/tmp $ cat tmp.scm 
(import (scheme base) (scheme write))

(write (map char->integer (string->list
                           (utf8->string
                            #u8(194)))))
(newline)

/tmp $ valgrind -s --track-origins=yes ~/.local/chicken-master/bin/csi -n -s tmp.scm 
==20526== Memcheck, a memory error detector
==20526== Copyright (C) 2002-2024, and GNU GPL'd, by Julian Seward et al.
==20526== Using Valgrind-3.25.1 and LibVEX; rerun with -h for copyright info
==20526== Command: /home/user/.local/chicken-master/bin/csi -n -s tmp.scm
==20526== 
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5145D71: utf8_decode (utf.c:3202)
==20526==    by 0x514906C: C_utf_validate (utf.c:3520)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==  Uninitialised value was created by a stack allocation
==20526==    at 0x5131ED1: allocate_bytevector_2 (runtime.c:10307)
==20526== 
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5145DBE: utf8_decode (utf.c:3204)
==20526==    by 0x514906C: C_utf_validate (utf.c:3520)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==  Uninitialised value was created by a stack allocation
==20526==    at 0x5131ED1: allocate_bytevector_2 (runtime.c:10307)
==20526== 
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5145E77: utf8_decode (utf.c:3212)
==20526==    by 0x514906C: C_utf_validate (utf.c:3520)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526== 
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5149076: C_utf_validate (utf.c:3521)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C07922: f_7619 (eval.c:18529)
==20526== 

Error: (utf8->string) string contains invalid UTF-8 sequence: #u8(194)

	Call history:

	<syntax>	 (##core#quote #f)
	tmp.scm:1	 (##core#require r7lib scheme.write)
	<syntax>	 (chicken.load#load-unit (##core#quote r7lib) (##core#quote #f) (##core#quote #f))
	<syntax>	 (##core#quote r7lib)
	<syntax>	 (##core#quote #f)
	<syntax>	 (##core#quote #f)
	<eval>	 (chicken.load#load-unit (##core#quote library) (##core#quote #f) (##core#quote #f))
	<eval>	 (chicken.load#load-unit (##core#quote r7lib) (##core#quote #f) (##core#quote #f))
	tmp.scm:3	 (write (map char->integer (string->list (utf8->string #u8(194)))))
	tmp.scm:3	 (map char->integer (string->list (utf8->string #u8(194))))
	tmp.scm:3	 (string->list (utf8->string #u8(194)))
	tmp.scm:4	 (utf8->string #u8(194))
	tmp.scm:3	 (write (map char->integer (string->list (utf8->string #u8(194)))))
	tmp.scm:3	 (map char->integer (string->list (utf8->string #u8(194))))
	tmp.scm:3	 (string->list (utf8->string #u8(194)))
	tmp.scm:4	 (utf8->string #u8(194))	<--
==20526== 
==20526== HEAP SUMMARY:
==20526==     in use at exit: 3,358,039 bytes in 4,110 blocks
==20526==   total heap usage: 4,113 allocs, 3 frees, 4,406,639 bytes allocated
==20526== 
==20526== LEAK SUMMARY:
==20526==    definitely lost: 0 bytes in 0 blocks
==20526==    indirectly lost: 0 bytes in 0 blocks
==20526==      possibly lost: 0 bytes in 0 blocks
==20526==    still reachable: 3,358,039 bytes in 4,110 blocks
==20526==         suppressed: 0 bytes in 0 blocks
==20526== Rerun with --leak-check=full to see details of leaked memory
==20526== 
==20526== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)
==20526== 
==20526== 1 errors in context 1 of 4:
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5149076: C_utf_validate (utf.c:3521)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C07922: f_7619 (eval.c:18529)
==20526== 
==20526== 
==20526== 1 errors in context 2 of 4:
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5145E77: utf8_decode (utf.c:3212)
==20526==    by 0x514906C: C_utf_validate (utf.c:3520)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526== 
==20526== 
==20526== 1 errors in context 3 of 4:
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5145DBE: utf8_decode (utf.c:3204)
==20526==    by 0x514906C: C_utf_validate (utf.c:3520)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==  Uninitialised value was created by a stack allocation
==20526==    at 0x5131ED1: allocate_bytevector_2 (runtime.c:10307)
==20526== 
==20526== 
==20526== 1 errors in context 4 of 4:
==20526== Conditional jump or move depends on uninitialised value(s)
==20526==    at 0x5145D71: utf8_decode (utf.c:3202)
==20526==    by 0x514906C: C_utf_validate (utf.c:3520)
==20526==    by 0x4A721E3: f_22866 (library.c:34764)
==20526==    by 0x4A72046: f_22841 (library.c:34747)
==20526==    by 0x4C06C13: f_7588 (eval.c:18418)
==20526==    by 0x4BC9381: f_4236 (eval.c:10185)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==    by 0x4C06AA2: f_7581 (eval.c:18395)
==20526==    by 0x4BC66A5: f_4001 (eval.c:9811)
==20526==    by 0x4C0689E: f_7574 (eval.c:18370)
==20526==  Uninitialised value was created by a stack allocation
==20526==    at 0x5131ED1: allocate_bytevector_2 (runtime.c:10307)
==20526== 
==20526== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)
/tmp $