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Also mention that compiler-rt can be needed to build code using `__builtin_available()`. Fixes #278.
4.6 KiB
4.6 KiB
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](README.DEBUGGING.md) 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