Search notes:

/usr/lib/crt1.o

This object file contains the _start entry point which bootstraps execution of a program (and eventually calls main()).
The GNU lib c defines it in sysdeps/x86_64/elf/start.S.

See also

/usr/lib/crtn.o
Compare with the Windows CRT startup code in crt0.c
main()
gcc -nostdlib
Apparently, crt1.o is sometimes also found under /usr/lib/x86_64-linux-gnu.
/usr/lib

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