From: Peter Kaestle
> Sent: 08 November 2024 14:02
>
> The following commit broke dumping unsigned on big endian:
> 34751d8bf (libbb/dump: correct handling of 1-byte signed int format,
> 2023-05-26)
>
> Example of the bug:
>
> root@fct:~ >echo -ne "\xfe\xfd\xfc\xfb" > /tmp/testfile
>
> before 34751d8bf:
> $>/tmp/busybox_1_36_1 hexdump /tmp/testfile
> 0000000 fefd fcfb
> 0000004
>
> with 34751d8bf:
> $>busybox_1_37_0 hexdump /tmp/testfile
> 0000000 fefd00fe fcfb00fc
> 0000004
>
> Problem originated from loading data into 32-bit "value" variable and
> then doing the memcpy of 2 or 4 bytes into value afterwards, without
> taking care of the byte order in case of big-endian cpus.
>
> Replicating same solution used in F_INT with the union fixes the issue.
I'd suggest getting rid of move_from_unaligned16/32() and replacing
with something that just returns the value.
Then the clauses are just:
case 2:
value = read_unaligned_u16(bp);
break;
and nothing will go wrong.
The code will be much smaller as well.
on x86 the above is just *(unsigned short *)bp rather than something
that (I suspect) call memcpy().
David
>
> Signed-off-by: Peter Kaestle <[email protected]>
> ---
> libbb/dump.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/libbb/dump.c b/libbb/dump.c
> index b406a2428..87180dff5 100644
> --- a/libbb/dump.c
> +++ b/libbb/dump.c
> @@ -665,15 +665,23 @@ static NOINLINE void display(priv_dumper_t* dumper)
> conv_u(pr, bp);
> break;
> case F_UINT: {
> + union {
> + uint16_t val16;
> + uint32_t val32;
> + uint64_t val64;
> + } u;
> unsigned value =
> (unsigned char)*bp;
> +
> switch (pr->bcnt) {
> case 1:
> break;
> case 2:
> -
> move_from_unaligned16(value, bp);
> +
> move_from_unaligned16(u.val16, bp);
> + value = u.val16;
> break;
> case 4:
> -
> move_from_unaligned32(value, bp);
> +
> move_from_unaligned32(u.val32, bp);
> + value = u.val32;
> break;
> /* case 8: no users yet
> */
> }
> --
> 2.35.7
>
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