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diff --git a/docs/INSTALL.md b/docs/INSTALL.md index e3c06c9d..80d452f7 100644 --- a/docs/INSTALL.md +++ b/docs/INSTALL.md @@ -103,6 +103,41 @@ The llvm instrumentation requires a fully-operational installation of clang. The comes with Xcode is missing some of the essential headers and helper tools. See README.llvm.md for advice on how to build the compiler from scratch. +MacOS X supports SYSV shared memory used by AFL's instrumentation, but the +default settings aren't usable with AFL++. The default settings on 10.14 seem +to be: + +```bash +$ ipcs -M +IPC status from <running system> as of XXX +shminfo: + shmmax: 4194304 (max shared memory segment size) + shmmin: 1 (min shared memory segment size) + shmmni: 32 (max number of shared memory identifiers) + shmseg: 8 (max shared memory segments per process) + shmall: 1024 (max amount of shared memory in pages) +``` + +To temporarily change your settings to something minimally usable with AFL++, +run these commands as root: + +```bash +sysctl kern.sysv.shmmax=8388608 +sysctl kern.sysv.shmall=4096 +``` + +If you're running more than one instance of AFL you likely want to make `shmall` +bigger and increase `shmseg` as well: + +```bash +sysctl kern.sysv.shmmax=8388608 +sysctl kern.sysv.shmseg=48 +sysctl kern.sysv.shmall=98304 +``` + +See http://www.spy-hill.com/help/apple/SharedMemory.html for documentation for +these settings and how to make them permanent. + ## 4. Linux or *BSD on non-x86 systems Standard build will fail on non-x86 systems, but you should be able to |