pico-blink Build Error

[star-light-1]

When trying to build the pico-blink example on macOS with:

cd swift-embedded-examples/pico-blink
rm -rf .build ; TOOLCHAINS=org.swift.59202404131a ./build.sh

I get the following error:

# Link
$CLANG .build/release/Support.build/{Support.c,crt0.S}.o .build/release/Blinky.build/*.o -target armv6m-apple-none-macho -o $BUILDROOT/blinky $LD_FLAGS
+ /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-04-13-a.xctoolchain/usr/bin/clang .build/release/Support.build/Support.c.o .build/release/Support.build/crt0.S.o .build/release/Blinky.build/Blinky.swift.o -target armv6m-apple-none-macho -o /path/to/swift-embedded-examples/pico-blink/.build/armv6m-apple-none-macho/release/blinky -static -Wl,-e,_reset -dead_strip -Wl,-no_zero_fill_sections -Wl,-segalign,4 -Wl,-segaddr,__RESET,0x20000000 -Wl,-segaddr,__VECTORS,0x20000100 -Wl,-seg1addr,0x20000200 -Wl,-pagezero_size,0 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/lib/darwin/macho_embedded/libclang_rt.soft_static.a
ld: warning: ignoring file /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-04-13-a.xctoolchain/usr/lib/clang/17/lib/darwin/macho_embedded/libclang_rt.soft_static.a, building for free standing-armv6m but attempting to link with file built for macOS-armv7
ld: warning: ignoring file /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/lib/darwin/macho_embedded/libclang_rt.soft_static.a, building for free standing-armv6m but attempting to link with file built for macOS-armv7
Undefined symbols for architecture armv6m:
  "___muldi3", referenced from:
      _$s6Blinky4MainV5delayyySiFZTf4nd_n in Blinky.swift.o
ld: symbol(s) not found for architecture armv6m
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Is the ___muldi3 symbol not available on armv6m? If not, why is it being used?

System information:

swift-DEVELOPMENT-SNAPSHOT-2024-04-13-a.xctoolchain
Apple Swift version 6.0-dev (LLVM 01231f56c62f4c4, Swift abaa63821080b92)
Darwin Kernel Version 23.4.0: Fri Mar 15 00:12:25 PDT 2024; root:xnu-10063.101.17~1

Toolchain ID:

$ plutil -extract CFBundleIdentifier raw -o - /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-*.xctoolchain/Info.plist                                    
org.swift.59202404131a

Git commit of swift-embedded-examples:

69dc23e718c5b20797daec17d4754cd42bb21c24

Full build log: pico-blink-build-log.txt

[Joannis]

@star-light-1 ___muldi3 multiplies two integers. The 100 * N is where multiplication is used in func delay(_ N: Int)

[Joannis]

Try using the toolchain from April 3rd, that worked for me.

[star-light-1]

The oldest toolchain I could find in section "Trunk Development (main)" on swift.org/download is April 4, 2024, which for me produces the same error shown above.
Latest toolchain of the 5.10 branch produces:

error: unable to load standard library for target 'armv6m-apple-none-macho'

[kubamracek]

I can sort-of reproduce the problem. One issue is that this part of the build script for pico-blink should not be necessary anymore, as the expectation is that the downloadable swift.org toolchain includes a valid libclang_rt.soft_static.a for the CPU arch we're building here (armv6m):

XCODE_RESOURCE_DIR=`env TOOLCHAINS="" xcrun clang -print-resource-dir`
LD_FLAGS+=" $XCODE_RESOURCE_DIR/lib/darwin/macho_embedded/libclang_rt.soft_static.a"

Once I drop this, I get:

# Link
$CLANG .build/release/Support.build/{Support.c,crt0.S}.o .build/release/Blinky.build/*.o -target armv6m-apple-none-macho -o $BUILDROOT/blinky $LD_FLAGS
+ /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-04-25-a.xctoolchain/usr/bin/clang .build/release/Support.build/Support.c.o .build/release/Support.build/crt0.S.o .build/release/Blinky.build/Blinky.swift.o -target armv6m-apple-none-macho -o /Users/kuba/Documents/swift-embedded-examples/pico-blink/.build/armv6m-apple-none-macho/release/blinky -static -Wl,-e,_reset -dead_strip -Wl,-no_zero_fill_sections -Wl,-segalign,4 -Wl,-segaddr,__RESET,0x20000000 -Wl,-segaddr,__VECTORS,0x20000100 -Wl,-seg1addr,0x20000200 -Wl,-pagezero_size,0
ld: warning: ignoring file /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-04-25-a.xctoolchain/usr/lib/clang/17/lib/darwin/macho_embedded/libclang_rt.soft_static.a, building for free standing-armv6m but attempting to link with file built for macOS-armv7
Undefined symbols for architecture armv6m:
  "___muldi3", referenced from:
      _$s6Blinky4MainV5delayyySiFZTf4nd_n in Blinky.swift.o
ld: symbol(s) not found for architecture armv6m

The problem is that libclang_rt.soft_static.a is somehow only armv7 and contains no other slices. That will need to be fixed, but I'm not sure how that happens in the first place.

The only workaround I can think of (short of actually removing the multiplication from source code, but sometimes those are really useful 😄) would be to rebuild libclang_rt from LLVM's compiler-rt from source and explicitly build the armv6m slice, and link that instead.

[kubamracek]

@star-light-1 can I also ask which Xcode version are you using?

[star-light-1]

This happend using Xcode 15.3 (15E204a)

[Bauer312]

The most recent 5.10 (May 1, 2024) and 6.0 (April 30, 2024) snapshot both still produce the linker warning
ld: warning: ignoring file /<SNIP>/macho_embedded/libclang_rt.soft_static.a, building for free standing-armv6m but attempting to link with file built for macOS-armv7

5.10 fails with the undefined symbol, while 6.0 continues and produces the expected blinky.uf2 output, although not in the location that the README says it will appear. I have a pico w and it appears to reject loading it, but I need to do more testing to see if this is unrelated.