GHC's Linker Should Support Relocation Type 42

As per: https://github.com/DanielG/ghc-mod/issues/762#issuecomment-213743585

"gas >= 2.26 uses some new relocation types (in particular type 42, aka R_X86_64_REX_GOTPCRELX), which are not supported by ghc's linker."

This causes problems when linking in libs with certain sorts of c bits via the GHC API (at the very least).

Support should be added.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

Trac metadata

Trac field	Value
Component	Compiler → Runtime System (Linker)

assigned to @Phyx

Thanks for the report, this should be simple enough to fix

Trac metadata

Trac field	Value
Differential revisions	- → D2303

changed milestone to %8.0.2

changed weight to 7

I'm bumping the priority for this to 'high' (as GHC is technically broken on a new binutils in the static linker configuration) and moving it to 8.0.2.

Trac metadata

Trac field	Value
Priority	normal → high

I have "GNU assembler (GNU Binutils for Debian) 2.26" on my Debian system. but have not yet hit this issue. Is there a test case?

Tried this:

$ cabal get cipher-aes
$ cd cipher-aes-0.2.11
$ cabal sandbox init
$ cabal install --dependencies-only --enable-tests
$ cabal install
$ cabal exec -- ghci -i:Tests Tests/Tests.hs 
ghci > main
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
Ok, modules loaded: Crypto.Cipher.AES, Main, KATECB, KATCBC, KATXTS, KATGCM,
KATOCB3.
ghci > main
ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.3 for x86_64-unknown-linux):
    Loading temp shared object failed: /tmp/ghcc0a8_0/libghc_9.so: undefined
    symbol: aes_decrypt_ecb

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

That doesn't seem to be quite the same problem.

I haven't written a testcase since you need binutils-2.26 for it to trigger and I don't think I can force the test only then.

In any case, simplest case to reproduce this is to compile GHC with DYNAMIC_GHC_PROGRAMS=NO

I use this assembly file as input:

# x86_64
# as as_test.s -o as_test.o && objdump -Dr as_test.o
# ghc --interactive hs_test as_test.o

.text
.globl foo

foo:
	push %rbp
	mov %rsp, %rbp

	mov msg@GOTPCREL(%rip), %rdi
	call puts@PLT

	pop %rbp
	ret

.data
msg:
	.ascii "Hello World!\0"
	len = . - msg

Which with

[phyx@localhost ~]$ as --version
GNU assembler (GNU Binutils) 2.26.20160125

returns the expected relocation

[phyx@localhost ~]$ as as_test.s -o as_test.o && objdump -Dr as_test.o

as_test.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <foo>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   48 8b 3d 00 00 00 00    mov    0x0(%rip),%rdi        # b <foo+0xb>
                        7: R_X86_64_REX_GOTPCRELX       msg-0x4
   b:   e8 00 00 00 00          callq  10 <foo+0x10>
                        c: R_X86_64_PLT32       puts-0x4
  10:   5d                      pop    %rbp
  11:   c3                      retq

Disassembly of section .data:

0000000000000000 <msg>:
   0:   48                      rex.W
   1:   65 6c                   gs insb (%dx),%es:(%rdi)
   3:   6c                      insb   (%dx),%es:(%rdi)
   4:   6f                      outsl  %ds:(%rsi),(%dx)
   5:   20 57 6f                and    %dl,0x6f(%rdi)
   8:   72 6c                   jb     76 <len+0x69>
   a:   64 21 00                and    %eax,%fs:(%rax)

Before the patch it crashes as expected

[phyx@localhost ~]$ ghc/inplace/bin/ghc-stage2 --interactive as_test.o hs_test.hs
GHCi, version 8.1.20160604: http://www.haskell.org/ghc/  :? for help
ghc-stage2: as_test.o: unhandled ELF relocation(RelA) type 42

linking extra libraries/objects failed

And after the patch

GHCi, version 8.1.20160604: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( hs_test.hs, interpreted )
Ok, modules loaded: Main.
*Main> main
Hello World!

closed

NOTE: The bindist for elf platforms need to be build using a system that has glibc >= 2.23 in order for elf.h to contain these constants and for GHC to then be able to use them.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

mentioned in commit 0d963caf

reopened

Trac metadata

Trac field	Value
Resolution	ResolvedFixed → Unresolved

added 1 deleted label

@bgamari, is the a big enough issue to consider doing a 7.10.4 release?

Quoting @erikd in https://phabricator.haskell.org/D2303#67070:

I'm pretty sure that will be handled by the Linux distros. They wouldn't ship an GNU as until their glibc handled these new relocations.

We have our first victim of this assumption: https://github.com/snowleopard/hadrian/issues/259#issuecomment-224618414.