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strlen and wcslen are bound as int, but C returns size_t

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#3,535 2 commenti 0 reazioni 0 assegnatari Vedi su GitHub

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Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
52/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
c, java
Ambito
backend

Direzione di ricerca

Start with the declarations and native stubs named in the issue: C.java and c.c for strlen, plus OS.java and os.c for wcslen. Trace the affected call sites in Font.java and Display.java, and compare with TextLayout.java's cast of g_utf16_strlen. Done means the Java return types and regenerated stubs preserve size_t appropriately, and call sites handle the wider result; the issue reports no tests or build run.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Two C entry points return a size_t and are declared int on the Java side. The stub casts the result down, so the C compiler has nothing to warn about, and nothing anywhere compares the Java declaration with the C one.

/* bundles/org.eclipse.swt/Eclipse SWT PI/common/library/c.c:358 */
rc = (jint)strlen((char *)arg0);
/* string.h */  size_t strlen(const char *);

/* bundles/org.eclipse.swt/Eclipse SWT PI/win32/library/os.c:9855 */
rc = (jint)wcslen((const wchar_t *)arg0);
/* wchar.h */  size_t wcslen(const wchar_t *);

The Java declarations:

/* Eclipse SWT PI/common/org/eclipse/swt/internal/C.java:144      */  public static final native int strlen (long s);
/* Eclipse SWT PI/win32/org/eclipse/swt/internal/win32/OS.java:4554 */  public static final native int wcslen (long string);
What it can cause

On LP64 size_t is 64-bit and jint is 32-bit, so the top 32 bits are dropped unconditionally. For a string of 2 GiB or more the returned length is wrong — and wrong in the worst way, because the cast makes it a plausible small number rather than an obvious failure.

Every call site uses the value directly as a length:

/* Eclipse SWT/gtk/org/eclipse/swt/graphics/Font.java:189      */  int length = C.strlen(family);
/* Eclipse SWT/win32/org/eclipse/swt/widgets/Display.java:3424 */  int length = OS.wcslen (sharedData);

I have not observed a failure and nothing was built or run. Whether a string that long reaches these calls is a question about SWT's own use, not about the declarations.

Suggested fix

SWT already models size_t as Java long everywhere else in the same file. C.java declares eighteen memmove overloads and memset, and every one takes a long annotated cast=(size_t):

/* C.java:141 */  public static final native long memset (long buffer, int c, long num);   /* @param num cast=(size_t) */

strlen and wcslen are the only places size_t appears as a return, and the only two that use int. The repair would be to make them look like the rest — declare long and regenerate the stubs.

Call sites assign to int length, so each would need a cast or a wider local. TextLayout already writes one for the same kind of value:

/* Eclipse SWT/gtk/org/eclipse/swt/graphics/TextLayout.java:655 */
lineEnd = (int)OS.g_utf16_strlen(ptr, -1);
Provenance

Reported as part of ongoing research into cross-language boundaries. Every line above was checked against master on 2026-08-23. No runtime observation; nothing was built or run.

wcslen is Win32-only, where size_t is 64-bit under LLP64 as well, so the narrowing holds on both data models.

Lingua principale
Java
Stelle
202
Fork
206
Merge medio
16h 56m
PR unite (30g)
110

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