Andreas Schwab dixit:
Thorsten Glaser <tg@xxxxxxxxx> writes:
GCC happens to generate these if you use the atomic builtins
even in 4.6 already.
I don't.
You don’t say… oh well.
GCC 4.7 uses the cas instruction, against the recommendations
of the Linux kernel developers. What’s to say? Let’s force it
to use the syscall then.
root@aranym:~ # gcc-4.7 -O2 -g3 -Wall -o t47 t.c -m68000
root@aranym:~ # gdb ./t47
[…]
Dump of assembler code for function main:
0x80000354 <+0>: linkw %fp,#0
0x80000358 <+4>: movel %a3,%sp@-
0x8000035a <+6>: movel %a2,%sp@-
0x8000035c <+8>: movel 0x80003388 <ctr>,%d0
0x80000362 <+14>: movel %d0,%sp@-
0x80000364 <+16>: pea 0x80001248
0x8000036a <+22>: lea 0x80000304 <printf@plt>,%a3
0x80000370 <+28>: jsr %a3@
0x80000372 <+30>: clrl %sp@-
0x80000374 <+32>: lea 0x80000318 <fflush@plt>,%a2
0x8000037a <+38>: jsr %a2@
=> 0x8000037c <+40>: pea 0x1
0x80000380 <+44>: pea 0x80003388 <ctr>
0x80000386 <+50>: jsr 0x80000a06 <__sync_add_and_fetch_4>
0x8000038c <+56>: addql #8,%sp
0x8000038e <+58>: movel 0x80003388 <ctr>,%d0
0x80000394 <+64>: movel %d0,%sp@-
0x80000396 <+66>: pea 0x80001253
0x8000039c <+72>: jsr %a3@
0x8000039e <+74>: clrl %sp@-
0x800003a0 <+76>: jsr %a2@
0x800003a2 <+78>: moveq #0,%d0
[…]
(gdb) si
0x80000a06 in __sync_add_and_fetch_4 ()
(gdb) disas
Dump of assembler code for function __sync_add_and_fetch_4:
=> 0x80000a06 <+0>: linkw %fp,#0
0x80000a0a <+4>: moveml %d2-%d3/%a2,%sp@-
0x80000a0e <+8>: moveal %fp@(8),%a2
0x80000a12 <+12>: movel %a2@,%d2
0x80000a14 <+14>: movel %fp@(12),%d3
0x80000a18 <+18>: addl %d2,%d3
0x80000a1a <+20>: moveal %a2,%a0
0x80000a1c <+22>: movel %d3,%d1
0x80000a1e <+24>: movel #335,%d0
0x80000a24 <+30>: trap #0
0x80000a26 <+32>: cmpl %d2,%d0
0x80000a28 <+34>: bnes 0x80000a34 <__sync_add_and_fetch_4+46>
0x80000a2a <+36>: movel %d3,%d0
0x80000a2c <+38>: moveml %sp@+,%d2-%d3/%a2
0x80000a30 <+42>: unlk %fp
0x80000a32 <+44>: rts
0x80000a34 <+46>: movel %d0,%d2
0x80000a36 <+48>: bras 0x80000a14 <__sync_add_and_fetch_4+14>
End of assembler dump.
[…]
0x80000a24 in __sync_add_and_fetch_4 ()
(gdb) info r
d0 0x14f 335
d1 0x12345679 305419897
d2 0x12345678 305419896
d3 0x12345679 305419897
d4 0x1d 29
d5 0xd004eefc -804983044
d6 0xd004edfc -804983300
d7 0xc 12
a0 0x80003388 0x80003388
a1 0xc014b7f4 0xc014b7f4
a2 0x80003388 0x80003388
a3 0x80000304 0x80000304
a4 0x800003b0 0x800003b0
a5 0xc0148000 0xc0148000
fp 0xef8d4b60 0xef8d4b60
sp 0xef8d4b54 0xef8d4b54
ps 0x8300 [ I0 I1 T1 ]
pc 0x80000a24 0x80000a24 <__sync_add_and_fetch_4+30>
fpcontrol 0x0 0
fpstatus 0x0 0
fpiaddr 0x0 0
(gdb) si
[… aaaaaaand, freeze! ]
Okay. So there’s something wrong with either the way how
GCC uses the syscall, or how the syscall is implemented
in Linux, or how ARAnyM runs that (unlikely).
Additionally, GCC doesn’t use the syscall with -m68020,
which is default in Debian/m68k. Linux and Debian devs,
please comment on whether that should be kept or changed.
Thanks,
//mirabilos
--
“It is inappropriate to require that a time represented as
seconds since the Epoch precisely represent the number of
seconds between the referenced time and the Epoch.”
-- IEEE Std 1003.1b-1993 (POSIX) Section B.2.2.2
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