From 4450807ead1c5f9a5f8d44ffee6ed0f968c68c34 Mon Sep 17 00:00:00 2001 From: Jan Niehusmann Date: Tue, 30 May 2017 17:50:44 +0200 Subject: [PATCH] ARMv5 needs +strict-align Without that flag, LLVM generates unaligned memory access instructions, which are not allowed on ARMv5. For example, the 'hello world' example from `cargo --new` failed with: ``` $ ./hello Hello, world! thread 'main' panicked at 'assertion failed: end <= len', src/libcollections/vec.rs:1113 note: Run with `RUST_BACKTRACE=1` for a backtrace. ``` I traced this error back to the following assembler code in `BufWriter::flush_buf`: ``` 6f44: e28d0018 add r0, sp, #24 [...] 6f54: e280b005 add fp, r0, #5 [...] 7018: e5cd001c strb r0, [sp, #28] 701c: e1a0082a lsr r0, sl, #16 7020: 03a01001 moveq r1, #1 7024: e5cb0002 strb r0, [fp, #2] 7028: e1cba0b0 strh sl, [fp] ``` Note that `fp` points to `sp + 29`, so the three `str*`-instructions should fill up a 32bit - value at `sp + 28`, which is later used as the value `n` in `Ok(n) => written += n`. This doesn't work on ARMv5 as the `strh` can't write to the unaligned contents of `fp`, so the upper bits of `n` won't get cleared, leading to the assertion failure in Vec::drain. With `+strict-align`, the code works as expected. --- src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs b/src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs index 200c6ab74cc6d..ef00c9a3278b9 100644 --- a/src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs +++ b/src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs @@ -25,7 +25,7 @@ pub fn target() -> TargetResult { linker_flavor: LinkerFlavor::Gcc, options: TargetOptions { - features: "+soft-float".to_string(), + features: "+soft-float,+strict-align".to_string(), // No atomic instructions on ARMv5 max_atomic_width: Some(0), abi_blacklist: super::arm_base::abi_blacklist(),