LibretroAdmin b9be38fd55 strl: copy string literals without scanning them at runtime ...

strlcpy() begins with strlen() of its source. It lives in another
translation unit, so with no LTO that scan happens at runtime even when
the source is a literal whose length the compiler already measured, and
the call itself cannot be folded away either.

strlcpy_lit() passes the length over as sizeof(). When the destination
size is also a constant -- sizeof(buf), the usual case -- nothing is
left but the stores memcpy() compiles to:

  strlcpy      "core_options"  sizeof(buf)   7.01 ns
  strlcpy_lit  "core_options"  sizeof(buf)   0.42 ns
  strlcpy      41-char literal sizeof(buf)   7.74 ns
  strlcpy_lit  41-char literal sizeof(buf)   0.71 ns
  strlcpy      "core_options"  runtime len   7.11 ns
  strlcpy_lit  "core_options"  runtime len   0.70 ns

The destination bound is kept. When the literal does not fit it defers
to strlcpy(), so the copy truncates as before rather than overrunning;
a form that took only the literal would have turned every one of these
sites into an overflow waiting for a small buffer. The literal is
concatenated with "" so a non-literal source is a compile error rather
than a sizeof() that silently measures a pointer.

818 sites across 104 files were converted by parsing arguments rather
than by pattern-matching text: only a three-argument call whose second
argument is a bare string literal is rewritten, so a macro that happens
to expand to a literal is left alone. Line endings are preserved, so
the CRLF files carry only their own changed lines.

test/compat/test_strl.c compares the two against each other over every
destination size from 0 past the literal's length, for literals that
are empty, single-character, path-shaped, adjacently concatenated and
escape-bearing, checking the return, the terminator and the whole
buffer so an overrun past the terminator is caught. ASan+UBSan+LSan and
TSan both 4/4. The full menu_displaylist_build_list walk over every
displaylist type is byte-identical to before the change
(md5 a2a081bcac09cdc8d72d67efd14ac40e).

2026-08-30 02:10:20 +02:00

..

game_ai.c

strl: copy string literals without scanning them at runtime

2026-08-30 02:10:20 +02:00

game_ai.h

Silence warnings

2025-02-09 20:33:04 +01:00