howto cross-compile to get to work for powerpc e500v2

[th0ma7]

This relates to SynoCommunity spksrc project to build and package various open source software to run on Synology NAS.

I've been running into an issue where rust code cross-compiled for powerpc arch segfault (more specifically qoriq). The exact same code builds perfectly fine for all other archs (armv5, v7, aarch64, x86_64, i686). Ref: SynoCommunity/spksrc#5847 SynoCommunity/spksrc#5684

I've took two different approaches:

1. Using RUSTFLAGS to reproduce our CFLAGS used -mcpu=8548 -mhard-float -mfloat-gprs=double SynoCommunity/spksrc@90ad41d
2. Building a tier 3 powerpc-unknown-linux-gnuspe <<-- testing code only in my local branch for now

option 1

Using default powerpc-unknown-linux-gnu along with RUSTFLAGS = -Ctarget-cpu=e500 lead to the exact same result, seftault at startup. I may not be using the right RUSTFLAGS?

option 2

As for option 2 I feel I'm digging my own hole as I'm unable to build a powerpc-unknown-linux-gnuspe target using Synology provided toolchain and toolkit. I'm able to build up to stage1 & stage2 but unable to create a fully working target using cargo along with either my stage1 or stage2 builds... (clearly there is something I'm not fully understanding). Here's what I have so far:

git clone --depth 1 https://github.com/rust-lang/rust.git
./x setup compiler
PATH="$(WORK_DIR)/$(TC_TARGET)/bin:$${PATH}" ./x build --target $(RUST_TARGET)
rustup toolchain link powerpc-stage1 $(WORK_DIR)/rust/build/host/stage1
PATH="$(WORK_DIR)/$(TC_TARGET)/bin:$${PATH}" ./x build --stage 2 --target $(RUST_TARGET))
rustup toolchain link pwoerpc-stage2 $(WORK_DIR)/rust/build/host/stage2
--->> Up to this point all working OK <<---

Where it then fails:

rustup override set nightly
echo "[llvm]" >> $(WORK_DIR)/rust/config.toml
echo "allow-old-toolchain = true" >> $(WORK_DIR)/rust/config.toml   <<-- Presuming as `powerpc-e500v2-linux-gnuspe-gcc` is v4.9.3
PATH="$(WORK_DIR)/$(TC_TARGET)/bin:$${PATH}" POWERPC_UNKNOWN_LINUX_GNUSPE_OPENSSL_DIR=$(WORK_DIR)/../../../toolkit/syno-$(ARCH)-$(TCVERSION)/work/usr/ RUST_BACKTRACE=full cargo +$(firstword $(subst -, ,$(RUST_TARGET)))-stage1 build -Zbuild-std=core,alloc --target powerpc-unknown-linux-gnuspe

The error relates to llvm (enven though it did built it succesfully during either stage1 or stage2):

error: failed to run custom build command for `rustc_llvm v0.0.0 (/home/spksrc/qoriq-debug/spksrc/toolchain/syno-qoriq-6.2.4/work/rust/compiler/rustc_llvm)`
Caused by:
  process didn't exit successfully: `/home/spksrc/qoriq-debug/spksrc/toolchain/syno-qoriq-6.2.4/work/rust/target/debug/build/rustc_llvm-dc7ac9c0f6cecf54/build-script-build` (exit status: 101)
  --- stdout
  cargo:rustc-check-cfg=values(llvm_component,"ipo")
  cargo:rustc-check-cfg=values(llvm_component,"bitreader")
  cargo:rustc-check-cfg=values(llvm_component,"bitwriter")
  cargo:rustc-check-cfg=values(llvm_component,"linker")
  cargo:rustc-check-cfg=values(llvm_component,"asmparser")
  cargo:rustc-check-cfg=values(llvm_component,"lto")
  cargo:rustc-check-cfg=values(llvm_component,"coverage")
  cargo:rustc-check-cfg=values(llvm_component,"instrumentation")
  cargo:rustc-check-cfg=values(llvm_component,"x86")
  cargo:rustc-check-cfg=values(llvm_component,"arm")
  cargo:rustc-check-cfg=values(llvm_component,"aarch64")
  cargo:rustc-check-cfg=values(llvm_component,"amdgpu")
  cargo:rustc-check-cfg=values(llvm_component,"avr")
  cargo:rustc-check-cfg=values(llvm_component,"loongarch")
  cargo:rustc-check-cfg=values(llvm_component,"m68k")
  cargo:rustc-check-cfg=values(llvm_component,"csky")
  cargo:rustc-check-cfg=values(llvm_component,"mips")
  cargo:rustc-check-cfg=values(llvm_component,"powerpc")
  cargo:rustc-check-cfg=values(llvm_component,"systemz")
  cargo:rustc-check-cfg=values(llvm_component,"jsbackend")
  cargo:rustc-check-cfg=values(llvm_component,"webassembly")
  cargo:rustc-check-cfg=values(llvm_component,"msp430")
  cargo:rustc-check-cfg=values(llvm_component,"sparc")
  cargo:rustc-check-cfg=values(llvm_component,"nvptx")
  cargo:rustc-check-cfg=values(llvm_component,"hexagon")
  cargo:rustc-check-cfg=values(llvm_component,"riscv")
  cargo:rustc-check-cfg=values(llvm_component,"bpf")
  cargo:rerun-if-env-changed=RUST_CHECK
  cargo:rerun-if-env-changed=REAL_LIBRARY_PATH_VAR

  --- stderr
  thread 'main' panicked at compiler/rustc_llvm/build.rs:51:59:
  REAL_LIBRARY_PATH_VAR
  stack backtrace:
     0: rust_begin_unwind
     1: core::panicking::panic_fmt
     2: core::option::expect_failed
     3: core::option::Option<T>::expect
               at /home/spksrc/qoriq-debug/spksrc/toolchain/syno-qoriq-6.2.4/work/rust/library/core/src/option.rs:888:21
     4: build_script_build::restore_library_path
               at ./build.rs:51:15
     5: build_script_build::main
               at ./build.rs:113:5
     6: core::ops::function::FnOnce::call_once
               at /home/spksrc/qoriq-debug/spksrc/toolchain/syno-qoriq-6.2.4/work/rust/library/core/src/ops/function.rs:250:5
  note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
warning: build failed, waiting for other jobs to finish...
make[2]: *** [../../mk/spksrc.tc-rust.mk:64: rustc_target] Error 101
/home/spksrc/qoriq-debug/spksrc/cross/bat/work-qoriq-6.2.4/tc_vars.mk:1: *** An error occured while setting up the toolchain, please check the messages above.  Stop.
make[1]: Leaving directory '/home/spksrc/qoriq-debug/spksrc/cross/bat'

option 3

Now, further reading and as option 3 I may be able to "rebuild" tier 1 powerpc-unknown-linux-gnu by adding the proper target features such as #117347 . But guessing I'd have to run through the same procession as option 2 ?

[saethlin]

Using default powerpc-unknown-linux-gnu along with RUSTFLAGS = -Ctarget-cpu=e500 lead to the exact same result, seftault at startup. I may not be using the right RUSTFLAGS?

You are using a tier 2 target. Can you compile any programs successfully? It's not clear to me from your description that this is not a miscompile.

[th0ma7]

You are using a tier 2 target. Can you compile any programs successfully? It's not clear to me from your description that this is not a miscompile.

@saethlin nope, no programs seems to runs on the qoriq platform using powerpc-unknown-linux-gnu with or without RUSTFLAGS = -Ctarget-cpu=e500. Which is why I'm wondering if I'm using the right target? Or missing build flags... ?

[workingjubilee]

Try -Ctarget-cpu=e500mc

[workingjubilee]

I'm confused, you said QoriQ, but then you said you're targeting MPC8548? Which is it? No, they're not necessarily guaranteed to be compatible: ignore the vendor's claims otherwise and approach this empirically.

[workingjubilee]

You use a vendor-provided (and thus possibly patched?) gcc, so it seems plausible to me that LLVM might have a different model of the CPU capabilities. Can you use clang to build, instead of gcc, for this target, and get working binaries? Or even a stock gcc?

You also made a typo:
rustup toolchain link pwoerpc-stage2 $(WORK_DIR)/rust/build/host/stage2