Hi! I've noticed that you guys have recently done some changes in GNU Mach's vm_map or thereabouts, and -- I presume -- that is affecting the GDB testsuite in that tests that used to PASS are now no longer considered for execution, because »Memory at address 0 is possibly executable«:
# If we can examine what's at memory address 0, it is possible that we
# could also execute it. This could probably make us run away,
# executing random code, which could have all sorts of ill effects,
# especially on targets without an MMU. Don't run the tests in that
# case.
if { [is_address_zero_readable] } {
untested "Memory at address 0 is possibly executable"
return
}
gdb/testsuite/lib/gdb.exp:is_address_zero_readable:
# Return 1 if the memory at address zero is readable.
gdb_caching_proc is_address_zero_readable {
global gdb_prompt
set ret 0
gdb_test_multiple "x 0" "" {
-re "Cannot access memory at address 0x0.*$gdb_prompt $" {
set ret 0
}
-re ".*$gdb_prompt $" {
set ret 1
}
}
return $ret
}
So, something is really being mapped to and accessible at 0x0:
$ gdb -q /bin/true
Reading symbols from /bin/true...(no debugging symbols found)...done.
(gdb) break exit
Breakpoint 1 at 0x8048cd0
(gdb) r
Starting program: /bin/true
[New Thread 24498.5]
Breakpoint 1, exit (status=0) at exit.c:103
103 exit.c: No such file or directory.
(gdb) x 0
0x0: 0x464c457f
(gdb) print *(int *)0 = 0x1234
$1 = 4660
(gdb) x 0
0x0: 0x00001234
Memory map:
$ vminfo 24498
0[0x1000] (prot=RX, max_prot=RWX, mem_obj=46)
0x1000[0xe000] (prot=RX, max_prot=RWX, mem_obj=46, offs=0x1000)
0xf000[0x1000] (prot=RX, max_prot=RWX, mem_obj=46)
0x10000[0x16000] (prot=RX, max_prot=RWX, mem_obj=46, offs=0x10000)
0x26000[0x1000] (prot=R, max_prot=RWX, mem_obj=46)
0x27000[0x1000] (prot=RW, max_prot=RWX, mem_obj=46)
0x28000[0x1000] (prot=0, max_prot=RWX)
0x29000[0xfff000] (prot=RWX, mem_obj=47)
0x1028000[0x1000] (prot=RWX, mem_obj=47, offs=0xfff000)
0x1029000[0x1000] (prot=RW, max_prot=RWX, mem_obj=48)
0x102a000[0x1000] (prot=RW, max_prot=RWX, mem_obj=49)
0x102c000[0x2000] (prot=RW, max_prot=RWX, mem_obj=49, offs=0x2000)
0x102e000[0x1000] (prot=RW, max_prot=RWX, mem_obj=50)
0x102f000[0xb000] (prot=R, max_prot=RWX, mem_obj=51)
0x103a000[0x61000] (prot=RX, max_prot=RWX, mem_obj=52)
0x109b000[0x1000] (prot=RX, max_prot=RWX, mem_obj=52)
0x109c000[0x155000] (prot=RX, max_prot=RWX, mem_obj=52, offs=0x62000)
0x11f1000[0x3000] (prot=R, max_prot=RWX, mem_obj=52)
0x11f4000[0x2000] (prot=RW, max_prot=RWX, mem_obj=52, offs=0x3000)
0x11f6000[0x4000] (prot=RW, max_prot=RWX, mem_obj=53)
0x11fa000[0x15000] (prot=RX, max_prot=RWX, mem_obj=54)
0x120f000[0x1000] (prot=R, max_prot=RWX, mem_obj=54)
0x1210000[0x1000] (prot=RW, max_prot=RWX, mem_obj=54, offs=0x1000)
0x1211000[0x1000] (prot=RW, max_prot=RWX, mem_obj=55)
0x1212000[0x30000] (prot=RX, max_prot=RWX, mem_obj=56)
0x1242000[0x1000] (prot=R, max_prot=RWX, mem_obj=56)
0x1243000[0x1000] (prot=RW, max_prot=RWX, mem_obj=56, offs=0x1000)
0x1244000[0x2000] (prot=RW, max_prot=RWX, mem_obj=57)
0x1246000[0x1000] (prot=0, max_prot=RWX, mem_obj=57, offs=0x2000)
0x1247000[0x8000] (prot=RW, max_prot=RWX, mem_obj=57, offs=0x3000)
0x124f000[0x1000] (prot=RW, max_prot=RWX, mem_obj=58)
0x8048000[0x1000] (prot=RX, max_prot=RWX, mem_obj=59)
0x8049000[0x5000] (prot=RX, max_prot=RWX, mem_obj=59, offs=0x1000)
0x804e000[0x1000] (prot=R, max_prot=RWX, mem_obj=59)
0x804f000[0x1000] (prot=RW, max_prot=RWX, mem_obj=59)
0x8050000[0x21000] (prot=RWX)
0x8071000[0x7fdf000] (prot=0, max_prot=RWX, offs=0x21000)
Actually...:
(gdb) info sharedlibrary
From To Syms Read Shared Object Library
0x00000db0 0x0001d959 Yes /lib/ld.so
0x01057890 0x0119d9e4 Yes /lib/i386-gnu/libc.so.0.3
0x011fd7d0 0x0120b21f Yes /lib/i386-gnu/libmachuser.so.1
0x012198f0 0x01239bcb Yes /lib/i386-gnu/libhurduser.so.0.3
$ ldd /bin/true
libc.so.0.3 => /lib/i386-gnu/libc.so.0.3 (0x0103a000)
/lib/ld.so => /lib/ld.so.1 (0x00000000)
libmachuser.so.1 => /lib/i386-gnu/libmachuser.so.1 (0x011fa000)
libhurduser.so.0.3 => /lib/i386-gnu/libhurduser.so.0.3 (0x01212000)
The dynamic linker loading straight to 0x0 is most likely not what you
intended? ;-)
Grüße,
Thomas
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