Re: Can we avoid chdir'ing in resolve_symlinks() ?

Here's a draft patch for this. It seems to work on Linux,
but the Windows code is just speculation. In particular,
I did

path = _fullpath(NULL, fname, 0);
if (path == NULL)
_dosmaperr(GetLastError());

but I'm not really sure that the _dosmaperr bit is needed,
because the _fullpath man page I found makes reference to
setting "errno" [1]. It's likely to be hard to test, because
most of the possible error cases should be nigh unreachable
in our usage; we already know the input is a valid reference
to an executable file.

BTW, I noticed what seems a flat-out bug in validate_exec:

/* Win32 requires a .exe suffix for stat() */
- if (strlen(path) >= strlen(".exe") &&
+ if (strlen(path) < strlen(".exe") ||
pg_strcasecmp(path + strlen(path) - strlen(".exe"), ".exe") != 0)

Nobody's noticed because none of our executables have base names
shorter than 4 characters, but it's still a bug.

regards, tom lane

[1] https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/fullpath-wfullpath?view=msvc-170