Re: [PATCH] stdlib: tests: don't double-define _FORTIFY_SOURCE

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

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