[Q] Bit field/array/pointer output formatting disambiguation

[enh]

On Tue, Oct 16, 2018 at 9:13 PM Eugene Syromyatnikov <evgsyr at gmail.com> wrote:
>
> Hello.
>
> There are some questions about strace users' preference regarding
> formatting of bit fields, arrays, and pointers in strace's output. As
> of now, square brackets are used for designating all these things,
> with the only difference in a separator used for delimiting items in
> arrays and bit masks (a combination of comma and space is used for
> delimiting array items, and a space is used for bit fields). Examples
> from strace(1):
>            getgroups(32, [100, 0]) = 2
>            sigprocmask(SIG_BLOCK, [CHLD TTOU], []) = 0
>
> A special case of an array is a pointer reference, which is also
> printed using square brackets:
>            futex([0x2] /* 0x7fbf7bd730c8 */, FUTEX_WAKE_PRIVATE, 2147483647) = 0
>
> The issue is that an array that contains only a single item may be
> confused with a bit mask that has only one bit set.

does this actually confuse anyone in practice though? i'd honestly not
noticed that they used the same syntax.

> As a solution to
> this, it is proposed to add spaces around elements in bit mask output:
>            getgroups(32, [100]) = 2
>            getgroups(32, []) = 2
>            sigprocmask(SIG_BLOCK, [ CHLD ], [  ]) = 0
>            sigprocmask(SIG_UNBLOCK, ~[  ], NULL) = 0
>
> The main problem associated with that change is that It breaks
> established output formatting rules that are likely being relied upon
> by some. Other significant problem is within the fact that such kind
> of output formatting is somewhat unorthodox (having syntactically
> significant whitespace).
>
> The other slightly relevant issue is that, as of now, there is no
> distinction in the formatting of structures that are referenced by
> pointer compared to embedded structures (e.g., no difference of fields
> A and B in the output of the following structure: struct { struct
> timespec *A; struct timespec B; };); it is proposed to print square
> brackets around structures that are referenced by pointer, and the
> issue is the same: it will change a lot of exiting output and likely
> will break a lot of assumptions.
>
> The solution I can see is to add an option that enables more regular
> output, but that would be yet another option some have to pass for
> each interactive strace session,

yeah, it's bad enough having to remember to pass -x to get hex rather
than octal in 2018... :-(

> and will create the need to have
> significant amount of code for handling both legacy and regular output
> formatting, which doesn't really help maintainability of the project.
>
> So, maybe someone has any ideas in this regard (a completely different
> syntax for bit sets that considers the fact that there are stripped
> prefixes for bit constants, for example)?

i'm assuming you mean saying VM and THREAD rather than CLONE_VM and
CLONE_THREAD? i usually find that trying to be clever like that just
irritates me by making it harder to search (because i'm so used to
typing CLONE_ or whatever).

> --
> Eugene Syromyatnikov
> mailto:evgsyr at gmail.com
> xmpp:esyr at jabber.{ru|org}
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