12/01/17 11:47, kugan wrote:
>>>
>>> Hi,
>>>
>>> On 16/06/16 21:04, Renlin Li wrote:
>>>>
>>>>   /* Now we define the strings used to build the spec file.  */
>>>> -#define UNKNOWN_ELF_STARTFILE_SPEC    " crti%O%s crtbegin%O%s crt0%O%s"
>>>> +#define UNKNOWN_ELF_STARTFILE_SPEC    \
>>>> +  "crti%O%s \
>>>> +  %{!shared:crtbegin%O%s} %{shared:crtbeginS%O%s} \
>>>> +  crt0%O%s"
>>>
>>>
>>> Some targets seems to use shared|pie. When you change it, shouldn't it
>>> also include for pie?
>>>
>>> Thanks,
>>> Kugan

On 13 January 2017 at 11:22, Renlin Li <renlin.li@foss.arm.com> wrote:
> Hi Christophe,
>
> Thanks for testing the patch!
> I check the test case gcc.dg/lto/pr54709, it seems the test case is not
> properly written.
>
> It add extra ld option -shared without checking the target support for that.
> After the change, this compilation will fail as a regression.
> IIUC, '-shared' option is required, it should be gated with corresponding
> target selector.
>
> "g++.dg/ipa/devirt-28a.C" now is skipped because of the target selector
> there.
> // { dg-do link { target { { gld && fpic } && shared } } }
>
> perhaps "gcc.dg/lto/pr54709" should do similar things like this:
> // { dg-do link { target { shared } } }
Quite likely, indeed.

>
>
> As far as I know, with different cpu/arch configurations, different
> relocations are generated in the library, some of the relocations are not
> allowed to be used in shared
> object.
>
> With -march=armv7-a (and the --with-cpu=cortex-a9 option you mentioned), the
> linking stage of the test will fail because of this error:
> "relocation XXX against external symbol `YYY' can not be used when making a
> shared object"
> for instance: crtbegin.o: relocation R_ARM_MOVW_ABS_NC against `a local
> symbol` can not be used when making a shared object; recompile with -fPIC
>
> If you are luck enough, for example with arm7tdmi cpu, no such relocation is
> generated in startup files. The "shared" target support check will pass for
> simple and naive code.
> "--with-cpu=cortex-m3" should be this case. But the test cases which require
> shared object support will fail.
>
>
> So this "shared" target checking mechanism is not reliable. The patch is to
> change this.
>
Shouldn't your patch imply that several tests move from "fail" to
"unsupported" on armv7-a ? I'm surprised not to see any difference in the
results.

>
>
> Regards,
> Renlin
>
>
>
>
> On 13/01/17 08:48, Christophe Lyon wrote:
>>
>> Hi Renlin,
>>
>>
>> On 12 January 2017 at 16:50, Renlin Li <renlin.li@foss.arm.com> wrote:
>>>
>>> Hi Kugan,
>>>
>>> some of the targets do include pie, and use the same crtbegin file as
>>> shared
>>> object.
>>> For example, alpha/elf.h
>>>
>>> And there are targets which don't do that,
>>> For example, sh/elf.h
>>>
>>> Most of the elf target seem only consider the simple case.
>>>
>>> The purpose of this patch is to make it possible to correctly check
>>> whether
>>> current toolchain supports shared object.
>>>
>>> Current dejegnu target selector "shared" tries to compile a simple source
>>> code to with "-shared -fpic" options to check whether "-shared" is
>>> supported.
>>>
>>> For arm baremetal targets with, this is not sufficient.
>>>
>>> arm-none-eabi is built with multilib. When running this testcase, if it's
>>> compiled with "-march=armv7-a".
>>> The crtbegin.o for this architecture version contains relocations which
>>> cannot be used in shared object.
>>> This test will fail.
>>>
>>> if no cpu or architecture is specified, the default cpu will be arm7tdmi.
>>> The test will pass as crtbegin.o for this version doesn't contains any
>>> relocations
>>> only allowed in shared object.
>>>
>>> To make this "shared" target selector work for arm baremetal toolchain.
>>> The
>>> correct way is to use different startup file for shared and non-shared
>>> toolchain.
>>>
>>> If the toolchain doesn't support "-shared" option, and someone attempts
>>> to
>>> use it
>>> to create shared object, it will complaint that "crtbeginS.o" cannot not
>>> be
>>> found.
>>>
>>
>> I have run validations with your patch, and noticed regressions on
>> arm-none-eabi
>> when using default cpu or --with-cpu=cortex-m3:
>>
>>    - PASS now FAIL             [PASS => FAIL]:
>>
>>    gcc.dg/lto/pr54709 c_lto_pr54709_0.o-c_lto_pr54709_1.o link,  -fPIC
>> -fvisibility=hidden -flto
>>    gcc.dg/lto/pr61526 c_lto_pr61526_0.o-c_lto_pr61526_1.o link,  -fPIC
>> -flto -flto-partition=1to1
>>    gcc.dg/lto/pr64415 c_lto_pr64415_0.o-c_lto_pr64415_1.o link,  -O -flto
>> -fpic
>>
>> on the same configurations, I've noticed these improvements:
>>
>>    g++.dg/ipa/devirt-28a.C  -std=gnu++11 (test for excess errors)
>>    g++.dg/ipa/devirt-28a.C  -std=gnu++14 (test for excess errors)
>>    g++.dg/ipa/devirt-28a.C  -std=gnu++98 (test for excess errors)
>> are now unsupported rather than fail.
>>
>> Why is it different when the toolchain is configured --with-cpu=cortex-a9
>> for instance? Are the tests involving -shared already skipped in this
>> case?
>>
>>> A full history of discussion is here:
>>> https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00322.html
>>>
>>>
>>> Regards,
>>> Renlin
>>>
>>>
>>>
>>> On 12/01/17 11:47, kugan wrote:
>>>>
>>>>
>>>> Hi,
>>>>
>>>> On 16/06/16 21:04, Renlin Li wrote:
>>>>>
>>>>>
>>>>>   /* Now we define the strings used to build the spec file.  */
>>>>> -#define UNKNOWN_ELF_STARTFILE_SPEC    " crti%O%s crtbegin%O%s
>>>>> crt0%O%s"
>>>>> +#define UNKNOWN_ELF_STARTFILE_SPEC    \
>>>>> +  "crti%O%s \
>>>>> +  %{!shared:crtbegin%O%s} %{shared:crtbeginS%O%s} \
>>>>> +  crt0%O%s"
>>>>
>>>>
>>>>
>>>> Some targets seems to use shared|pie. When you change it, shouldn't it
>>>> also include for pie?
>>>>
>>>> Thanks,
>>>> Kugan

Hi Christophe,

On 13/01/17 11:14, Christophe Lyon wrote:
> On 13 January 2017 at 11:22, Renlin Li <renlin.li@foss.arm.com> wrote:
>> Hi Christophe,
>>
>> Thanks for testing the patch!
>> I check the test case gcc.dg/lto/pr54709, it seems the test case is not
>> properly written.
>>
>> It add extra ld option -shared without checking the target support for that.
>> After the change, this compilation will fail as a regression.
>> IIUC, '-shared' option is required, it should be gated with corresponding
>> target selector.
>>
>> "g++.dg/ipa/devirt-28a.C" now is skipped because of the target selector
>> there.
>> // { dg-do link { target { { gld && fpic } && shared } } }
>>
>> perhaps "gcc.dg/lto/pr54709" should do similar things like this:
>> // { dg-do link { target { shared } } }
> Quite likely, indeed.
>
>>
>>
>> As far as I know, with different cpu/arch configurations, different
>> relocations are generated in the library, some of the relocations are not
>> allowed to be used in shared
>> object.
>>
>> With -march=armv7-a (and the --with-cpu=cortex-a9 option you mentioned), the
>> linking stage of the test will fail because of this error:
>> "relocation XXX against external symbol `YYY' can not be used when making a
>> shared object"
>> for instance: crtbegin.o: relocation R_ARM_MOVW_ABS_NC against `a local
>> symbol` can not be used when making a shared object; recompile with -fPIC
>>
>> If you are luck enough, for example with arm7tdmi cpu, no such relocation is
>> generated in startup files. The "shared" target support check will pass for
>> simple and naive code.
>> "--with-cpu=cortex-m3" should be this case. But the test cases which require
>> shared object support will fail.
>>
>>
>> So this "shared" target checking mechanism is not reliable. The patch is to
>> change this.
>>
> Shouldn't your patch imply that several tests move from "fail" to
> "unsupported" on armv7-a ? I'm surprised not to see any difference in the
> results.
>
>>

Oops, I reordered the explanation paragraphs in my last email, making it obscure.

The "shared" target check will fail on armv7-a architecture because of the reason
mentioned below. So they are already been ignored. After the change, they are still
marked as "unsupported", but with a different reason. "crtbeginS.o cannot be found"

The deja-gnu test framework will compose a small program to test whether the toolchain
supports "shared" option.

 >> With -march=armv7-a (and the --with-cpu=cortex-a9 option you mentioned), the
 >> linking stage of the test will fail because of this error:
 >> "relocation XXX against external symbol `YYY' can not be used when making a
 >> shared object"
 >> for instance: crtbegin.o: relocation R_ARM_MOVW_ABS_NC against `a local
 >> symbol` can not be used when making a shared object; recompile with -fPIC
 >>

So the check won't pass, and the test case is marked as "unsupported".

 >> If you are luck enough, for example with arm7tdmi cpu, no such relocation is
 >> generated in startup files. The "shared" target support check will pass for
 >> simple and naive code.
 >> "--with-cpu=cortex-m3" should be this case. But the test cases which require
 >> shared object support will fail.

So for the same test case,
With "--with-cpu=cortex-m3",
The "shared" target support check will pass. It is marked as supported, but fail to 
produce binary.
with --with-cpu=cortex-a9",
The "shared" target support check will fail. it is marked as "unsupported" and skipped.

After the change, the test case will marked as "unsupported" regardless of the
cpu/arch configuration.

Regards,
Renlin

On 13 January 2017 at 13:26, Renlin Li <renlin.li@foss.arm.com> wrote:
> Hi Christophe,
>
>
> On 13/01/17 11:14, Christophe Lyon wrote:
>>
>> On 13 January 2017 at 11:22, Renlin Li <renlin.li@foss.arm.com> wrote:
>>>
>>> Hi Christophe,
>>>
>>> Thanks for testing the patch!
>>> I check the test case gcc.dg/lto/pr54709, it seems the test case is not
>>> properly written.
>>>
>>> It add extra ld option -shared without checking the target support for
>>> that.
>>> After the change, this compilation will fail as a regression.
>>> IIUC, '-shared' option is required, it should be gated with corresponding
>>> target selector.
>>>
>>> "g++.dg/ipa/devirt-28a.C" now is skipped because of the target selector
>>> there.
>>> // { dg-do link { target { { gld && fpic } && shared } } }
>>>
>>> perhaps "gcc.dg/lto/pr54709" should do similar things like this:
>>> // { dg-do link { target { shared } } }
>>
>> Quite likely, indeed.
>>
>>>
>>>
>>> As far as I know, with different cpu/arch configurations, different
>>> relocations are generated in the library, some of the relocations are not
>>> allowed to be used in shared
>>> object.
>>>
>>> With -march=armv7-a (and the --with-cpu=cortex-a9 option you mentioned),
>>> the
>>> linking stage of the test will fail because of this error:
>>> "relocation XXX against external symbol `YYY' can not be used when making
>>> a
>>> shared object"
>>> for instance: crtbegin.o: relocation R_ARM_MOVW_ABS_NC against `a local
>>> symbol` can not be used when making a shared object; recompile with -fPIC
>>>
>>> If you are luck enough, for example with arm7tdmi cpu, no such relocation
>>> is
>>> generated in startup files. The "shared" target support check will pass
>>> for
>>> simple and naive code.
>>> "--with-cpu=cortex-m3" should be this case. But the test cases which
>>> require
>>> shared object support will fail.
>>>
>>>
>>> So this "shared" target checking mechanism is not reliable. The patch is
>>> to
>>> change this.
>>>
>> Shouldn't your patch imply that several tests move from "fail" to
>> "unsupported" on armv7-a ? I'm surprised not to see any difference in the
>> results.
>>
>>>
>
> Oops, I reordered the explanation paragraphs in my last email, making it
> obscure.
>
> The "shared" target check will fail on armv7-a architecture because of the
> reason
> mentioned below. So they are already been ignored. After the change, they
> are still
> marked as "unsupported", but with a different reason. "crtbeginS.o cannot be
> found"
>
> The deja-gnu test framework will compose a small program to test whether the
> toolchain
> supports "shared" option.
>
>>> With -march=armv7-a (and the --with-cpu=cortex-a9 option you mentioned),
>>> the
>>> linking stage of the test will fail because of this error:
>>> "relocation XXX against external symbol `YYY' can not be used when making
>>> a
>>> shared object"
>>> for instance: crtbegin.o: relocation R_ARM_MOVW_ABS_NC against `a local
>>> symbol` can not be used when making a shared object; recompile with -fPIC
>>>
>
> So the check won't pass, and the test case is marked as "unsupported".
>
>>> If you are luck enough, for example with arm7tdmi cpu, no such relocation
>>> is
>>> generated in startup files. The "shared" target support check will pass
>>> for
>>> simple and naive code.
>>> "--with-cpu=cortex-m3" should be this case. But the test cases which
>>> require
>>> shared object support will fail.
>
> So for the same test case,
> With "--with-cpu=cortex-m3",
> The "shared" target support check will pass. It is marked as supported, but
> fail to produce binary.
> with --with-cpu=cortex-a9",
> The "shared" target support check will fail. it is marked as "unsupported"
> and skipped.
>
> After the change, the test case will marked as "unsupported" regardless of
> the
> cpu/arch configuration.
>
OK thanks for the clarification.

> Regards,
> Renlin

Ping ~

On 14/12/16 15:33, Renlin Li wrote:
> Ping~
>
> Regards,
> Renlin
>
> On 16/06/16 12:04, Renlin Li wrote:
>> Hi all,
>>
>> GCC has startfile and endfile spec string built into it.
>> startfile is used to specify objects files to include at the start of the link process.
>> While endfile, on the other hand, is used to specify objects files to include at the end
>> of the link process.
>>
>> crtbegin.o is one of the object files specified by startfile spec string. IIUC,
>> crtbeginS.o should be used in place of crtbegin.o when generating shared objects.
>> The same applies to crtend.o which is one of the endfile. crtendS.o should be used when
>> generating shared objects.
>>
>> This patch makes the change to use different crtbegin and crtend files when creating
>> shared and static object for elf toolchain. The linux toolchain already did this
>> differentiation.
>>
>> So when the toolchain doesn't support shared object, the following error message will be
>> produced:
>> ld: cannot find crtbeginS.o: No such file or directory
>>
>> Still, those specs strings built into GCC can be overridden by using
>> -specs=command-line switch to specify a spec file.
>>
>> arm-none-eabi regression test without new issues, OK for trunk?
>>
>> Regards,
>> Renlin Li
>>
>> gcc/ChangeLog:
>>
>> 2016-06-16  Renlin Li  <renlin.li@arm.com>
>>
>>      * config/arm/unknown-elf.h (UNKNOWN_ELF_STARTFILE_SPEC): Use
>>      crtbeginS.o for shared object.
>>      (UNKNOWN_ELF_ENDFILE_SPEC): Use crtendS.o for shared object.