FreeBSD Manual Pages
KVM(3) Library Functions Manual KVM(3) NAME kvm -- kernel memory interface LIBRARY Kernel Data Access Library (libkvm, -lkvm) DESCRIPTION The kvm library provides a uniform interface for accessing kernel vir- tual memory images, including live systems and crash dumps. Access to live systems is via sysctl(3) for some functions, and mem(4) and kmem(4) for other functions, while crash dumps can be examined via the core file generated by savecore(8). The interface behaves similarly in both cases. Memory can be read and written, kernel symbol addresses can be looked up efficiently, and information about user processes can be gathered. The kvm_open() function is first called to obtain a descriptor for all subsequent calls. COMPATIBILITY The kvm interface was first introduced in SunOS. A considerable number of programs have been developed that use this interface, making back- ward compatibility highly desirable. In most respects, the Sun kvm in- terface is consistent and clean. Accordingly, the generic portion of the interface (i.e., kvm_open(), kvm_close(), kvm_read(), kvm_write(), and kvm_nlist()) has been incorporated into the BSD interface. Indeed, many kvm applications (i.e., debuggers and statistical monitors) use only this subset of the interface. The process interface was not kept. This is not a portability issue since any code that manipulates processes is inherently machine depen- dent. Finally, the Sun kvm error reporting semantics are poorly defined. The library can be configured either to print errors to stderr automati- cally, or to print no error messages at all. In the latter case, the nature of the error cannot be determined. To overcome this, the BSD interface includes a routine, kvm_geterr(3), to return (not print out) the error message corresponding to the most recent error condition on the given descriptor. CROSS DEBUGGING The kvm library supports inspection of crash dumps from non-native ker- nels. Only a limited subset of the kvm interface is supported for these dumps. To inspect a crash dump of a non-native kernel, the caller must provide a resolver function when opening a descriptor via kvm_open2(). In addition, the kvm interface defines an integer type (kvaddr_t) that is large enough to hold all valid addresses of all sup- ported architectures. The interface also defines a new namelist struc- ture type (struct kvm_nlist) for use with kvm_nlist2(). To avoid ad- dress truncation issues, the caller should use kvm_nlist2() and kvm_read2() in place of kvm_nlist() and kvm_read(), respectively. Fi- nally, only a limited subset of operations are supported for non-native crash dumps: kvm_close(), kvm_geterr(), kvm_kerndisp(), kvm_open2(), kvm_native(), kvm_nlist2(), and kvm_read2(). SEE ALSO kvm_close(3), kvm_getargv(3), kvm_getenvv(3), kvm_geterr(3), kvm_getloadavg(3), kvm_getprocs(3), kvm_getswapinfo(3), kvm_kerndisp(3), kvm_native(3), kvm_nlist(3), kvm_nlist2(3), kvm_open(3), kvm_open2(3), kvm_openfiles(3), kvm_read(3), kvm_read2(3), kvm_write(3), sysctl(3), kmem(4), mem(4) HISTORY The kvm_native(), kvm_nlist2(), kvm_open2(), and kvm_read2() functions first appeared in FreeBSD 11.0. FreeBSD 14.3 February 5, 2020 KVM(3)
NAME | LIBRARY | DESCRIPTION | COMPATIBILITY | CROSS DEBUGGING | SEE ALSO | HISTORY
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