stdlib: tests: don't double-define _FORTIFY_SOURCE

  If using -D_FORITFY_SOURCE=3 (in my case, I've patched GCC to add
=3 instead of =2 (we've done =2 for years in Gentoo)), building
glibc tests will fail on testmb like:
```
<command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
<built-in>: note: this is the location of the previous definition
cc1: all warnings being treated as errors
make[2]: *** [../o-iterator.mk:9: /var/tmp/portage/sys-libs/glibc-2.36/work/build-x86-x86_64-pc-linux-gnu-nptl/stdlib/testmb.o] Error 1
make[2]: *** Waiting for unfinished jobs....
```

It's just because we're always setting -D_FORTIFY_SOURCE=2
rather than unsetting it first. If F_S is already 2, it's harmless,
but if it's another value (say, 1, or 3), the compiler will bawk.

(I'm not aware of a reason this couldn't be tested with =3,
but the toolchain support is limited for that (too new), and we want
to run the tests everywhere possible.)

Signed-off-by: Sam James <sam@gentoo.org>
---
 stdlib/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On 2022-08-05 16:13, Sam James via Libc-alpha wrote:
> If using -D_FORITFY_SOURCE=3 (in my case, I've patched GCC to add
> =3 instead of =2 (we've done =2 for years in Gentoo)), building
> glibc tests will fail on testmb like:
> ```
> <command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
> <built-in>: note: this is the location of the previous definition
> cc1: all warnings being treated as errors
> make[2]: *** [../o-iterator.mk:9: /var/tmp/portage/sys-libs/glibc-2.36/work/build-x86-x86_64-pc-linux-gnu-nptl/stdlib/testmb.o] Error 1
> make[2]: *** Waiting for unfinished jobs....
> ```
> 
> It's just because we're always setting -D_FORTIFY_SOURCE=2
> rather than unsetting it first. If F_S is already 2, it's harmless,
> but if it's another value (say, 1, or 3), the compiler will bawk.
> 
> (I'm not aware of a reason this couldn't be tested with =3,
> but the toolchain support is limited for that (too new), and we want
> to run the tests everywhere possible.)
> 
> Signed-off-by: Sam James <sam@gentoo.org>
> ---
>   stdlib/Makefile | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/stdlib/Makefile b/stdlib/Makefile
> index f7b25c1981..d8b59022cc 100644
> --- a/stdlib/Makefile
> +++ b/stdlib/Makefile
> @@ -380,7 +380,7 @@ CFLAGS-tst-qsort.c += $(stack-align-test-flags)
>   CFLAGS-tst-makecontext.c += -funwind-tables
>   CFLAGS-tst-makecontext2.c += $(stack-align-test-flags)
>   
> -CFLAGS-testmb.c += -D_FORTIFY_SOURCE=2 -Wall -Werror
> +CFLAGS-testmb.c += -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -Wall -Werror

I think we'll be better off with -D_FORTIFY_SOURCE=3 here since the 
intent is to test the fortified versions of the mb functions and =3 will 
give the maximum coverage.  The downside is that it will emit a warning 
when building with older gcc (because _FORTIFY_SOURCE=3 is not supported 
there and protection will downgrade to _FORTIFY_SOURCE=2) so the -Werror 
will need to go away and maybe even need -Wno-error.

Alternatively, some magic here to determine the maximum fortification 
level wouldn't hurt, but I won't gate your patch on that :)  I can work 
on that bit.

Thanks,
Sid
  

> On 8 Aug 2022, at 14:26, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> 
> On 2022-08-05 16:13, Sam James via Libc-alpha wrote:
>> If using -D_FORITFY_SOURCE=3 (in my case, I've patched GCC to add
>> =3 instead of =2 (we've done =2 for years in Gentoo)), building
>> glibc tests will fail on testmb like:
>> ```
>> <command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
>> <built-in>: note: this is the location of the previous definition
>> cc1: all warnings being treated as errors
>> make[2]: *** [../o-iterator.mk:9: /var/tmp/portage/sys-libs/glibc-2.36/work/build-x86-x86_64-pc-linux-gnu-nptl/stdlib/testmb.o] Error 1
>> make[2]: *** Waiting for unfinished jobs....
>> ```
>> It's just because we're always setting -D_FORTIFY_SOURCE=2
>> rather than unsetting it first. If F_S is already 2, it's harmless,
>> but if it's another value (say, 1, or 3), the compiler will bawk.
>> (I'm not aware of a reason this couldn't be tested with =3,
>> but the toolchain support is limited for that (too new), and we want
>> to run the tests everywhere possible.)
>> Signed-off-by: Sam James <sam@gentoo.org>
>> ---
>>  stdlib/Makefile | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/stdlib/Makefile b/stdlib/Makefile
>> index f7b25c1981..d8b59022cc 100644
>> --- a/stdlib/Makefile
>> +++ b/stdlib/Makefile
>> @@ -380,7 +380,7 @@ CFLAGS-tst-qsort.c += $(stack-align-test-flags)
>>  CFLAGS-tst-makecontext.c += -funwind-tables
>>  CFLAGS-tst-makecontext2.c += $(stack-align-test-flags)
>>  -CFLAGS-testmb.c += -D_FORTIFY_SOURCE=2 -Wall -Werror
>> +CFLAGS-testmb.c += -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -Wall -Werror
> 
> I think we'll be better off with -D_FORTIFY_SOURCE=3 here since the intent is to test the fortified versions of the mb functions and =3 will give the maximum coverage.  The downside is that it will emit a warning when building with older gcc (because _FORTIFY_SOURCE=3 is not supported there and protection will downgrade to _FORTIFY_SOURCE=2) so the -Werror will need to go away and maybe even need -Wno-error.
> 

This is a fair point, although I now see we've actually got libc_cv_predef_fortify_source
which sets CPPUNDEFS for exactly this sort of problem anyway.

I don't see the warning with gcc-11 + -Werror + F_S=3 on a test program. I can build some
older GCCs as I should probably keep them around anyway though.

> Alternatively, some magic here to determine the maximum fortification level wouldn't hurt, but I won't gate your patch on that :)  I can work on that bit.

I started looking at that and I'm not sure there's a point. includes/features.h downgrades us appropriately. I think we can unconditionally
set F_S=3 if I'm right about GCC not caring, as all the logic is on the glibc side, right?

We can always split this into two if you want:
1. The original commit (I can convert it to use libc_cv_predef_fortify_source's result) & backport it to 2.36
2. Another to crank to =3 and don't backport it in case I'm missing something.

> 
> Thanks,
> Sid

best,
sam
  

On 2022-08-08 18:30, Sam James wrote:
> This is a fair point, although I now see we've actually got libc_cv_predef_fortify_source
> which sets CPPUNDEFS for exactly this sort of problem anyway.
> 
> I don't see the warning with gcc-11 + -Werror + F_S=3 on a test program. I can build some
> older GCCs as I should probably keep them around anyway though.

Interesting, because you should have seen the warning about 
_FORTIFY_SOURCE=3 not being supported; I'm surprised that it doesn't 
fail due to that warning.

>> Alternatively, some magic here to determine the maximum fortification level wouldn't hurt, but I won't gate your patch on that :)  I can work on that bit.
> 
> I started looking at that and I'm not sure there's a point. includes/features.h downgrades us appropriately. I think we can unconditionally
> set F_S=3 if I'm right about GCC not caring, as all the logic is on the glibc side, right?

It's the warning I'm thinking about avoiding.

> 
> We can always split this into two if you want:
> 1. The original commit (I can convert it to use libc_cv_predef_fortify_source's result) & backport it to 2.36

Sounds good to me.

> 2. Another to crank to =3 and don't backport it in case I'm missing something.
> 

Thanks,
Sid
  

> On 10 Aug 2022, at 15:29, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> 
> On 2022-08-08 18:30, Sam James wrote:
>> This is a fair point, although I now see we've actually got libc_cv_predef_fortify_source
>> which sets CPPUNDEFS for exactly this sort of problem anyway.
>> I don't see the warning with gcc-11 + -Werror + F_S=3 on a test program. I can build some
>> older GCCs as I should probably keep them around anyway though.
> 
> Interesting, because you should have seen the warning about _FORTIFY_SOURCE=3 not being supported; I'm surprised that it doesn't fail due to that warning.

... and I see it now. I don't know what I did the other day. Oops.

> 
>>> Alternatively, some magic here to determine the maximum fortification level wouldn't hurt, but I won't gate your patch on that :)  I can work on that bit.
>> I started looking at that and I'm not sure there's a point. includes/features.h downgrades us appropriately. I think we can unconditionally
>> set F_S=3 if I'm right about GCC not caring, as all the logic is on the glibc side, right?
> 
> It's the warning I'm thinking about avoiding.
> 
>> We can always split this into two if you want:
>> 1. The original commit (I can convert it to use libc_cv_predef_fortify_source's result) & backport it to 2.36
> 
> Sounds good to me.
> 
>> 2. Another to crank to =3 and don't backport it in case I'm missing something.
> 

Okay, sounds like a plan, cheers. I'll get on it.

> Thanks,
> Sid
  

> On 10 Aug 2022, at 16:06, Sam James via Libc-alpha <libc-alpha@sourceware.org> wrote:
> 
> 
> 
>> On 10 Aug 2022, at 15:29, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>> 
>> On 2022-08-08 18:30, Sam James wrote:
>>> This is a fair point, although I now see we've actually got libc_cv_predef_fortify_source
>>> which sets CPPUNDEFS for exactly this sort of problem anyway.
>>> I don't see the warning with gcc-11 + -Werror + F_S=3 on a test program. I can build some
>>> older GCCs as I should probably keep them around anyway though.
>> 
>> Interesting, because you should have seen the warning about _FORTIFY_SOURCE=3 not being supported; I'm surprised that it doesn't fail due to that warning.
> 
> ... and I see it now. I don't know what I did the other day. Oops.
> 
>> 
>>>> Alternatively, some magic here to determine the maximum fortification level wouldn't hurt, but I won't gate your patch on that :)  I can work on that bit.
>>> I started looking at that and I'm not sure there's a point. includes/features.h downgrades us appropriately. I think we can unconditionally
>>> set F_S=3 if I'm right about GCC not caring, as all the logic is on the glibc side, right?
>> 
>> It's the warning I'm thinking about avoiding.
>> 
>>> We can always split this into two if you want:
>>> 1. The original commit (I can convert it to use libc_cv_predef_fortify_source's result) & backport it to 2.36
>> 
>> Sounds good to me.
>> 
>>> 2. Another to crank to =3 and don't backport it in case I'm missing something.
>> 
> 
> Okay, sounds like a plan, cheers. I'll get on it.
> 

I ended up getting frustrated with some over engineering and got distracted with fixing up
autoconf-archive's macro for it.

Could you push the this one or do you want me to resend it?

Cheers!
  

On 2023-02-02 13:21, Sam James wrote:
> I ended up getting frustrated with some over engineering and got distracted with fixing up
> autoconf-archive's macro for it.
> 
> Could you push the this one or do you want me to resend it?

Sorry I forgot to push it, done now.

Sid