MOJOELF_LoaderCallback

A callback used when MojoELF needs to load a new dependency.

Header File

Syntax

typedef void *(*MOJOELF_LoaderCallback)(const char *soname, const char *rpath, const char *runpath);

Function Parameters

soname	the SONAME of the ELF library to load.
rpath	the RPATH entry of the ELF library that needs this dependency. Will be NULL if the library had no such entry.
runpath	the RUNPATH entry of the ELF library that needs this dependency. Will be NULL if the library had no such entry.

Return Value

Returns non-NULL on success, NULL on failure. The returned non-NULL pointer must live until the paired MOJOELF_UnloaderCallback.

Remarks

The "loader" callback doesn't necessarily load anything. All it does it tell MojoELF that it's claiming a specific dependency. For example, if you want to load an ELF that depends on libFoo.so.3, but you plan to override this library without it actually existing, you can write a callback like this...

void *my_loader(const char *soname, const char *rpath, const char *runpath)
{
    return (void *) (strcmp(soname, "libFoo.so.3") == 0);
}

...and MojoELF will not try to load libFoo itself, and assumes you will provide any needed symbols from it via your MOJOELF_ResolverCallback.

Note that your loader can be significantly more complex...it could actually load something, for example, but for some projects, this is all that's needed. What it chooses to load (even if it violates the norms of an ELF loader) is entirely up to its discretion.

The loader callback is provided with any RPATH or RUNPATH entries in the currently-loading ELF, in case finding the correct shared library might need these. Please refer to Linux's dlopen() manpage for details on these strings.

The value returned from the loader callback is opaque data. It will be passed to your MOJOELF_ResolverCallback, and is expected to be free'd in the MOJOELF_UnloaderCallback, if you like.

If this callback returns NULL, the library that MojoELF was in the process of loading will fail to load in response.

Thread Safety

This will be called from the same thread that called into MOJOELF_dlopen_*. Locking is not provided by MojoELF.

Version

This function is available since MojoELF 1.0.0.