strlen and wcslen are bound as int, but C returns size_t #3535

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.