librustc_codegen_llvm: Pass bitflags as raw integral types for FFI (#61306)

[jrtc27]

The C++ side uses enums with underlying integral types. However, Rust's bitflags types are a single-field struct containing an integral type, which are not always passed the same way in the C ABI. In particular, sparc64's ABI extends integral types to a full 64-bit value, but does not do the same for single-field structs. Thanks to Michael Karcher for finding this bug.

[rust-highfive]

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[jrtc27]

@psumbera / @glaubitz - could you please test whether this fixes the bug?

[glaubitz]

I think you need to adjust the imports used:

error: unused import: `DISPFlags`=================================>    ] 14/15: rustc_codegen_llvm                                                                        
 --> src/librustc_codegen_llvm/llvm/ffi.rs:5:27
  |
5 |     DINameSpace, DIFlags, DISPFlags, DebugEmissionKind,
  |                           ^^^^^^^^^
  |
  = note: `-D unused-imports` implied by `-D warnings`

error: aborting due to previous error

error: Could not compile `rustc_codegen_llvm`.

Since you no longer use DISPFlags.

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:000511ae:start=1560603739665838614,finish=1560603740457916787,duration=792078173
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
[00:26:09]    Compiling rustc-demangle v0.1.15
[00:26:13]    Compiling memmap v0.6.2
[00:26:14]    Compiling num_cpus v1.8.0
[00:26:17]    Compiling rustc_llvm v0.0.0 (/checkout/src/librustc_llvm)
[00:26:22] error: unused import: `DISPFlags`
[00:26:22]  --> src/librustc_codegen_llvm/llvm/ffi.rs:5:27
[00:26:22]   |
[00:26:22] 5 |     DINameSpace, DIFlags, DISPFlags, DebugEmissionKind,
[00:26:22]   |
[00:26:22]   = note: `-D unused-imports` implied by `-D warnings`
[00:26:22] 
[00:26:24] error: aborting due to previous error
---
travis_time:end:081a19c4:start=1560605336991578483,finish=1560605336996960140,duration=5381657
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:017311b1
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:20566ec

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[jrtc27]

@glaubitz Travis has now passed that error, could you please retry?

[glaubitz]

Already working on it :).

[glaubitz]

I can confirm that this patch fixes the problem for me. Will do a full rebuild now just to be sure there are no side effects.

[glaubitz]

Oh, I just realized you changed the patch quite a lot. I used the first version of the patch and just removed the unused import.

[glaubitz]

I have just finished testing the latest version of the patch and I can confirm it fixes the problem for me.

I just cross-built rustc from git for sparc64, copied it over to a sparc64 machine and did a full successful native build of rustc from git on sparc64 with this patch applied to the sources.

[petrochenkov]

I suspect that you may be able to put #[repr(transparent)] on the bitflag structures instead and it will fix the ABI automatically.
Could you check whether that works?

[glaubitz]

Okay, testing this change now:

diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index a71243c7c8..5ef0e6246b 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -566,6 +566,7 @@ pub mod debuginfo {
     bitflags! {
         #[repr(C)]
         #[derive(Default)]
+        #[repr(transparent)]
         pub struct DIFlags: ::libc::uint32_t {
             const FlagZero                = 0;
             const FlagPrivate             = 1;
@@ -595,6 +596,7 @@ pub mod debuginfo {
     bitflags! {
         #[repr(C)]
         #[derive(Default)]
+        #[repr(transparent)]
         pub struct DISPFlags: ::libc::uint32_t {
             const SPFlagZero              = 0;
             const SPFlagVirtual           = 1;

[glaubitz]

This seems to work:

diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index a71243c7c8..a5c295cd45 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -564,7 +564,7 @@ pub mod debuginfo {
 
     // These values **must** match with LLVMRustDIFlags!!
     bitflags! {
-        #[repr(C)]
+        #[repr(transparent)]
         #[derive(Default)]
         pub struct DIFlags: ::libc::uint32_t {
             const FlagZero                = 0;
@@ -593,7 +593,7 @@ pub mod debuginfo {
 
     // These values **must** match with LLVMRustDISPFlags!!
     bitflags! {
-        #[repr(C)]
+        #[repr(transparent)]
         #[derive(Default)]
         pub struct DISPFlags: ::libc::uint32_t {
             const SPFlagZero              = 0;

[glaubitz]

I have created #61881 now.

[petrochenkov]

Closing in favor of #61881