5 ms·

As far as I know LD_PRELOAD does not allows overriding syscalls, for example mmap. I believe also open call can not be overriden to (because it is a syscall too

As far as I know LD_PRELOAD does not allows overriding syscalls, for example mmap. I believe also open call can not be overriden to (because it is a syscall too), so I wonder how ld-preload-open works? https://stackoverflow.com/a/31439038 https://stackoverflow.com/a/31439038

woodruffw 7y ago
> As far as I know LD_PRELOAD does not allows overriding syscalls, for example mmap. I believe also open call can not be overriden to (because it is a syscall too), so I wonder how ld-preload-open works? LD_PRELOAD does not override syscalls themselves. It can be used to override the wrapper of a syscall. Depending on your libc implementation, kernel version, and architecture, your `mmap` might not be implemented in terms of the `mmap` syscalls. It might be `mmap64` or `mmap2`. Similarly for `open` -- it's currently implemented with `openat` in glibc.
- sigjuice 7y ago
  I don't see mmap(3) or open(3) on FreeBSD, macOS and Linux. Section 2 man pages describe the libc wrappers themselves. See intro(2).
  - woodruffw 7y ago
    Yeah, it looks like I've misremembered. I'll remove the misleading manual sections.