The following patches force structures to be packed on the ARM. The structures
ether_addr and ether_header in ethernet.h must be packed in order for tcpdump to
function correctly. Actually tcpdump has its own version of these structures
but the principle is the same. Similarly the structure tftphdr must be packed
or tftp and tftpd will not function correctly.
The map structure in ksc5601 has a comment that states it should be packed in
all architechures. This is definitely not the case on the ARM. The following
submitted to the libc maintainers. Ulrich is considering whether we need ARM
specific headers. One way or another it should be fixed soon in the CVS tree.
1999-04-14 Scott Bambrough <[EMAIL PROTECTED]>
* sysdeps/unix/sysv/linux/arm/net/ethernet.h:
struct ether_addr and struct ether_header must be packed on the ARM.
The default alignment constraints add padding to the end of the
structures.
1999-04-14 Scott Bambrough <[EMAIL PROTECTED]>
* inet/arpa/tftp.h:
struct tftphdr must be packed on the ARM. The default alignment
constraints
add padding to the end of the structure and between members.
1999-04-14 Scott Bambrough <[EMAIL PROTECTED]>
* iconvdata/ksc5601.h:
struct map should be packed on the ARM. The comment says the structure
should
be packed on all architechures. The default alignment constraints add padding
to the end of the structure.
I found a nasty bug in sysdeps/unix/sysv/linux/arm/socket.S. We had a bug with
ping. It was always printing the error `Socket operation on non-socket.`. An
strace showed the recvfrom call was failing on restart after the signal was
handled. Its parameters were garbage. This is because the socket call never
modifies sp; it moves sp into ip and uses ip to push the args, so it never has
to clean up the stack.
This is nice as it saves one instruction, however the syscall is not an atomic
operation. It can be interrupted if a signal occurs. If the signal handler
uses any stack it trashes the socket call args, because according to it the next
available stack slot is pointed at by sp.
Now for the really bad news. mmap() suffers from the same bug. Yuck!
Good news. Both these patches have been applied to the CVS tree.
1999-04-14 Scott Bambrough <[EMAIL PROTECTED]>
* sysdeps/unix/sysv/linux/arm/socket.S:
Socket calls could not be restarted after being interrupted by
a signal. The parameters on the stack were corrupted by the
signal handler.
* sysdeps/unix/sysv/linux/arm/mmap.S:
mmap calls could not be restarted after being interrupted by
a signal. The parameters on the stack were corrupted by the
signal handler.
Scott
Index: ethernet.h
===================================================================
RCS file: /glibc/cvsfiles/libc/sysdeps/unix/sysv/linux/net/ethernet.h,v
retrieving revision 1.1
diff -r1.1 ethernet.h
36c36
< };
---
> } __attribute__((packed));
44c44
< };
---
> } __attribute__((packed));
Index: ksc5601.h
===================================================================
RCS file: /glibc/cvsfiles/libc/iconvdata/ksc5601.h,v
retrieving revision 1.8
diff -r1.8 ksc5601.h
35,36c35,36
< char val[2];
< };
---
> char val[2] __attribute__((packed));
> } __attribute__((packed));
Index: mmap.S
===================================================================
RCS file: /glibc/cvsfiles/libc/sysdeps/unix/sysv/linux/arm/mmap.S,v
retrieving revision 1.2
diff -r1.2 mmap.S
29,31c29,43
< mov ip, sp
< stmdb ip!, {a1-a4}
< mov a1, ip
---
> /* This code previously moved sp into ip and stored the args using
> stmdb ip!, {a1-a4}. It did not modify sp, so the stack never had
> to be restored after the syscall completed. It saved an
> instruction and meant no stack cleanup work was required.
>
> This will not work in the case of a mmap call being interrupted
> by a signal. If the signal handler uses any stack the arguments
> to mmap will be trashed. The results of a restart of mmap are
> then unpredictable. */
>
> /* store args on the stack */
> stmdb sp!, {a1-a4}
>
> /* do the syscall */
> mov a1, sp
32a45,48
>
> /* pop args off the stack. */
> add sp, sp, #16
>
Index: socket.S
===================================================================
RCS file: /glibc/cvsfiles/libc/sysdeps/unix/sysv/linux/arm/socket.S,v
retrieving revision 1.6
diff -r1.6 socket.S
38,43c38,50
< #define PUSHARGS_1 stmfd ip!, {a1}
< #define PUSHARGS_2 stmfd ip!, {a1, a2}
< #define PUSHARGS_3 stmfd ip!, {a1, a2, a3}
< #define PUSHARGS_4 stmfd ip!, {a1, a2, a3, a4}
< #define PUSHARGS_5 stmfd ip!, {a1, a2, a3, a4} /* Caller has already pushed
arg 5 */
< #define PUSHARGS_6 stmfd ip!, {a1, a2, a3, a4}
---
> #define PUSHARGS_1 stmfd sp!, {a1}
> #define PUSHARGS_2 stmfd sp!, {a1, a2}
> #define PUSHARGS_3 stmfd sp!, {a1, a2, a3}
> #define PUSHARGS_4 stmfd sp!, {a1, a2, a3, a4}
> #define PUSHARGS_5 stmfd sp!, {a1, a2, a3, a4} /* Caller has already pushed
>arg 5 */
> #define PUSHARGS_6 stmfd sp!, {a1, a2, a3, a4}
>
> #define POPARGS_1 add sp, sp, #4
> #define POPARGS_2 add sp, sp, #8
> #define POPARGS_3 add sp, sp, #12
> #define POPARGS_4 add sp, sp, #16
> #define POPARGS_5 add sp, sp, #16
> #define POPARGS_6 add sp, sp, #16
50a58,67
> /* This code previously moved sp into ip and stored the args using
> stmdb ip!, {a1-a4}. It did not modify sp, so the stack never had
> to be restored after the syscall completed. It saved an
> instruction and meant no stack cleanup work was required.
>
> This will not work in the case of a socket call being interrupted
> by a signal. If the signal handler uses any stack the arguments
> to socket will be trashed. The results of a restart of any
> socket call are then unpredictable. */
>
52d68
< mov ip, sp
57c73
< mov a2, ip
---
> mov a2, sp
58a75,77
>
> /* Pop args off the stack */
> P(POPARGS_,NARGS)
Index: tftp.h
===================================================================
RCS file: /glibc/cvsfiles/libc/inet/arpa/tftp.h,v
retrieving revision 1.4
diff -r1.4 tftp.h
59,61c59,61
< } th_u;
< char th_data[1]; /* data or error string */
< };
---
> } __attribute__ ((packed)) th_u;
> char th_data[1] __attribute__((packed)); /* data or error string */
> } __attribute__ ((packed));
