Compilation on Ubuntu 12.04 no longer succeeds

[alexcrichton]

A simple hello world fails with:

$ rustc foo.rs
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib" "foo.0.o" "-o" "foo" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,-Bdynamic" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/librand-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcollections-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_unicode-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc_jemalloc-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-1357b93f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-1357b93f.rlib" "-l" "dl" "-l" "pthread" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-l" "rt" "-l" "util"
  = note: /usr/bin/ld: /usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-1357b93f.rlib(fileline.o)(.debug_frame+0x6c): reloc against `.debug_frame': error 2
/usr/bin/ld: final link failed: Nonrepresentable section on output
collect2: ld returned 1 exit status


error: aborting due to previous error

Notably, this means that nightlies on Travis will fail to compile by default. Introduced at some point during cae6ab1...0ed9519, or maybe a recent change on the dist builder.

My money is currently on rust-lang-deprecated/rust-buildbot@a5d7cb7, but I have no idea why.

[alexcrichton]

Ok I'm now quite sure this was caused by rust-lang-deprecated/rust-buildbot@a5d7cb7.

The current container is working with binutils 2.27, the old container used 2.25.1, and I've also tested out 2.26. The results I got below were from a cargo build of the standard library in the container with the respective binutils version, all in the rust-slave-dist container base (just differing in binutils versions). Taking this compiled standard library I then attempted to link each standard library with a ubuntu 12.04 container with the following results

• Libstd built with 2.25 binutils worked, this is the state of the world before rust-lang-deprecated/rust-buildbot@a5d7cb7
• Libstd built with 2.26 binutils failed to compile with an assert in the linker
• Libstd built with 2.27 binutils failed to compile with the assert above

So overall this seems very similar to #34978 which happened because we updated from ubuntu 15.10 to 16.04, picking up a newer binutils version. That only affected the musl target, thankfully, though. The problem there was tracked down to a problem that was fixable, and we then since fixed it.

Searching through the gas changelog we can see two changes in 2.27 and 2.6 that seem relevant:

Changes in 2.27:

* Default to --enable-compressed-debug-sections=gas for Linux/x86 targets.

Changes in 2.26:

* --compress-debug-sections is turned on for Linux/x86 by default.

So with that in mind I passed --nocompress-debug-sections to the assembler via CFLAGS but I still got same error that the 2.26 build above got. Remembering #34978, though, I then also passed -mrelax-relocations=no and lo and behold it worked!

So tl;dr; we need to pass -mrelax-relocations basically everywhere, and we also need to pass --nocompress-debug-sections as well when compiling C code.

[alexcrichton]

(sorry for the double post, deleted the first one which I clicked post too soon on)

[alexcrichton]

IRC snippets:

15:10 <~acrichto> we have two options
15:10 <~acrichto> 1) revert back to binutils 2.25
15:10 <~acrichto> 2) pass two new fancy flags to disable the new behavior
15:10 <~acrichto> so (1) is quite easy, just go build a new container and call it a 
                  day
15:10 <~acrichto> will make rillian unhappy though
15:10 <~acrichto> unfortunately I don't think we can do (2) though
15:11 <~acrichto> passing two new fancy flags will break the rust build on a ton of 
                  platforms presumably which don't understand the flags
15:11 <~acrichto> and the last thing I want to do is to do feature detection here
15:11 <~acrichto> oh and I also don't know how to pass cflags just on the builders
15:11 <~acrichto> so my curret thinking for a plan of action is:
15:11 <~acrichto> a) revert back to binutils 2.25
15:11 <~acrichto> b) switch nightlies to use rustbuild
15:11 <~acrichto> c) update back to 2.27, but pass the fancy flags *only* on the 
                  builder
15:12 <~acrichto> where (c) is possible b/c rustflags is much easier to configure w/ 
                  CFLAGS env vars and whatnot
15:12 <~acrichto> or rather, I trust it a whole lot more

Building the revert back to 2.25 now

cc @rillian, this is going to revert the containers back to binutils 2.25, presumably breaking your i586 linux builds which you needed to fix your builds. We hope to upgrade back to 2.27 shortly, but just wanted to give you a heads up

[alexcrichton]

Ok, closing as the new image is now deployed. Hopefully tomorrow's nightly will have a fix for this, and if it doesn't we can reopen and rediagnose.