1# 2# Copyright (c) 2025 Mark Johnston <markj@FreeBSD.org> 3# 4# SPDX-License-Identifier: BSD-2-Clause 5# 6 7import gdb 8from freebsd import * 9 10 11class vnet(gdb.Function): 12 """ 13 A function to look up VNET variables by name. 14 15 To look at the value of a VNET variable V_foo, print $V("foo"). The 16 currently selected thread's VNET is used by default, but can be optionally 17 specified as a second parameter, e.g., $V("foo", <vnet>), where <vnet> is a 18 pointer to a struct vnet (e.g., vnet0 or allprison.tqh_first->pr_vnet) or a 19 string naming a jail. 20 """ 21 22 def __init__(self): 23 super(vnet, self).__init__("V") 24 25 def invoke(self, sym, vnet=None): 26 sym = sym.string() 27 if sym.startswith("V_"): 28 sym = sym[len("V_"):] 29 if gdb.lookup_symbol("sysctl___kern_features_vimage")[0] is None: 30 return symval(sym) 31 32 # Look up the VNET's base address. 33 if vnet is None: 34 vnet = tdfind(gdb.selected_thread().ptid[2])['td_vnet'] 35 if not vnet: 36 # If curthread->td_vnet == NULL, vnet0 is the current vnet. 37 vnet = symval("vnet0") 38 elif vnet.type.is_string_like: 39 vnet = vnet.string() 40 for prison in tailq_foreach(symval("allprison"), "pr_list"): 41 if prison['pr_name'].string() == vnet: 42 vnet = prison['pr_vnet'] 43 break 44 else: 45 raise gdb.error(f"No prison named {vnet}") 46 47 def uintptr_t(val): 48 return val.cast(gdb.lookup_type("uintptr_t")) 49 50 # Now the tricky part: compute the address of the symbol relative 51 # to the selected VNET. In the compiled kernel this is done at 52 # load time by applying a magic transformation to relocations 53 # against symbols in the vnet linker set. Here we have to apply 54 # the transformation manually. 55 vnet_data_base = vnet['vnet_data_base'] 56 vnet_entry = symval("vnet_entry_" + sym) 57 vnet_entry_addr = uintptr_t(vnet_entry.address) 58 59 # First, which kernel module does the symbol belong to? 60 for lf in linker_file_foreach(): 61 # Find the bounds of this linker file's VNET linker set. The 62 # struct containing the bounds depends on the type of the linker 63 # file, and unfortunately both are called elf_file_t. So we use a 64 # PC value from the compilation unit (either link_elf.c or 65 # link_elf_obj.c) to disambiguate. 66 block = gdb.block_for_pc(lf['ops']['cls']['methods'][0]['func']) 67 elf_file_t = gdb.lookup_type("elf_file_t", block).target() 68 ef = lf.cast(elf_file_t) 69 70 file_type = lf['ops']['cls']['name'].string() 71 if file_type == "elf64": 72 start = uintptr_t(ef['vnet_start']) 73 if start == 0: 74 # This linker file doesn't have a VNET linker set. 75 continue 76 end = uintptr_t(ef['vnet_stop']) 77 base = uintptr_t(ef['vnet_base']) 78 elif file_type == "elf64_obj": 79 for i in range(ef['nprogtab']): 80 pe = ef['progtab'][i] 81 if pe['name'].string() == "set_vnet": 82 start = uintptr_t(pe['origaddr']) 83 end = start + uintptr_t(pe['size']) 84 base = uintptr_t(pe['addr']) 85 break 86 else: 87 # This linker file doesn't have a VNET linker set. 88 continue 89 else: 90 path = lf['pathname'].string() 91 raise gdb.error(f"{path} has unexpected linker file type {file_type}") 92 93 if vnet_entry_addr >= start and vnet_entry_addr < end: 94 # The symbol belongs to this linker file, so compute the final 95 # address. 96 obj = gdb.Value(vnet_data_base + vnet_entry_addr - start + base) 97 return obj.cast(vnet_entry.type.pointer()).dereference() 98 99 100# Register with gdb. 101vnet() 102