RE: [bug fix] Produce a crash dump before main() on Windows

From: Michael Paquier [mailto:michael(at)paquier(dot)xyz]
> No, I really mean a library dependency failure. For example, imagine that
> Postgres is compiled on Windows dynamically, and that it depends on
> libxml2.dll, which is itself compiled dynamically. Then imagine, in a
> custom build echosystem, that a folk comes in and adds lz support to
> libxml2 on Windows. If Postgres still consumes libxml2 but does not add
> in its PATH a version of lz, then a backend in need of libxml2 would fail
> to load, causing Postgres to not start properly. True, painful, story.

I see, that's surely painful. But the DLL in use cannot be overwritten on Windows. So, I assume the following:

1. postmaster loads libxml2.dll without LZ in folder A.
2. Someone adds libxml2.dll with LZ in folder B. folder B is ahead of folder A in postgres's PATH.
3. Some user tries to connect to a database, creating a new child postgres process, which fails to load libxml2.dll in folder B.

> What is ticking me is if the popup window stuff discussed on this thread
> could be a problem in the detection of such dependency errors, as with the
> product I am thinking about, Postgres is not running as a service, but kicked
> by another thing which is a service, and monitors the postmaster.

I understood you are talking about a case where some (server) application uses PostgreSQL internally. That application runs as a Windows service, but PostgreSQL itself doesn't on its own. The application starts PostgreSQL by running pg_ctl start.

In that case, postgres runs under service. I confirmed it with the following test program. This code is extracted from pgwin32_is_service() in PostgreSQL.

--------------------------------------------------
#include <windows.h>
#include <stdio.h>

int
main(void)
{
BOOL IsMember;
PSID ServiceSid;
PSID LocalSystemSid;
SID_IDENTIFIER_AUTHORITY NtAuthority = {SECURITY_NT_AUTHORITY};
FILE *fp;

SetErrorMode(0);

/* Check for service group membership */
if (!AllocateAndInitializeSid(&NtAuthority, 1,
SECURITY_SERVICE_RID, 0, 0, 0, 0, 0, 0, 0,
&ServiceSid))
{
fprintf(stderr, "could not get SID for service group: error code %lu\n",
GetLastError());
return 1;
}

if (!CheckTokenMembership(NULL, ServiceSid, &IsMember))
{
fprintf(stderr, "could not check access token membership: error code %lu\n",
GetLastError());
FreeSid(ServiceSid);
return 1;
}
FreeSid(ServiceSid);

fp = fopen("d:\\a.txt", "a");
if (IsMember)
fprintf(fp, "is under service\n");
else
fprintf(fp, "is not under service\n");

return 0;
}
--------------------------------------------------

You can build the above program with:
cl chksvc.c advapi32.lib

Regards
Takayuki Tsunakawa