Daniel Jacobowitz wrote:
On Mon, Jul 16, 2007 at 10:43:41AM -0500, Bill Gatliff wrote:
recv(4, 0x7ffffd60, 1, 0) = ? ERESTARTSYS (To be restarted)
--- SIGIO (I/O possible) @ 0 (0) ---
syscall_4294966784(0xa, 0x7ffffd34, 0x1, 0, 0x1008a3c7, 0x1008b5a3, 0x1008b5a4,
That's -512, a.k.a. the errno value used by syscall restarting. I'd
say your glibc does not obey the restartable syscall convention used
by your kernel, and when it tries to restart the syscall the errno
value is not being replaced by the syscall number. Check the assembly
for recv.
Very good catch! Thanks soooo much. Here's the code, from my libc.a:
00000000 <__libc_recv>:
0: 94 21 ff d0 stwu r1,-48(r1)
4: 90 61 00 14 stw r3,20(r1)
8: 90 81 00 18 stw r4,24(r1)
c: 90 a1 00 1c stw r5,28(r1)
10: 90 c1 00 20 stw r6,32(r1)
14: 81 42 00 0c lwz r10,12(r2)
18: 2c 0a 00 00 cmpwi r10,0
1c: 40 82 00 20 bne- 3c <__libc_recv+0x3c>
20: 38 60 00 0a li r3,10
24: 38 81 00 14 addi r4,r1,20
28: 38 00 00 66 li r0,102
2c: 44 00 00 02 sc
30: 38 21 00 30 addi r1,r1,48
34: 4c a3 00 20 bnslr+
38: 48 00 00 00 b 38 <__libc_recv+0x38>
Again, this is 603e on linux-2.4.16 glibc-2.2.5 gcc-2.95.3. (Odd, I
can't seem to find this function in a statically-linked gdbserver, nor
any reference to it in the gdbserver-6.5 source code).
On the kernel side:
_GLOBAL(DoSyscall)
...
blrl /* Call handler */
.globl ret_from_syscall_1
ret_from_syscall_1:
20: stw r3,RESULT(r1) /* Save result */
li r10,-_LAST_ERRNO
cmpl 0,r3,r10
blt 30f
neg r3,r3
cmpi 0,r3,ERESTARTNOHAND
bne 22f
li r3,EINTR
22: lwz r10,_CCR(r1) /* Set SO bit in CR */
oris r10,r10,0x1000
stw r10,_CCR(r1)
30: stw r3,GPR3(r1) /* Update return value */
b ret_from_except
...
ret_from_except:
...
lwz r3,_CCR(r1)
...
mtcrf 0xFF,r3
...
RFI
Now, I'm a little rusty on PPC asm (I've been doing a lot of ARM
lately), but it looks to me like the kernel is setting bit 0 in CR0
(oris r10, r10, 0x1000) a.k.a LT, but the user side is looking at CR0
(bnslr+) bit 3 a.k.a. SO. Or maybe the other way around, I'm not sure
after reading Sections 1.2 and 2.1 of the Programming Environments manual.
Or am I misinterpreting something? I must be, this is well-trodden code
I'm thinking...
The readchar() in gdbserver's remote-utils.c just calls read() on the
file descriptor for the socket. Still trying to track that code down...
b.g.
--
Bill Gatliff
[EMAIL PROTECTED]
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