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String copies are bounded: memcpy_s on Windows, __memcpy_chk on Linux and Android - #29
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… and Android
lib.ts copied string bytes with memcpy, trusting each count. Every copy now
goes through boundedCopy(dest, destSize, src, count), which ends the process
rather than write past the destination:
- Windows: the CRT's memcpy_s (its invalid parameter handler fails fast,
0xC0000409)
- Linux and Android: glibc's and Bionic's fortified __memcpy_chk ("buffer
overflow detected"), through __builtin___memcpy_chk, which the compiler
turns back into a plain memcpy where it can prove the copy fits
boundedCopy is a C++ wrapper (src/wrappers/memory.cpp, chosen by #ifdef),
not TypeScript in lib.win32.ts / lib.linux.ts. The compiler now emits
memcpy_s / __memcpy_chk for string copies of its own. Under -mm=rc,
lib.win32.ts made such a copy before a TypeScript declaration of memcpy_s
further down was lowered, and the module failed with "redefinition of
symbol named 'memcpy_s'". memory.cpp is added to build_core.bat, build.sh
and build_android.bat.
regex.cpp's two copies out of std::string use memcpy_s on Windows too.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Summary
lib.tscopied string bytes withmemcpy, trusting each count. Every copy (concat,join,repeat,slice,substring,RegExp.replace,replaceAll) now goes throughboundedCopy(dest, destSize, src, count), which ends the process rather than write past the destination:memcpy_s. Its invalid parameter handler fails fast (0xC0000409).__memcpy_chk("buffer overflow detected"), through__builtin___memcpy_chk. The compiler turns it back into a plainmemcpywhere it can prove the copy fits.boundedCopyis a C++ wrapper (src/wrappers/memory.cpp, platform chosen by#ifdef), declared inlib.native.d.ts. It is not TypeScript inlib.win32.ts/lib.linux.ts: with ASDAlexander77/TypeScriptCompiler#525 the compiler emitsmemcpy_s/__memcpy_chkfor copies of its own. Under-mm=rc,lib.win32.tsmade such a copy before a TypeScriptdeclare function memcpy_sfurther down was lowered, and the module failed with "redefinition of symbol named 'memcpy_s'".memory.cppis added tobuild_core.bat,build.shandbuild_android.bat. The two copies inregex.cppusememcpy_son Windows too.Works with the current compiler, but merge after ASDAlexander77/TypeScriptCompiler#525 (or together) so the compiler's own copies are bounded as well.
Test plan
boundedCopywith a count one byte too large exits0xC0000409; a copy that fits succeedsmemory.cppbuilt with g++ links__memcpy_chk; one byte too many aborts with "buffer overflow detected"build.shand Androidbuild_android.bat: only checked by reading them, not run. This repo has no PR CI; they first run in the release workflow.🤖 Generated with Claude Code