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Document remote protocol pid and thread id sizes

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The recent ptid work came from a bug where a problem was observed due
to sign extension.  That bug also suggested documenting the guaranteed
range of thread- and process-ids in the remote protocol.

This patch documents these as being 32-bit values at minimum.  I also
added static asserts to ensure this is true -- note that although
'int' may be 16 bit per the C standard, I doubt gdb would build on
such a host.

I didn't specify a maximum because it is host-dependent.  This is
perhaps something to change, and while I do have some work in this
area, it's quite invasive.  Also, while widening the range here would
be good, it would also be incompatible in a sense, where a newer
protocol implementation may end up using values not supported by older
versions of gdb.  Perhaps one idea would be to simply change these
both to int32_t and move on.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33979
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
This commit is contained in:
Tom Tromey 2026-07-02 13:32:25 -06:00
parent a4481c8ff8
commit e88bc211ae
2 changed files with 11 additions and 4 deletions
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11
gdb/doc/gdb.texinfo
View file

@ -43463,7 +43463,8 @@ Several packets and replies include a @var{thread-id} field to identify
a thread. Normally these are positive numbers with a target-specific
interpretation, formatted as big-endian hex strings. A @var{thread-id}
can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
pick any thread.
pick any thread. @value{GDBN} guarantees that values of up to 32 bits
will work here.
In addition, the remote protocol supports a multiprocess feature in
which the @var{thread-id} syntax is extended to optionally include both
@ -43475,9 +43476,11 @@ to indicate all processes or threads (respectively), or @samp{0} to
indicate an arbitrary process or thread. Specifying just a process, as
@samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
error to specify all processes but a specific thread, such as
@samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
for those packets and replies explicitly documented to include a process
ID, rather than a @var{thread-id}.
@samp{p-1.@var{tid}}. @value{GDBN} guarantees that values of up to 32
bits will work for both @var{pid} and @var{tid}. Note that the
@samp{p} prefix is @emph{not} used for those packets and replies
explicitly documented to include a process ID, rather than a
@var{thread-id}.
The multiprocess @var{thread-id} syntax extensions are only used if both
@value{GDBN} and the stub report support for the @samp{multiprocess}

4
gdbsupport/ptid.h
View file

@ -44,6 +44,10 @@ public:
using lwp_type = long;
using tid_type = ULONGEST;
/* These limits are documented in the manual. */
static_assert (sizeof (pid_type) >= 4);
static_assert (sizeof (lwp_type) >= 4);
/* Must have a trivial defaulted default constructor so that the
type remains POD. */
ptid_t () noexcept = default;