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b875d7c136
Also mention that compiler-rt can be needed to build code using `__builtin_available()`. Fixes #278.
118 lines
4.6 KiB
Markdown
118 lines
4.6 KiB
Markdown
## COMPILER-RT ##
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### WHAT IS COMPILER-RT? ###
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Please see http://compiler-rt.llvm.org.
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### INSTALLATION: ###
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Ensure you have finished `build.sh`,
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then run: `./build_compiler_rt.sh`.
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By default, installation steps for compiler-rt will be printed to the terminal
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to run manually, but you can automate the installation process by defining
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`ENABLE_COMPILER_RT_INSTALL`.
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You can verify compiler-rt is working by invoking the following command:
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echo "int main(void){return 0;}" | xcrun clang -xc -o/dev/null -v - 2>&1 | \
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grep "libclang_rt" 1>/dev/null && echo "Success"
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If you see "Success", then everything went well.
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### USAGE: ###
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You do not need to do anything, clang's doing the job for you.
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However, `-fsanitize=address` is a bit annoying because the address sanitizer library is linked
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dynamically, and thus requires you to copy the ASAN runtime library onto the target system.
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\[See [README.DEBUGGING](README.DEBUGGING.md) in how to get a backtrace with line numbers and symbol names]
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The following example illustrates how to achieve this:
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# Example source code.
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$ cat test.c
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#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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int main(void) {
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char buf[2];
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strcpy(buf, "Hello World"); /* Buffer overflow. */
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puts(buf);
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return 0;
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}
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# Compile the source file.
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$ o64-clang test.c -fsanitize=address -o test
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# Ensure the ASAN library is linked in.
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$ xcrun otool -L test
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test:
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/usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 104.1.0) # ASAN dep.
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@rpath/libclang_rt.asan_osx_dynamic.dylib (compatibility version 0.0.0, current version 0.0.0)
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/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1213.0.0)
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# Copy 'test' and 'libclang_rt.asan_osx_dynamic.dylib' onto the target system.
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# You can find the ASAN library path easily with this one-liner:
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$ echo "int main(void){return 0;}" | xcrun clang -fsanitize=address -xc -o/dev/null -v - 2>&1 | \
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tr ' ' '\n' | grep libclang_rt.asan_osx_dynamic.dylib
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[...]/bin/../lib/clang/3.6.2/lib/darwin/libclang_rt.asan_osx_dynamic.dylib
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# Run ./test on the target system:
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$ DYLD_LIBRARY_PATH=. ./test
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=================================================================
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==410==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff58c3ec72 at pc [...]
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WRITE of size 12 at 0x7fff58c3ec72 thread T0
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#0 0x1070029ac ([...]/tmp/libclang_rt.asan_osx_dynamic.dylib+0x3a9ac)
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#1 0x106fc1d3a ([...]/tmp/./test+0x100000d3a)
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#2 0x106fc1bd3 ([...]/tmp/./test+0x100000bd3)
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#3 0x0 (<unknown module>)
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Address 0x7fff58c3ec72 is located in stack of thread T0 at offset 50 in frame
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#0 0x106fc1bef ([...]/tmp/./test+0x100000bef)
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This frame has 2 object(s):
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[32, 36) ''
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[48, 50) 'buf' <== Memory access at offset 50 overflows this variable
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HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
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(longjmp and C++ exceptions *are* supported)
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Shadow bytes around the buggy address:
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0x1fffeb187d30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187d40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187d50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187d60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187d70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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=>0x1fffeb187d80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f2[02]f3
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0x1fffeb187d90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187da0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187db0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187dc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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0x1fffeb187dd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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Shadow byte legend (one shadow byte represents 8 application bytes):
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Addressable: 00
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Partially addressable: 01 02 03 04 05 06 07
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Heap left redzone: fa
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Heap right redzone: fb
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Freed heap region: fd
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Stack left redzone: f1
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Stack mid redzone: f2
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Stack right redzone: f3
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Stack partial redzone: f4
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Stack after return: f5
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Stack use after scope: f8
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Global redzone: f9
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Global init order: f6
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Poisoned by user: f7
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Container overflow: fc
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Array cookie: ac
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Intra object redzone: bb
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ASan internal: fe
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Left alloca redzone: ca
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Right alloca redzone: cb
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==410==ABORTING
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