Re: PATCH: Report libpq version and configuration
| От | Craig Ringer |
|---|---|
| Тема | Re: PATCH: Report libpq version and configuration |
| Дата | |
| Msg-id | CAGRY4ny3or8T9ny3EE85ZvuyxpwASa8af9SzODtgAbqQi4qTaQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: PATCH: Report libpq version and configuration (Alvaro Herrera <alvherre@alvh.no-ip.org>) |
| Список | pgsql-hackers |
On Tue, Oct 27, 2020 at 12:41 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
On 2020-Oct-26, Craig Ringer wrote:
> Patch 0001 adds PQlibInfo(), which returns an array of key/value
> description items reporting on configuration like the full version string,
> SSL support, gssapi support, thread safety, default port and default unix
> socket path. This is for application use and application diagnostics. It
> also adds PQlibInfoPrint() which dumps PQlibInfo() keys/values to stdout.
> See the commit message in patch 0001 for details.
Sounds useful. I'd have PQlibInfoPrint(FILE *) instead, so you can pass
stdout or whichever fd you want.
The decision not to do so was deliberate. On any platform where a shared library could be linked to a different C runtime library than the main executable or other libraries it is not safe to pass a FILE*. This is most common on Windows.
I figured it's just a trivial wrapper anyway, so people can just write or copy it if they really care.
> Patch 0002 exposes LIBPQ_VERSION_STR, LIBPQ_VERSION_NUM and
> LIBPQ_CONFIGURE_ARGS symbols in the dynamic symbol table. These can be
> accessed by a debugger even when the library cannot be loaded or executed,
> and unlike macros are available even in a stripped executable. So they can
> be used to identify a libpq binary found in the wild. Their storage is
> shared with PQlibInfo()'s static data, so they only cost three symbol table
> entries.
Interesting. Is this real-world useful? I'm thinking most of the time
I'd just run the library, but maybe you know of cases where that doesn't
work?
It was prompted by a support conversation about how to identify a libpq. So I'd say yes.
In that case the eventual approach used was to use Python's ctypes to dynamically load libpq then call PQlibVersion().
> Patch 0003 allows libpq.so to be executed directly from the command line to
> print its version, configure arguments etc exactly as PQlibInfoPrint()
> would output them. This is only enabled on x64 linux for now but can be
> extended to other targets quite simply.
+1 --- to me this is the bit that would be most useful, I expect.
It's also kinda cool.
But it's using a bit of a platform quirk that's not supported by the toolchain as well as I'd really like - annoyingly, when you pass a --entrypoint to GNU ld or to LLVM's ld.lld, it should really emit the default .interp section to point to /bin/ld.so.2 or /lib64/ld-linux-x86-64.so.2 as appropriate. But when building -shared they don't seem to want to, nor do they expose a sensible macro that lets you get the default string yourself.
So I thought there was a moderate to high chance that this patch would trip someone's "yuck" meter.
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