Mac OS: C++ printer segfaults

[andreasabel]

Running bnfc-system-tests, I observed that the C++ AST printer for examples/GF/gf.cf https://github.com/BNFC/bnfc/blob/master/examples/GF/gf.cf segfaults when run on examples/GF/example.gf https://github.com/BNFC/bnfc/blob/master/examples/GF/example.gf .

I do not want to debug this. A brief look into the generated printer shows that it has inline functions and destructive update of a buf_ variable.

bnfc/source/src/BNFC/Backend/CPP/PrettyPrinter.hs

Lines 146 to 163 in 344ccde

	" void inline resizeBuffer(void)",
	" {",
	" char *temp = (char *) malloc(buf_size);",
	" if (!temp)",
	" {",
	" fprintf(stderr, \"Error: Out of memory while attempting to grow buffer!\\n\");",
	" exit(1);",
	" }",
	" if (buf_)",
	" {",
	" strcpy(temp, buf_);",
	" free(buf_);",
	" }",
	" buf_ = temp;",
	" }",
	" char *buf_;",
	" int cur_, buf_size;",
	"};",

I leave this to C++ enthusiasts and fans of pointer manipulations. Happy segfaulting!

$ g++ --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.11.45.5)
Target: x86_64-apple-darwin18.0.0
Thread model: posix

[andreasabel]

Ah, I am too good natured, I fixed it anyway.
When you try to strcpy a previously grown buffer buf_ into a buffer temp of BUFFER_INITIAL size, yes, then you segfault on a good operating system.

bnfc/source/src/BNFC/Backend/CPP/PrettyPrinter.hs

Lines 141 to 156 in 344ccde

	" buf_size = " ++ nsDefine inPackage "BUFFER_INITIAL" ++ ";",
	" resizeBuffer();",
	" memset(buf_, 0, buf_size);",
	" }",
	"",
	" void inline resizeBuffer(void)",
	" {",
	" char *temp = (char *) malloc(buf_size);",
	" if (!temp)",
	" {",
	" fprintf(stderr, \"Error: Out of memory while attempting to grow buffer!\\n\");",
	" exit(1);",
	" }",
	" if (buf_)",
	" {",
	" strcpy(temp, buf_);",

Good old buffer overrun. Wonder if someone managed to hack machines with bnfc installed through this.