During my work porting MS-DOS v4.01's msdos kernel module I came across an error. When something is assembled into a section (anything, eg "nop") then a label is defined and afterwards the same label is declared EXTERN, NASM emits an error. Note that when the label is defined as EXTERN first, then defined, and then declared EXTERN again it works. Not assembling anything into the current section before the label line also seems to avoid the error, but is obviously not a useful workaround.

Test cases:

test$ nasm -v
NASM version 2.16.02rc2 compiled on Oct 12 2023
test$ cat test1.asm
nop
label:
extern label
test$ cat test2.asm
nop
extern label
label:
extern label
test$ cat test3.asm
label:
extern label
test$ nasm -f obj test1.asm
test1.asm:3: error: label `label' inconsistently redefined
test1.asm:2: info: label `label' originally defined here
test$ nasm -f obj test2.asm
test$ nasm -f obj test3.asm
test$