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README.COMPILER-RT.md

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COMPILER-RT

WHAT IS COMPILER-RT?

Please see http://compiler-rt.llvm.org.

INSTALLATION:

Ensure you have finished build.sh,

then run: ./build_compiler_rt.sh.

By default, installation steps for compiler-rt will be printed to the terminal to run manually, but you can automate the installation process by defining ENABLE_COMPILER_RT_INSTALL.

You can verify compiler-rt is working by invoking the following command:

echo "int main(void){return 0;}" | xcrun clang -xc -o/dev/null -v - 2>&1 | \
  grep "libclang_rt" 1>/dev/null && echo "Success"

If you see "Success", then everything went well.

USAGE:

You do not need to do anything, clang's doing the job for you.

However, -fsanitize=address is a bit annoying because the address sanitizer library is linked
dynamically, and thus requires you to copy the ASAN runtime library onto the target system.

[See README.DEBUGGING in how to get a backtrace with line numbers and symbol names]

The following example illustrates how to achieve this:

# Example source code.
$ cat test.c
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int main(void) {
  char buf[2];
  strcpy(buf, "Hello World"); /* Buffer overflow. */
  puts(buf);
  return 0;
}

# Compile the source file.
$ o64-clang test.c -fsanitize=address -o test

# Ensure the ASAN library is linked in.
$ xcrun otool -L test
test:
        /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 104.1.0) # ASAN dep.
        @rpath/libclang_rt.asan_osx_dynamic.dylib (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1213.0.0)

# Copy 'test' and 'libclang_rt.asan_osx_dynamic.dylib' onto the target system.

# You can find the ASAN library path easily with this one-liner:
$ echo "int main(void){return 0;}" | xcrun clang -fsanitize=address -xc -o/dev/null -v - 2>&1 | \
  tr ' ' '\n' | grep libclang_rt.asan_osx_dynamic.dylib
[...]/bin/../lib/clang/3.6.2/lib/darwin/libclang_rt.asan_osx_dynamic.dylib

# Run ./test on the target system:
$ DYLD_LIBRARY_PATH=. ./test
=================================================================
==410==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff58c3ec72 at pc [...]
WRITE of size 12 at 0x7fff58c3ec72 thread T0
    #0 0x1070029ac  ([...]/tmp/libclang_rt.asan_osx_dynamic.dylib+0x3a9ac)
    #1 0x106fc1d3a  ([...]/tmp/./test+0x100000d3a)
    #2 0x106fc1bd3  ([...]/tmp/./test+0x100000bd3)
    #3 0x0  (<unknown module>)

Address 0x7fff58c3ec72 is located in stack of thread T0 at offset 50 in frame
    #0 0x106fc1bef  ([...]/tmp/./test+0x100000bef)

  This frame has 2 object(s):
    [32, 36) ''
    [48, 50) 'buf' <== Memory access at offset 50 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
Shadow bytes around the buggy address:
  0x1fffeb187d30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187d40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187d50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187d60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187d70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x1fffeb187d80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f2[02]f3
  0x1fffeb187d90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187da0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187db0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187dc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb187dd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==410==ABORTING