Sysroot compatibility?

[marekkrk]

I am attempting to build nginx with rules_foreign_cc 0.15.0. I have configured Bazel to use a hermetic C++ toolchain: toolchains_llvm 1.5.0, LLVM 20.1.0 and debian_bullseye_amd64_sysroot.tar.xz. When I attempt to build nginx with configure_make all programs produced by ./configure fail to link with the following error:

/usr/bin/ld: (.text+0x19): undefined reference to `__libc_csu_init'

When I remove the sysroot from C++ toolchain configuration, ./configure works as expected.

What could be the reason of that behaviour? Are rules_foreign_cc hermetic? The libc version in my sysroot is libc-2.31.so.

[marekkrk]

Ok, figured it out. The following parameter needs to be added to to CFLAGS and/or CXXFLAGS:
"-fuse-ld=lld"

It can simply be passed through configure_make.copts.

Rules_foreign_cc only adds it to LDFLAGS in my scenario which I think is a defect, C/C++ compiler uses that parameter to determine which linker to use. Only the linker itself looks at LDFLAGS. Without this parameter my nginx build uses /usr/bin/ld which results in the error I described and also breaks hermeticity of the build.