Re: [PATCH 0/3] Allow LLD 13.0.0 and improve compatibility with gold and clang

["H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>]

On Sun, Jul 25, 2021 at 8:58 PM Fangrui Song via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> The patches allow LLD 13.0.0 to build glibc. LLD's compatibility with
> GNU ld is generally better than gold's compatibility with GNU ld.
>
> The first two commits improve gold and clang compatibility as well.
> (There is still a long way for clang to build glibc.)
>
> About `make check` results:
>
> I can't configure glibc --enable-static-pie with gold, so I use
> --disable-static-pie with gold.
>
> * gold (--disable-static-pie) has 160 FAIL.
> * ld.bfd has 152 FAIL.
> * ld.lld has 159 FAIL.
>
> ## I have investigated a few failures.
>
> The tst-ifunc-isa-*.c failures are not ld.lld's fault.
> The lld linked tst-ifunc-isa-* work with LD_BIND_NOW=1.
> The tests happen to work with GNU ld because the IRELATIVE for foo_ifunc
> is placed after JUMP_SLOT in .repa.plt.  The test needs to call
> __x86_get_cpuid_feature_leaf which is defined in a different TU. IMHO
> such ifunc does not guaranteed to work.
>
> For gmon/tst-gmon-gprof*, ld.lld linked tst-gmon-gprof has a f3 line,
> which appears more correct to me.  But the test considers it a failure.
>
> % cat gmon/tst-gmon-gprof.out
> --- expected
> +++ actual
> @@ -1,2 +1,3 @@
>  f1 2000
>  f2 1000
> +f3 1
> FAIL
>
>
> For malloc/tst-compathooks-on,
>
>     malloc/tst-compathooks-on: Symbol `__free_hook' has different size in shared object, consider re-linking
>
> the root cause is that lld's symbol versioning is different from GNU ld in an unusal case:
>
>     __asm__ (".symver " "__free_hook" "," "__free_hook" "@" "GLIBC_2.2.5");
>
> This leaves two symbols __free_hook and __free_hook@GLIBC_2.2.5.
> __free_hook is then attached a default version GLIBC_2.2.5.
> I think malloc/malloc-debug.c uses a fragile versioned symbol here.
> If the inline asm uses @@ the failure should go away.
>
>
> In summary, I think the failed tests touch some dark corners of the toolchain.
> These things do not really matter for real world applications.
>

Please open a separate bug for each issue you are trying to fix and reference
the bug in your patch.

Thanks.

-- 
H.J.