Fails to build on x86_64-unknown-linux-gnux32 due to size mismatch (32 vs. 64 bits)

[glaubitz]

Trying to bootstrap rustc for x86_64-unknown-linux-gnux32 fails due to mismatching sizes for self.thread.as_pthread_t():

   Compiling jobserver v0.1.8
   Compiling env_logger v0.4.3
error[E0308]: mismatched types
   --> /home/glaubitz/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.8/src/lib.rs:628:40
    |
628 |                     libc::pthread_kill(self.thread.as_pthread_t(), libc::SIGUSR1);
    |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u64, found u32

error: aborting due to previous error

error: Could not compile `jobserver`.

Caused by:
  process didn't exit successfully: `/home/glaubitz/rust/rust/build/bootstrap/debug/rustc --crate-name jobserver /home/glaubitz/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.8/src/lib.rs --error-format json --crate-type lib --emit=dep-info,link -C opt-level=2 -C metadata=d0dd8f3422c113bb -C extra-filename=-d0dd8f3422c113bb --out-dir /home/glaubitz/rust/rust/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnux32/release/deps --target x86_64-unknown-linux-gnux32 -L dependency=/home/glaubitz/rust/rust/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnux32/release/deps -L dependency=/home/glaubitz/rust/rust/build/x86_64-unknown-linux-gnu/stage1-rustc/release/deps --extern libc=/home/glaubitz/rust/rust/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnux32/release/deps/liblibc-0d148f7402aae6cb.rlib --cap-lints allow` (exit code: 101)
warning: build failed, waiting for other jobs to finish...
error: build failed
thread 'main' panicked at 'command did not execute successfully: "/home/glaubitz/rust/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnux32" "--release" "--features" " jemalloc llvm" "--manifest-path" "/home/glaubitz/rust/rust/src/rustc/Cargo.toml" "--message-format" "json"
expected success, got: exit code: 101', src/bootstrap/compile.rs:873:8
note: Run with `RUST_BACKTRACE=1` for a backtrace.
failed to run: /home/glaubitz/rust/rust/build/bootstrap/debug/bootstrap build
Build completed unsuccessfully in 0:29:29
Makefile:22: recipe for target 'all' failed
make: *** [all] Error 1

[glaubitz]

I could fix this by casting the expression to u64:

glaubitz@z6:..rust/rust> diff -u /home/glaubitz/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.8/src/{lib.rs~,lib.rs}
--- /home/glaubitz/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.8/src/lib.rs~  2017-10-20 21:19:01.000000000 +0200
+++ /home/glaubitz/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.8/src/lib.rs   2017-10-22 18:38:32.223118424 +0200
@@ -625,7 +625,7 @@
                     // return an error, but on other platforms it may not. In
                     // that sense we don't actually know if this will succeed or
                     // not!
-                    libc::pthread_kill(self.thread.as_pthread_t(), libc::SIGUSR1);
+                    libc::pthread_kill(self.thread.as_pthread_t() as u64, libc::SIGUSR1);
                     match self.rx_done.recv_timeout(dur) {
                         Ok(()) |
                         Err(RecvTimeoutError::Disconnected) => {
glaubitz@z6:..rust/rust>

[alexcrichton]

Sounds like the libstd definition for pthread_t is wrong.

[glaubitz]

Yep, that's the problem.

For reference, see this small C test program:

glaubitz@z6:~> cat x32_test.c
#include <stdio.h>
#include <bits/pthreadtypes.h>

int main () {
  
  printf("The size of pthread_t is: %d\n", sizeof(pthread_t));
  printf("The size of unsigned long is: %d\n", sizeof(unsigned long));
  return 0;
}
glaubitz@z6:~> gcc -m64 x32_test.c -o x32_test_64
glaubitz@z6:~> gcc -mx32 x32_test.c -o x32_test_x32
glaubitz@z6:~> ./x32_test_64 
The size of pthread_t is: 8
The size of unsigned long is: 8
glaubitz@z6:~> ./x32_test_x32 
The size of pthread_t is: 4
The size of unsigned long is: 4
glaubitz@z6:~>

So, maybe Rust's assumption is wrong that c_ulong is 64 bits on x32?