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Daniel Jacobowitz wrote:
<blockquote cite="mid20070716155348.GA5281@caradoc.them.org" type="cite">
<pre wrap="">On Mon, Jul 16, 2007 at 10:43:41AM -0500, Bill Gatliff wrote:
</pre>
<blockquote type="cite">
<pre wrap="">recv(4, 0x7ffffd60, 1, 0) = ? ERESTARTSYS (To be restarted)
--- SIGIO (I/O possible) @ 0 (0) ---
syscall_4294966784(0xa, 0x7ffffd34, 0x1, 0, 0x1008a3c7, 0x1008b5a3, 0x1008b5a4,
</pre>
</blockquote>
<pre wrap=""><!---->
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.
</pre>
</blockquote>
<br>
Very good catch! Thanks soooo much. Here's the code, from my libc.a:<br>
<br>
<tt>00000000 <__libc_recv>:<br>
0: 94 21 ff d0 stwu r1,-48(r1)<br>
4: 90 61 00 14 stw r3,20(r1)<br>
8: 90 81 00 18 stw r4,24(r1)<br>
c: 90 a1 00 1c stw r5,28(r1)<br>
10: 90 c1 00 20 stw r6,32(r1)<br>
14: 81 42 00 0c lwz r10,12(r2)<br>
18: 2c 0a 00 00 cmpwi r10,0<br>
1c: 40 82 00 20 bne- 3c <__libc_recv+0x3c><br>
20: 38 60 00 0a li r3,10<br>
24: 38 81 00 14 addi r4,r1,20<br>
28: 38 00 00 66 li r0,102<br>
2c: 44 00 00 02 sc<br>
30: 38 21 00 30 addi r1,r1,48<br>
34: 4c a3 00 20 bnslr+<br>
38: 48 00 00 00 b 38 <__libc_recv+0x38><br>
</tt><br>
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).<br>
<br>
On the kernel side:<br>
<br>
<tt>_GLOBAL(DoSyscall)<br>
...<br>
blrl /* Call handler */<br>
.globl ret_from_syscall_1<br>
ret_from_syscall_1:<br>
20: stw r3,RESULT(r1) /* Save result */<br>
li r10,-_LAST_ERRNO<br>
cmpl 0,r3,r10<br>
blt 30f<br>
neg r3,r3<br>
cmpi 0,r3,ERESTARTNOHAND<br>
bne 22f<br>
li r3,EINTR<br>
22: lwz r10,_CCR(r1) /* Set SO bit in CR */<br>
oris r10,r10,0x1000<br>
stw r10,_CCR(r1)<br>
30: stw r3,GPR3(r1) /* Update return value */<br>
b ret_from_except<br>
...<br>
ret_from_except:<br>
...<br>
lwz r3,_CCR(r1)<br>
...<br>
mtcrf 0xFF,r3<br>
...<br>
RFI<br>
</tt><br>
<br>
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.<br>
<br>
Or am I misinterpreting something? I must be, this is well-trodden
code I'm thinking...<br>
<br>
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...<br>
<br>
<br>
<br>
b.g.<br>
<pre class="moz-signature" cols="80">--
Bill Gatliff
<a class="moz-txt-link-abbreviated" href="mailto:bgat@billgatliff.com">bgat@billgatliff.com</a>
</pre>
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