This can be reproduced by getting the read() above 2G, which induces a short read, thus triggering the erroneous failure.
$ truncate -s 5G 5G $ cat 5G | TMPDIR=$PWD tac | wc -c tac: /tmp/tacFt7txA: read error: Illegal seek 0 With the fix in place we now get: $ cat 5G | TMPDIR=$PWD src/tac | wc -c 5368709120 * src/tac.c (tac_seekable): Use full_read() to handle short reads. * NEWS: Mention the bug fix. Reported at https://bugs.debian.org/1042546 --- NEWS | 4 ++++ src/tac.c | 3 ++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/NEWS b/NEWS index 92e591ee2..011058299 100644 --- a/NEWS +++ b/NEWS @@ -46,6 +46,10 @@ GNU coreutils NEWS -*- outline -*- 'pr --length=1 --double-space' no longer enters an infinite loop. [This bug was present in "the beginning".] + tac now handles short reads on its input. Previously it may have exited + erroneously, especially with large input files with no separators. + [This bug was present in "the beginning".] + 'wc -l' and 'cksum' no longer crash with an "Illegal instruction" error on x86 Linux kernels that disable XSAVE YMM. This was seen on Xen VMs. [bug introduced in coreutils-9.0] diff --git a/src/tac.c b/src/tac.c index 285f99a74..4c3655895 100644 --- a/src/tac.c +++ b/src/tac.c @@ -44,6 +44,7 @@ tac -r -s '.\| #include <regex.h> #include "filenamecat.h" +#include "full-read.h" #include "safe-read.h" #include "temp-stream.h" #include "xbinary-io.h" @@ -336,7 +337,7 @@ tac_seekable (int input_fd, char const *file, off_t file_pos) else match_start = past_end; - if (safe_read (input_fd, G_buffer, read_size) != read_size) + if (full_read (input_fd, G_buffer, read_size) != read_size) { error (0, errno, _("%s: read error"), quotef (file)); return false; -- 2.41.0
