Difference between Unix and Linux for resolving symbols
I came across a difference between Unix and Linux, when it comes to resolving the symbols from the libs.
consider the following code segments...
Code:
$ cat call1.c
#include <stdio.h>
int a1;
extern int a3;
void prnt_a3()
{
printf("\n%d\n",a3);
}
$ cat test.c
#include <stdio.h>
extern int a1;
int main()
{
int a2=20;
printf("\n%d\n",a1);
return 0;
}
Highlights are...
* a1 is defined in call1 and is being referenced in test.c and is being used also
* a3 is referenced to in test.c and is not defined anywhere. It is being used but in a dead function prnt_a3
I am running it as
Code:
cc -g -c test.c call1.c
ar q lib.a call1.o
cc -g -o test test.o lib.a
The executable gets build in HP Unix bit in Linux, it fails saying
Code:
call1.c:6: undefined reference to `a3'
collect2: ld returned 1 exit status
I don't know the concept/rationale behind the same.
HPUx just refers to the data definitions and it doesn't bother about the functions unless there is atleast 1 function being used from that routine (in which case, HP also gives error) ???
If anyone can suggest some reading material for the same, it'll also be great.
Thanks...
Last edited by Scott; 10-17-2012 at 12:42 PM..
Reason: After almost 5 years, you should know to use code tags :)
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:confused: Hi All
Can anyone help me in finding the answer of the question mentioned below.
What is the difference between Unix & linux ?
Thanks in Advance to all
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hi experts please tell me the real difference between unix and linux at kernel structure (1 Reply)
Discussion started by: linurag
1 Replies
LEARN ABOUT LINUX
get_kernel_syms
GET_KERNEL_SYMS(2) Linux Programmer's Manual GET_KERNEL_SYMS(2)NAME
get_kernel_syms - retrieve exported kernel and module symbols
SYNOPSIS
#include <linux/module.h>
int get_kernel_syms(struct kernel_sym *table);
DESCRIPTION
Note: This system call is present only in kernels before Linux 2.6.
If table is NULL, get_kernel_syms() returns the number of symbols available for query. Otherwise, it fills in a table of structures:
struct kernel_sym {
unsigned long value;
char name[60];
};
The symbols are interspersed with magic symbols of the form #module-name with the kernel having an empty name. The value associated with a
symbol of this form is the address at which the module is loaded.
The symbols exported from each module follow their magic module tag and the modules are returned in the reverse of the order in which they
were loaded.
RETURN VALUE
On success, returns the number of symbols copied to table. On error, -1 is returned and errno is set appropriately.
ERRORS
There is only one possible error return:
ENOSYS get_kernel_syms() is not supported in this version of the kernel.
VERSIONS
This system call is present on Linux only up until kernel 2.4; it was removed in Linux 2.6.
CONFORMING TO
get_kernel_syms() is Linux-specific.
BUGS
There is no way to indicate the size of the buffer allocated for table. If symbols have been added to the kernel since the program queried
for the symbol table size, memory will be corrupted.
The length of exported symbol names is limited to 59 characters.
Because of these limitations, this system call is deprecated in favor of query_module(2) (which is itself nowadays deprecated in favor of
other interfaces described on its manual page).
SEE ALSO create_module(2), delete_module(2), init_module(2), query_module(2)Linux 2012-10-18 GET_KERNEL_SYMS(2)
10-17-2012
