Fails to build for ARM: "selected processor lacks an FPU"

[xobs]

Note: This bug is for backtrace-sys, however I'm unable to locate that repository -- the page at https://crates.io/crates/backtrace-sys links to here.

When attempting to build backtrace-rs for arm7-unknown-linux-musleabi, I get the error cargo:warning=cc1.exe: error: '-mfloat-abi=hard': selected processor lacks an FPU.

Full cargo output:

❯ cargo build --target=armv7-unknown-linux-musleabihf
   Compiling cc v1.0.42
   Compiling rustc-demangle v0.1.16
   Compiling libusb-sys v0.2.5 (D:\Code\Fomu\wishbone-adapter\wishbone-tool\libusb-sys)
   Compiling backtrace-sys v0.1.31
error: failed to run custom build command for `backtrace-sys v0.1.31`

Caused by:
  process didn't exit successfully: `D:\Code\Fomu\wishbone-adapter\wishbone-tool\target\debug\build\backtrace-sys-518864e4e1eb0544\build-script-build` (exit code: 1)
--- stdout
cargo:rustc-cfg=rbt
TARGET = Some("armv7-unknown-linux-musleabihf")
OPT_LEVEL = Some("0")
HOST = Some("x86_64-pc-windows-msvc")
CC_armv7-unknown-linux-musleabihf = None
CC_armv7_unknown_linux_musleabihf = None
TARGET_CC = None
CC = Some("arm-linux-musleabihf-gcc")
CFLAGS_armv7-unknown-linux-musleabihf = None
CFLAGS_armv7_unknown_linux_musleabihf = None
TARGET_CFLAGS = None
CFLAGS = None
CRATE_CC_NO_DEFAULTS = None
CARGO_CFG_TARGET_FEATURE = Some("crt-static")
running: "arm-linux-musleabihf-gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-static" "-march=armv7-a" "-I" "src/libbacktrace" "-I" "D:\\Code\\Fomu\\wishbone-adapter\\wishbone-tool\\target\\armv7-unknown-linux-musleabihf\\debug\\build\\backtrace-sys-8a0e27e4d3390088\\out" "-fvisibility=hidden" "-DBACKTRACE_ELF_SIZE=32" "-DBACKTRACE_SUPPORTED=1" "-DBACKTRACE_USES_MALLOC=1" "-DBACKTRACE_SUPPORTS_THREADS=0" "-DBACKTRACE_SUPPORTS_DATA=0" "-DHAVE_DL_ITERATE_PHDR=1" "-D_GNU_SOURCE=1" "-D_LARGE_FILES=1" "-Dbacktrace_full=__rbt_backtrace_full" "-Dbacktrace_dwarf_add=__rbt_backtrace_dwarf_add" "-Dbacktrace_initialize=__rbt_backtrace_initialize" "-Dbacktrace_pcinfo=__rbt_backtrace_pcinfo" "-Dbacktrace_syminfo=__rbt_backtrace_syminfo" "-Dbacktrace_get_view=__rbt_backtrace_get_view" "-Dbacktrace_release_view=__rbt_backtrace_release_view" "-Dbacktrace_alloc=__rbt_backtrace_alloc" "-Dbacktrace_free=__rbt_backtrace_free" "-Dbacktrace_vector_finish=__rbt_backtrace_vector_finish" "-Dbacktrace_vector_grow=__rbt_backtrace_vector_grow" "-Dbacktrace_vector_release=__rbt_backtrace_vector_release" "-Dbacktrace_close=__rbt_backtrace_close" "-Dbacktrace_open=__rbt_backtrace_open" "-Dbacktrace_print=__rbt_backtrace_print" "-Dbacktrace_simple=__rbt_backtrace_simple" "-Dbacktrace_qsort=__rbt_backtrace_qsort" "-Dbacktrace_create_state=__rbt_backtrace_create_state" "-Dbacktrace_uncompress_zdebug=__rbt_backtrace_uncompress_zdebug" "-Dmacho_get_view=__rbt_macho_get_view" "-Dmacho_symbol_type_relevant=__rbt_macho_symbol_type_relevant" "-Dmacho_get_commands=__rbt_macho_get_commands" "-Dmacho_try_dsym=__rbt_macho_try_dsym" "-Dmacho_try_dwarf=__rbt_macho_try_dwarf" "-Dmacho_get_addr_range=__rbt_macho_get_addr_range" "-Dmacho_get_uuid=__rbt_macho_get_uuid" "-Dmacho_add=__rbt_macho_add" "-Dmacho_add_symtab=__rbt_macho_add_symtab" "-Dmacho_file_to_host_u64=__rbt_macho_file_to_host_u64" "-Dmacho_file_to_host_u32=__rbt_macho_file_to_host_u32" "-Dmacho_file_to_host_u16=__rbt_macho_file_to_host_u16" "-o" "D:\\Code\\Fomu\\wishbone-adapter\\wishbone-tool\\target\\armv7-unknown-linux-musleabihf\\debug\\build\\backtrace-sys-8a0e27e4d3390088\\out\\src/libbacktrace\\alloc.o" "-c" "src/libbacktrace/alloc.c"
cargo:warning=cc1.exe: error: '-mfloat-abi=hard': selected processor lacks an FPU
exit code: 1

--- stderr


error occurred: Command "arm-linux-musleabihf-gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-static" "-march=armv7-a" "-I" "src/libbacktrace" "-I" "D:\\Code\\Fomu\\wishbone-adapter\\wishbone-tool\\target\\armv7-unknown-linux-musleabihf\\debug\\build\\backtrace-sys-8a0e27e4d3390088\\out" "-fvisibility=hidden" "-DBACKTRACE_ELF_SIZE=32" "-DBACKTRACE_SUPPORTED=1" "-DBACKTRACE_USES_MALLOC=1" "-DBACKTRACE_SUPPORTS_THREADS=0" "-DBACKTRACE_SUPPORTS_DATA=0" "-DHAVE_DL_ITERATE_PHDR=1" "-D_GNU_SOURCE=1" "-D_LARGE_FILES=1" "-Dbacktrace_full=__rbt_backtrace_full" "-Dbacktrace_dwarf_add=__rbt_backtrace_dwarf_add" "-Dbacktrace_initialize=__rbt_backtrace_initialize" "-Dbacktrace_pcinfo=__rbt_backtrace_pcinfo" "-Dbacktrace_syminfo=__rbt_backtrace_syminfo" "-Dbacktrace_get_view=__rbt_backtrace_get_view" "-Dbacktrace_release_view=__rbt_backtrace_release_view" "-Dbacktrace_alloc=__rbt_backtrace_alloc" "-Dbacktrace_free=__rbt_backtrace_free" "-Dbacktrace_vector_finish=__rbt_backtrace_vector_finish" "-Dbacktrace_vector_grow=__rbt_backtrace_vector_grow" "-Dbacktrace_vector_release=__rbt_backtrace_vector_release" "-Dbacktrace_close=__rbt_backtrace_close" "-Dbacktrace_open=__rbt_backtrace_open" "-Dbacktrace_print=__rbt_backtrace_print" "-Dbacktrace_simple=__rbt_backtrace_simple" "-Dbacktrace_qsort=__rbt_backtrace_qsort" "-Dbacktrace_create_state=__rbt_backtrace_create_state" "-Dbacktrace_uncompress_zdebug=__rbt_backtrace_uncompress_zdebug" "-Dmacho_get_view=__rbt_macho_get_view" "-Dmacho_symbol_type_relevant=__rbt_macho_symbol_type_relevant" "-Dmacho_get_commands=__rbt_macho_get_commands" "-Dmacho_try_dsym=__rbt_macho_try_dsym" "-Dmacho_try_dwarf=__rbt_macho_try_dwarf" "-Dmacho_get_addr_range=__rbt_macho_get_addr_range" "-Dmacho_get_uuid=__rbt_macho_get_uuid" "-Dmacho_add=__rbt_macho_add" "-Dmacho_add_symtab=__rbt_macho_add_symtab" "-Dmacho_file_to_host_u64=__rbt_macho_file_to_host_u64" "-Dmacho_file_to_host_u32=__rbt_macho_file_to_host_u32" "-Dmacho_file_to_host_u16=__rbt_macho_file_to_host_u16" "-o" "D:\\Code\\Fomu\\wishbone-adapter\\wishbone-tool\\target\\armv7-unknown-linux-musleabihf\\debug\\build\\backtrace-sys-8a0e27e4d3390088\\out\\src/libbacktrace\\alloc.o" "-c" "src/libbacktrace/alloc.c" with args "arm-linux-musleabihf-gcc" did not execute successfully (status code exit code: 1).



warning: build failed, waiting for other jobs to finish...
error: build failed
❯ 

Note that it is attempting to build with -march=armv7-a and -mfloat-abi=hard. It seems that as of https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=262556 the armv7-a target no longer includes an FPU by default, and instead you need to specify -march=armv7-a+fp.

I am able to compile other software using build.rs where I have added the following to build.rs:

	if target_os == "linux" {
		if target_triple == "armv7-unknown-linux-musleabihf" {
			base_config.flag("-mfpu=neon");
		}
        }

[xobs]

Ah, the backtrace-sys crate is in the crates directory.

The following patch fixes the build for me:

diff --git a/crates/backtrace-sys/build.rs b/crates/backtrace-sys/build.rs
index 9e4dff5..985d4c8 100644
--- a/crates/backtrace-sys/build.rs
+++ b/crates/backtrace-sys/build.rs
@@ -43,6 +43,10 @@ fn main() {
     } else {
         build.file("src/libbacktrace/elf.c");

+        if target == "armv7-unknown-linux-musleabihf" {
+            build.flag("-mfpu=neon");
+        }
+
         let pointer_width = env::var("CARGO_CFG_TARGET_POINTER_WIDTH").unwrap();
         if pointer_width == "64" {
             build.define("BACKTRACE_ELF_SIZE", "64");

[alexcrichton]

Thanks for the report! I think this will want to be fixed at https://github.com/alexcrichton/cc-rs which is where flags are sourced from, and PRs would be most welcome there!

[patrickelectric]

Can a version with this fix be released ?

[alexcrichton]

Sure thing, published!

[ZoeyR]

@alexcrichton this still seems to be happening as of cc-rs 1.0.50