Re: lld status with powerpc64

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 05/11/2021 10:58, Adhemerval Zanella wrote:

> So we have two options here:
> 
>   1. Do not define USE_PPC64_NOTOC if with-lld (not optimal if ldd
>      aims to support such behavior).
> 
>   2. Define USE_PPC64_NOTOC iff linker supports such optimization.
>      It means to emit a NOTOC relocation (R_PPC64_REL24_NOTOC),
>      link a simple binary without any pcrel and check if the stub has 
>      power10 instruction.
> 
>   3. Remove the USE_PPC64_NOTOC usage.  It is used on setjmp routines
>      and on the syscall definition to call the __syscall_error.
> 
> I am aiming to implement 2. since at least by disabling USE_PPC64_NOTOC 
> manually on config.h when configuring with lld I can build glibc.
> 
>>
>>
>> In my testing environment (POWER9), ld.bfd doesn't support @notoc, so
>> USE_PPC64_NOTOC is undefined.
>>
>> % gcc --version
>> gcc (Debian 8.3.0-6) 8.3.0
>> ...
>> % ld.bfd --version
>> GNU ld (GNU Binutils for Debian) 2.31.1
>> ...
>>
>> I only see 8 more FAILs with ld.lld than ld.bfd
> 
> I am still having trouble to *finish* make check with lld release 13
> my environment (some tests stuck on infinite loop).
> 
>>
>>
>> % diff -u 0 1
>> --- 0   2021-11-05 00:11:43.218731302 -0700
>> +++ 1   2021-11-05 00:11:37.659286448 -0700
>> @@ -9,6 +9,14 @@
>>  FAIL: debug/tst-lfschk6
>>  FAIL: dlfcn/bug-atexit3
>>  FAIL: elf/check-abi-libc
>> +FAIL: elf/ifuncmain1pic
>> +FAIL: elf/ifuncmain1pie
>> +FAIL: elf/ifuncmain1vis
>> +FAIL: elf/ifuncmain1vispic
>> +FAIL: elf/ifuncmain1vispie
>> +FAIL: elf/ifuncmain3
>> +FAIL: elf/ifuncmain6pie
>> +FAIL: elf/tst-tlsopt-powerpc
>>  FAIL: nptl/tst-cancel24
>>  FAIL: nptl/tst-minstack-throw
>>  FAIL: nptl/tst-once5
>>
>>
>> I suspect ifuncmain1* is again related to the order of R_*_IRELATIVE with
>> regard to R_*_JUMP_SLOT referencing a STT_GNU_IFUNC symbol.
>> (something like https://maskray.me/blog/2021-01-18-gnu-indirect-function#relocation-resolving-order)
>> But perhaps Adhemerval can look a look at it.
> 
> I still need to understand why armhf also fails with the ifunc using
> protected symbols, although I am not if they are related to IRELATIVE
> ordering.
> 
>>
>>
>> For elf/tst-tlsopt-powerpc, it is simply because ld.lld doesn't implement the GNU ld powerpc64's
>> __tls_get_addr_opt (pseudo-TLSDESC): https://maskray.me/blog/2021-02-14-all-about-thread-local-storage#powerpc-__tls_get_addr_opt
>> Let me send a configure patch to disable it...
>>
>> Actually I do not know how to disable tst-tlsopt-powerpc properly.
>>
>> Perhaps add sysdeps/powerpc/configure.ac and move the
>> sysdeps/unix/sysv/linux/powerpc/configure.ac --no-tls-get-addr-optimize
>> to sysdeps/powerpc/configure.ac?
>> sysdeps/powerpc/preconfigure.ac exists (I don't know how it is used).
>>
>> The patch requires some non-trivial configure.ac change, so I'd hope
>> that an expert can do it 
> 
> Maybe just disable the test if __tls_get_addr_opt (pseudo-TLSDESC) is not supported
> by the linker?
> 
> 
>>
>>
>> Hey, so lld linked glibc powerpc64 is in a pretty good status!
> 
> I am still not sure about it, I did could run some tests but I am still
> struggling to get a make check to finish.
> 

So it turned out the another issues was my gcc toolchain did not have
initfini array set which lets to compiler generate .ctors instead of
.init_array and lld does not support .ctors (it just ignores instead of
converting to .init_array entries as bfd).

With NOTOC fix and a proper toolchain I am seeing the same regression
you are seeing:

FAIL: elf/ifuncmain1pic
FAIL: elf/ifuncmain1pie
FAIL: elf/ifuncmain1vis
FAIL: elf/ifuncmain1vispic
FAIL: elf/ifuncmain1vispie
FAIL: elf/ifuncmain3
FAIL: elf/ifuncmain6pie
FAIL: elf/tst-tlsopt-powerpc

I think it would be good use --enable-initfini-array on build-many-glibc.py
until we set gcc-12 as default.