1) Install kernel headers into empty directory 2) Install glibc headers (and "touch" "<sysroot>/usr/include/gnu/stubs.h") 3) Install LLVM runtime builtins 4) Build glibc against sysroot
``` /<pathTo>/toolchain/bin/clang -shared -static-libgcc -Wl,-O1 -Wl,-z,defs -Wl,-dynamic-linker=/lib64/ld-linux-x86-64.so.2 -Wl,-z,pack-relative-relocs -B/<pathTo>/build/csu/ -Wl,--version-script=/<pathTo>/build/libm.map -Wl,--undefined-version -Wl,-soname=libm.so.6 -Wl,-z,relro -Wl,-z,now -L/<pathTo>/build -L/<pathTo>/build/math -L/<pathTo>/build/elf -L/<pathTo>/build/dlfcn -L/<pathTo>/build/nss -L/<pathTo>/build/nis -L/<pathTo>/build/rt -L/<pathTo>/build/resolv -L/<pathTo>/build/mathvec -L/<pathTo>/build/support -L/<pathTo>/build/misc -L/<pathTo>/build/debug -L/<pathTo>/build/nptl -Wl,-rpath-link=/<pathTo>/build:/<pathTo>/build/math:/<pathTo>/build/elf:/<pathTo>/build/dlfcn:/<pathTo>/build/nss:/<pathTo>/build/nis:/<pathTo>/build/rt:/<pathTo>/build/resolv:/<pathTo>/build/mathvec:/<pathTo>/build/support:/<pathTo>/build/misc:/<pathTo>/build/debug:/<pathTo>/build/nptl -o /<pathTo>/build/math/libm.so /<pathTo>/build/csu/abi-note.o -Wl,--whole-archive /<pathTo>/build/math/libm_pic.a -Wl,--no-whole-archive -Wl,--start-group /<pathTo>/build/libc.so /<pathTo>/build/libc_nonshared.a -Wl,--as-needed /<pathTo>/build/elf/ld.so -Wl,--no-as-needed -Wl,--end-group ld.lld: warning: attempt to reassign symbol 'exp2l' of version 'GLIBC_2.2.5' to version 'GLIBC_2.4' ld.lld: error: undefined symbol: __sfp_handle_exceptions >>> referenced by e_sqrtf128.c >>> e_sqrtf128.os:(__ieee754_sqrtf128) in archive >>> /<pathTo>/build/math/libm_pic.a clang: error: linker command failed with exit code 1 ``` I also found it odd that even though I set "LDFLAGS" to include sysroot and "-v", it didn't produce ld.lld verbose output (only clang). It does with other projects. My CFLAGS were included in "config.make", but no LDFLAGS. I was trying to think where I've seen "undefined symbol" before and just now remembered it was when I stripped binaries for musl and ended up finding out the entry "_start" was ripped out. That doesn't apply here I don't think, as no install even happened yet. I see other "attempt to reassign symbol" warnings and read about using "-Wl,--undefined-version" to LDFLAGS, but that didn't make any difference (not sure why it would since they aren't "undefined"). A search led me to https://inbox.sourceware.org/glibc-cvs/?t=20240410130446 with some "sfp" related stuff. I don't know when `sysdeps/x86_64/configure` ends up occurring.
