Why is the cross value set when using the llvm toolchain?

[Doekin]

In xmake/toolchains/llvm/check.lua, the cross, bindir, and sdkdir values are automatically evaluated if they are not explicitly specified:

xmake/xmake/toolchains/llvm/check.lua

Lines 99 to 106 in 8ed7230

	if cross_toolchain then
	toolchain:config_set("cross", cross_toolchain.cross)
	toolchain:config_set("bindir", cross_toolchain.bindir)
	toolchain:config_set("sdkdir", cross_toolchain.sdkdir)
	toolchain:configs_save()
	else
	raise("llvm toolchain not found!")
	end

On Arch Linux, running the following commands:

xmake f -c -vD --toolchain=llvm  
xmake f -c -vD -p cross --cross=aarch64-linux-gnu- --toolchain=llvm  

Produces the following evaluation:

{ 
  cross = "i686-w64-mingw32-",  
  bindir = "/usr/bin",  
  sdkdir = "/usr"  
}

I’m unsure why the cross value is being set to "i686-w64-mingw32-" by default. Could someone explain the reasoning behind this behavior?

[waruqi]

please provide full verbose logs

[Doekin]

The observed behavior is that toolchain:cross() always returns i686-w64-mingw32- during the on_load step, so there are no relevant logs to provide in this case.

I’m currently trying to implement cross-compiling for llvm by

toolchain:add("cxflags", "--target=" .. toolchain:cross())

However, I noticed that toolchain:cross() consistently returns i686-w64-mingw32-, regardless of what I set with --cross=xxx.

[waruqi]

but I need logs

[Doekin]

To help clarify the issue, I applied the following changes to the code:

xmake/xmake/toolchains/llvm/xmake.lua

Lines 63 to 66 in 15ba86c

	elseif toolchain:is_arch("i386", "x86") then
	march = "-m32"
	end
	if march then

        elseif toolchain:is_arch("i386", "x86") then
            march = "-m32"
+        elseif toolchain:is_plat("cross") and toolchain:cross() then
+            march = toolchain:cross():gsub("(.*)%-$", "%1")
+            local sysroot
+            if os.isdir(path.join("/usr", march, "include")) then
+                sysroot = path.join("/usr", march)
+            end
+            if sysroot then
+                toolchain:add("cxflags", "--sysroot=" .. sysroot)
+                toolchain:add("mxflags", "--sysroot=" .. sysroot)
+                toolchain:add("asflags", "--sysroot=" .. sysroot)
+                toolchain:add("ldflags", "--sysroot=" .. sysroot)
+                toolchain:add("shflags", "--sysroot=" .. sysroot)
+            end
+            march = "--target=" .. march
        end
        if march then

Then, I ran the following command:

$ xmake f -c -vD -p cross --cross=aarch64-linux-gnu- --toolchain=llvm
{
    mode = release,
    kind = static,
    buildir = build,
    host = linux,
    mingw = /usr/x86_64-w64-mingw32,
    plat = cross,
    cross = aarch64-linux-gnu-,
    arch = arm64,
    toolchain = llvm,
    diagnosis = true,
    clean = true,
    ccache = true,
}

$ xmake -r -vD hello_c
checking for clang ... /usr/bin/clang
checking for the c compiler (cc) ... clang
checking for /usr/bin/clang ... ok
checking for flags (-fPIC) ... ok
> clang "-fPIC" "-Qunused-arguments" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
checking for flags (-O3) ... ok
> clang "-O3" "-Qunused-arguments" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
checking for flags (-DNDEBUG) ... ok
> clang "-DNDEBUG" "-Qunused-arguments" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
[ 50%]: cache compiling.release src/hello.c
/usr/bin/clang -c -Qunused-arguments --sysroot=/usr/i686-w64-mingw32 --target=i686-w64-mingw32 -fvisibility=hidden -Wall -Wextra -Wpedantic -O3 -DNDEBUG -o build/.objs/hello_c/cross/arm64/release/src/hello.c.o src/hello.c
checking for flags (-MMD -MF) ... ok
> clang "-MMD" "-MF" "/dev/null" "-Qunused-arguments" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
checking for flags (-fdiagnostics-color=always) ... ok
> clang "-fdiagnostics-color=always" "-Qunused-arguments" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
checking for flags (-Wno-gnu-line-marker -Werror) ... ok
> clang "-Wno-gnu-line-marker" "-Werror" "-Qunused-arguments" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
checking for clang++ ... /usr/bin/clang++
checking for the linker (ld) ... clang++
checking for /usr/bin/clang++ ... ok
checking for flags (-fPIC) ... no
> clang++ "-fPIC" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32" "--sysroot=/usr/i686-w64-mingw32" "--target=i686-w64-mingw32"
checkinfo: @programdir/core/sandbox/modules/os.lua:273: /usr/bin/i686-w64-mingw32-ld: cannot find -lgcc: No such file or directory
/usr/bin/i686-w64-mingw32-ld: cannot find -lgcc: No such file or directory
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

stack traceback:
    [C]: in function 'error'
    [@programdir/core/base/os.lua:1075]:
    [@programdir/core/sandbox/modules/os.lua:273]: in function 'runv'
    [@programdir/modules/core/tools/gcc/has_flags.lua:42]:
[ 75%]: linking.release hello_c
/usr/bin/clang++ -o build/cross/arm64/release/hello_c build/.objs/hello_c/cross/arm64/release/src/hello.c.o --sysroot=/usr/i686-w64-mingw32 --target=i686-w64-mingw32 -s
/usr/bin/i686-w64-mingw32-ld: cannot find -lgcc: No such file or directory
/usr/bin/i686-w64-mingw32-ld: cannot find -lgcc: No such file or directory
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
error: @programdir/core/main.lua:329: @programdir/actions/build/main.lua:148: @programdir/modules/async/runjobs.lua:325: @programdir/actions/build/kinds/binary.lua:57: @programdir/core/sandbox/modules/os.lua:378: execv(/usr/bin/clang++ -o build/cross/arm64/release/hello_c build/.objs/hello_c/cross/arm64/release/src/hello.c.o --sysroot=/usr/i686-w64-mingw32 --target=i686-w64-mingw32 -s) failed(1)
stack traceback:
    [C]: in function 'error'
    [@programdir/core/base/os.lua:1075]:
    [@programdir/core/sandbox/modules/os.lua:378]: in function 'execv'
    [@programdir/modules/core/tools/gcc.lua:599]:
    [C]: in function 'xpcall'
    [@programdir/core/base/utils.lua:246]:
    [@programdir/core/tool/linker.lua:232]: in function 'link'
    [@programdir/actions/build/kinds/binary.lua:57]: in function 'callback'
    [@programdir/modules/core/project/depend.lua:227]: in function 'on_changed'
    [@programdir/actions/build/kinds/binary.lua:41]: in function '_do_link_target'
    [@programdir/actions/build/kinds/binary.lua:87]:
    [@programdir/actions/build/kinds/binary.lua:114]: in function '_link_target'
    [@programdir/actions/build/kinds/binary.lua:142]: in function 'jobfunc'
    [@programdir/modules/async/runjobs.lua:241]:
    [C]: in function 'xpcall'
    [@programdir/core/base/utils.lua:246]: in function 'trycall'
    [@programdir/core/sandbox/modules/try.lua:117]: in function 'try'
    [@programdir/modules/async/runjobs.lua:224]: in function 'cotask'
    [@programdir/core/base/scheduler.lua:406]:

It seems that the toolchain:cross() value is not being applied correctly, causing the wrong --sysroot and --target values to be used.

[waruqi]

I don't know, these are only set on mingw platforms.

[Doekin]

I suspect the issue might be that the llvm toolchain is being added as a cross-toolchain but fails to properly use the provided cross option.

While I'm still unsure why using llvm is treated as cross-compiling, the following change seems to act as a workaround:

- local cross_toolchain = find_cross_toolchain(sdkdir, {bindir = bindir})
+ local cross_toolchain = find_cross_toolchain(sdkdir, {bindir = bindir, cross = cross})