At last give attempt up to crack clue for "poem" (7)
I believe the answer is:
eclogue
'poem' is the definition.
(I've seen this before)
'at last give attempt up to crack clue' is the wordplay.
'at last' suggests the final letters.
'attempt' becomes 'go' (go is a kind of attempt).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'to crack' means one lot of letters goes inside another (inserted letters crack into others).
The last letter of 'give' is 'e'.
'go' back-to-front is 'og'.
'og' inserted inside 'clue' is 'clogue'.
'e'+'clogue'='ECLOGUE'
'for' is the link.
(Other definitions for eclogue that I've seen before include "country-specific text" , "Work on farm" , "Bucolic" , "pastoral work" , "Poem about country" .)