Here I see uninteresting things like:

--8<---------------cut here---------------start------------->8---
scm_c_shrink_bytevector 32768 -> 6960
new_bv = 0x1e96000, bv = 0x1e9a000
importing path `/gnu/store/5nhsz368f88bbgkjjwzz5k24nnnrk544-coreutils-8.22.drv'

;;; (import ("/gnu/store/5nhsz368f88bbgkjjwzz5k24nnnrk544-coreutils-8.22.drv"))
scm_c_shrink_bytevector 32768 -> 6960
new_bv = 0x1efb000, bv = 0x1eff000

;;; (import ())
attach GDB to 10124
--8<---------------cut here---------------end--------------->8---

Then I can call GC_default_print_heap_obj_proc(0x1efb000) from GDB,
which displays:

--8<---------------cut here---------------start------------->8---
object at 0x1efb000 of appr. 6992 bytes (atomic)
--8<---------------cut here---------------end--------------->8---

IOW, everything looks alright, except that the contents of new_bv really
are corrupt.

Ludo’.