[PATCH 0/3] Improve lld support and current status

[Adhemerval Zanella]

Ths patch allows x86_64, i686, aarch64, powerpc64le, powerpc64, and
powerpc to build, including the tests, with LLD packed in LLVM 13 [1].

For x86_64 and aarch64 there is no regression in testssuite.  On 
i686 there is only one:

  FAIL: elf/ifuncmain6pie

Which segfaults calling the 'foo' functions:

  Program received signal SIGSEGV, Segmentation fault.
  0xfb010101 in ?? ()
  (gdb) bt
  #0  0xfb010101 in ?? ()
  #1  0xf7fba620 in call_foo () at ifuncmod6.c:18
  #2  0xf7fc0857 in ?? ()
  #3  0xf7e1b195 in __libc_start_call_main (main=main@entry=0xf7fc0830,
  argc=argc@entry=2, argv=argv@entry=0xffffc610) at
  ../sysdeps/nptl/libc_start_call_main.h:58
  #4  0xf7e1b286 in __libc_start_main_impl (main=0xf7fc0830, argc=2,
  argv=0xffffc610, init=0x0, fini=0x0, rtld_fini=0xf7fe79b0 <_dl_fini>,
  stack_end=0xffffc60c) at ../csu/libc-start.c:409
  #5  0xf7fc06d7 in ?? ()

The powerpc64le fails at libc.so start:

  (gdb) bt
  #0  0x00007ffff7f2a980 in __gep_setup___vmx__sigjmp_save ()
    from
  /home/azanella/glibc/build/powerpc64le-linux-gnu-power9-lld/libc.so.6
  #1  0x00007ffff7d7ac5c in __libc_start_call_main ()
     from
  /home/azanella/glibc/build/powerpc64le-linux-gnu-power9-lld/libc.so.6
  #2  0x00007ffff7d7ae90 in __libc_start_main_impl ()
     from
  /home/azanella/glibc/build/powerpc64le-linux-gnu-power9-lld/libc.so.6
  #3  0x0000000000000000 in ?? ()
  (gdb) disas
  Dump of assembler code for function __gep_setup___vmx__sigjmp_save:
  => 0x00007ffff7f2a980 <+0>:     .long 0x613ffe6
     0x00007ffff7f2a984 <+4>:     li      r12,-1280
     0x00007ffff7f2a988 <+8>:     mtctr   r12
     0x00007ffff7f2a98c <+12>:    bctr

And powerpc64-linux-gnu fails on dynamic loaders start:

  (gdb) bt
  #0  0x00007ffff7ffa9a8 in _start ()
  (gdb) disas
  Dump of assembler code for function _start:
  => 0x00007ffff7ffa9a8 <+0>:     .long 0x0
     0x00007ffff7ffa9ac <+4>:     .long 0x0
     0x00007ffff7ffa9b0 <+8>:     .long 0x0
     0x00007ffff7ffa9b4 <+12>:    .long 0x0


The arm, sparcv9, mips, and riscv fail to build due different issues. On
arm the loader fails to build:

  ld.so fails with
  ld.lld: error: relocation R_ARM_GOTOFF32 cannot be used against symbol
  _dl_argv; recompile with -fPIC
  >>> defined in
  >>> /home/azanella/Projects/glibc/build/arm-linux-gnueabihf-lld/elf/librtld.os
  >>> referenced by rtld.c:164
  >>>               /home/azanella/Projects/glibc/build/arm-linux-gnueabihf-lld/elf/librtld.os:(.text+0xA8)

On sparcv9, lld handles --relax option different than ld.bfd: it throws
an error instead of silent ignoring it:

  $ sparc64-glibc-linux-gnu-gcc -mcpu=niagara -fuse-ld=lld -Bclang+llvm-13.0.0-x86_64-linux-gnu-ubuntu-20.04/bin
    -g -O2 -fPIC -shared -fno-stack-protector -o conftest.so conftest.c -nostdlib -nostartfiles -Wl,-z,combreloc
  ld.lld: error: unknown argument '-relax'

And even when -mno-relax is explicit add, lld does not support some relocations
generated by GCC:

  $ sparc64-glibc-linux-gnu-readelf -Wr elf/librtld.os | grep _dl_skip_args
  | head -n2
  00000000000000a0  0000012200000052 R_SPARC_GOTDATA_OP_HIX22
  0000000000000058 _dl_skip_args + 0
  00000000000000a4  0000012200000053 R_SPARC_GOTDATA_OP_LOX10
  0000000000000058 _dl_skip_args + 0

The mips/mipsel also fails to build the loader:

  ld.lld: error: can't create dynamic relocation R_MIPS_32 against local
  symbol in readonly segment; recompile object files with -fPIC or pass
  '-Wl,-z,notext' to allow text relocations in the output
  >>> defined in
  >>> /home/azanella/Projects/glibc/build/mips-linux-gnu-lld/elf/librtld.os
  >>> referenced by /home/azanella/toolchain/src/gcc/libgcc/libgcc2.c
  >>>               /home/azanella/Projects/glibc/build/mips-linux-gnu-lld/elf/librtld.os:(.eh_frame+0x1C)

  ld.lld: error: can't create dynamic relocation R_MIPS_32 against local
  symbol in readonly segment; recompile object files with -fPIC or pass
  '-Wl,-z,notext' to allow text relocations in the output
  >>> defined in
  >>> /home/azanella/Projects/glibc/build/mips-linux-gnu-lld/elf/librtld.os
  >>> referenced by /home/azanella/toolchain/src/gcc/libgcc/libgcc2.c
  >>>               /home/azanella/Projects/glibc/build/mips-linux-gnu-lld/elf/librtld.os:(.eh_frame+0x54)

Similar to mips64/mips64el:

  ld.lld: warning: ../sysdeps/unix/sysv/linux/setitimer.c:(function
  _dl_runtime_resolve: .text+0x18954): found R_MIPS_JALR relocation
  against non-function symbol . This is invalid and most likely a compiler
  bug.
  ld.lld: error: can't create dynamic relocation R_MIPS_64 against local
  symbol in readonly segment; recompile object files with -fPIC or pass
  '-Wl,-z,notext' to allow text relocations in the output
  >>> defined in
  >>> /home/azanella/Projects/glibc/build/mips64-linux-gnu-lld/elf/librtld.os
  >>> referenced by ../sysdeps/unix/sysv/linux/setitimer.c
  >>>               /home/azanella/Projects/glibc/build/mips64-linux-gnu-lld/elf/librtld.os:(.eh_frame+0x20)

The riscv32/riscv64 fails to the loader, but it is due missing support
to relaxation:

  ld.lld: error:
  /home/azanella/Projects/glibc/glibc-git/elf/rtld.c:2584:(.text+0xEC84):
  relocation R_RISCV_ALIGN requires unimplemented linker relaxation;
  recompile with -mno-relax
  ld.lld: error:
  /home/azanella/Projects/glibc/glibc-git/elf/rtld.c:2589:(.text+0x13DEC):
  relocation R_RISCV_ALIGN requires unimplemented linker relaxation;
  recompile with -mno-relax
  ld.lld: error:
  /home/azanella/Projects/glibc/glibc-git/elf/rtld.c:2589:(.text+0x13DEE):
  relocation R_RISCV_ALIGN requires unimplemented linker relaxation;
  recompile with -mno-rela

Adding -mno-relax to sysdep-CFLAGS seems to be ineffective.


[1] https://releases.llvm.org/download.html#13.0.0

Adhemerval Zanella (3):
  elf: Disable ifuncmain{1,5,5pic,5pie} when using LLD
  Fix LIBC_PROG_BINUTILS for -fuse-ld=lld
  Check if linker also support -mtls-dialect=gnu2

 aclocal.m4   |  6 +++++-
 configure    | 10 +++++++---
 configure.ac |  4 ++--
 elf/Makefile | 17 +++++++++++++----
 4 files changed, 27 insertions(+), 10 deletions(-)

-- 
2.32.0