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t: avoid perl's pack/unpack "Q" specifier

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The perl script introduced by 86b008ee61 (t: add library for munging
chunk-format files, 2023-10-09) uses pack("Q") and unpack("Q") to read
and write 64-bit values ("quadwords" in perl parlance) from the on-disk
chunk files. However, some builds of perl may not support 64-bit
integers at all, and throw an exception here. While some 32-bit
platforms may still support 64-bit integers in perl (such as our linux32
CI environment), others reportedly don't (the NonStop 32-bit builds).

We can work around this by treating the 64-bit values as two 32-bit
values. We can't ever combine them into a single 64-bit value, but in
practice this is OK. These are representing file offsets, and our files
are much smaller than 4GB. So the upper half of the 64-bit value will
always be 0.

We can just introduce a few helper functions which perform the
translation and double-check our assumptions.

Reported-by: Randall S. Becker <randall.becker@nexbridge.ca>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2023-11-03 12:20:19 -04:00 committed by Junio C Hamano
parent 7538f9d89b
commit 4815c3c4b2
1 changed files with 27 additions and 3 deletions
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30
t/lib-chunk/corrupt-chunk-file.pl
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@ -21,6 +21,30 @@ sub copy {
return $buf;
}
# Some platforms' perl builds don't support 64-bit integers, and hence do not
# allow packing/unpacking quadwords with "Q". The chunk format uses 64-bit file
# offsets to support files of any size, but in practice our test suite will
# only use small files. So we can fake it by asking for two 32-bit values and
# discarding the first (most significant) one, which is equivalent as long as
# it's just zero.
sub unpack_quad {
my $bytes = shift;
my ($n1, $n2) = unpack("NN", $bytes);
die "quad value exceeds 32 bits" if $n1;
return $n2;
}
sub pack_quad {
my $n = shift;
my $ret = pack("NN", 0, $n);
# double check that our original $n did not exceed the 32-bit limit.
# This is presumably impossible on a 32-bit system (which would have
# truncated much earlier), but would still alert us on a 64-bit build
# of a new test that would fail on a 32-bit build (though we'd
# presumably see the die() from unpack_quad() in such a case).
die "quad round-trip failed" if unpack_quad($ret) != $n;
return $ret;
}
# read until we find table-of-contents entry for chunk;
# note that we cheat a bit by assuming 4-byte alignment and
# that no ToC entry will accidentally look like a header.
@ -28,7 +52,7 @@ sub copy {
# If we don't find the entry, copy() will hit EOF and exit
# (which should cause the caller to fail the test).
while (copy(4) ne $chunk) { }
my $offset = unpack("Q>", copy(8));
my $offset = unpack_quad(copy(8));
# In clear mode, our length will change. So figure out
# the length by comparing to the offset of the next chunk, and
@ -38,11 +62,11 @@ sub copy {
my $id;
do {
$id = copy(4);
my $next = unpack("Q>", get(8));
my $next = unpack_quad(get(8));
if (!defined $len) {
$len = $next - $offset;
}
print pack("Q>", $next - $len + length($bytes));
print pack_quad($next - $len + length($bytes));
} while (unpack("N", $id));
}