Description
lld contains the comment
// The GNU linker uses .note.GNU-stack section as a marker indicating
// that the code in the object file does not expect that the stack is
// executable (in terms of NX bit). If all input files have the marker,
// the GNU linker adds a PT_GNU_STACK segment to tells the loader to
// make the stack non-executable. Most object files have this section as
// of 2017.
This is not entirely correct -- the presence of .note.GNU-stack does not necessarily indicate that the object file is compatible with non-exec stack. That is indeed the most common case, but the note actually indicates the object's expected stack protection -- it may have an X flag to indicate an object file that requires executable stack. See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=278939 for the FreeBSD issue that prompted this.
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
...
[14] .note.GNU-stack PROGBITS 0000000000000000 0077d8 000000 00 X 0 0 1
Executable stacks should be exceedingly rare and I have no issue with requiring an explicit -z execstack, but I think we should at least produce an error if there's a .note.GNU-stack that specifies exec stack and -z execstack is not specified. We should not silently produce broken output.