freebsd-dev/lib/libkvm/kvm_read.3
John Baldwin 7f911abe54 Add support to libkvm for reading vmcores from other architectures.
- Add a kvaddr_type to represent kernel virtual addresses instead of
  unsigned long.
- Add a struct kvm_nlist which is a stripped down version of struct nlist
  that uses kvaddr_t for n_value.
- Add a kvm_native() routine that returns true if an open kvm descriptor
  is for a native kernel and memory image.
- Add a kvm_open2() function similar to kvm_openfiles().  It drops the
  unused 'swapfile' argument and adds a new function pointer argument for
  a symbol resolving function.  Native kernels still use _fdnlist() from
  libc to resolve symbols if a resolver function is not supplied, but cross
  kernels require a resolver.
- Add a kvm_nlist2() function similar to kvm_nlist() except that it uses
  struct kvm_nlist instead of struct nlist.
- Add a kvm_read2() function similar to kvm_read() except that it uses
  kvaddr_t instead of unsigned long for the kernel virtual address.
- Add a new kvm_arch switch of routines needed by a vmcore backend.
  Each backend is responsible for implementing kvm_read2() for a given
  vmcore format.
- Use libelf to read headers from ELF kernels and cores (except for
  powerpc cores).
- Add internal helper routines for the common page offset hash table used
  by the minidump backends.
- Port all of the existing kvm backends to implement a kvm_arch switch and
  to be cross-friendly by using private constants instead of ones that
  vary by platform (e.g. PAGE_SIZE).  Static assertions are present when
  a given backend is compiled natively to ensure the private constants
  match the real ones.
- Enable all of the existing vmcore backends on all platforms.  This means
  that libkvm on any platform should be able to perform KVA translation
  and read data from a vmcore of any platform.

Tested on:	amd64, i386, sparc64 (marius)
Differential Revision:	https://reviews.freebsd.org/D3341
2015-11-27 18:58:26 +00:00

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.\" @(#)kvm_read.3 8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd November 27, 2015
.Dt KVM_READ 3
.Os
.Sh NAME
.Nm kvm_read ,
.Nm kvm_read2 ,
.Nm kvm_write
.Nd read or write kernel virtual memory
.Sh LIBRARY
.Lb libkvm
.Sh SYNOPSIS
.In kvm.h
.Ft ssize_t
.Fn kvm_read "kvm_t *kd" "unsigned long addr" "void *buf" "size_t nbytes"
.Ft ssize_t
.Fn kvm_read2 "kvm_t *kd" "kvaddr_t addr" "void *buf" "size_t nbytes"
.Ft ssize_t
.Fn kvm_write "kvm_t *kd" "unsigned long addr" "const void *buf" "size_t nbytes"
.Sh DESCRIPTION
The
.Fn kvm_read ,
.Fn kvm_read2 ,
and
.Fn kvm_write
functions are used to read and write kernel virtual memory (or a crash
dump file).
See
.Fn kvm_open 3
for information regarding opening kernel virtual memory and crash dumps.
.Pp
The
.Fn kvm_read
and
.Fn kvm_read2
functions transfer
.Fa nbytes
bytes of data from
the kernel space address
.Fa addr
to
.Fa buf .
Conversely,
.Fn kvm_write
transfers data from
.Fa buf
to
.Fa addr .
Unlike their SunOS counterparts, these functions cannot be used to
read or write process address spaces.
.Pp
The
.Fn kvm_read2
function uses a different type
.Pq Vt kvaddr_t
for the
.Fa addr
argument to allow use of addresses larger than
.Dv ULONG_MAX
when examining non-native kernel images.
.Sh RETURN VALUES
Upon success, the number of bytes actually transferred is returned.
Otherwise, -1 is returned.
.Sh SEE ALSO
.Xr kvm 3 ,
.Xr kvm_close 3 ,
.Xr kvm_getargv 3 ,
.Xr kvm_getenvv 3 ,
.Xr kvm_geterr 3 ,
.Xr kvm_getprocs 3 ,
.Xr kvm_nlist 3 ,
.Xr kvm_open 3 ,
.Xr kvm_openfiles 3