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A unit reached only TRANSITIVELY crashes the program at startup

Repro — three lines, no network, no SSL

program t;
uses blcksock;
begin WriteLn('ok'); end.



$ pxx --mimic-fpc -Fuexternal/synapse -Fulib/rtl -Fulib/rtl/platform/posix t.pas t
ok: ...
$ ./t
Segmentation fault

ok is never printed — it dies before the main body runs.

The fix that shouldn't be one

Naming a unit that blcksock already uses, BEFORE it, makes the crash go away:

uses clause result
blcksock segfault
blcksock, sysutils segfault
sysutils, blcksock segfault
classes, blcksock segfault
synacode, blcksock segfault
synsock, blcksock segfault
synafpc, blcksock segfault
synaip, blcksock ok
synautil, blcksock ok (synautil is the one that drags in synaip)
httpsend segfault
smtpsend segfault

So it is specifically synaip that has to be linked earlier, and mentioning it in the program's own uses clause is the whole difference. synaip has NO initialization section — a plain end. — so this is not an initialization-ordering semantic; something about the ORDER units are emitted in changes whether the program survives startup.

This also explains why test/lib_synapse.pas is green and has been all along: it happens to write uses synacode, synautil, blcksock, sysutils — synautil is in front, so it takes the working path by accident.

Where it dies

Program received signal SIGSEGV
0x00000000004000bd in ?? ()
=> 0x4000bd:  decq   -0x10(%rax)      <- the managed-string RELEASE helper
   0x4000c1:  jne    0x4000e7

It is inside the refcount-decrement helper with a bad %rax, i.e. something is releasing a managed string through a pointer that was never a string. The apparent return address (0x4946c8) disassembles as data, so the frame is not a real call chain — the helper is being entered with a stack that is not a caller's.

Note the failure is at STARTUP with an empty program body, so the offending release is in unit init/finalization emission, not in user code.

Why it matters beyond Synapse

uses <one unit> is the most ordinary line in Pascal. Whether a program starts currently depends on whether its author happened to name a transitive dependency first — which is not something a user can be expected to discover, and which makes any green test using that library only accidentally green. It blocks the Synapse SSL end-to-end (httpsend + ssl_openssl3 crash the same way), which is the last open item of [[feature-real-dynlib-loader]].

Requires --mimic-fpc only because Synapse needs it to compile at all; the flag is not otherwise implicated.

[[bug-pascal-uses-is-transitive]] is about transitive VISIBILITY of names; this is about a transitively-reached unit being emitted in an order that breaks startup. They may share a cause — worth checking together.

Gate

make test + self-host byte-identical, plus a regression that compiles program t; uses blcksock; begin WriteLn('ok') end. and asserts it prints ok — the three-line form above, with no unit named ahead of it.

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