Hi
* We learn the group of camkes from the
https://github.com/seL4/camkes-tool/blob/master/docs/index.md
* group can colocate two component instances in a single address space, we
want to use the share var by this way, like directcall transfer string virtual
address, But we feel confused about the global symbols who have the same symbol
name include function and variable in a single address space, Their behavior
seems undefined 。
* Our camkes project test below, clien1 and client2 in the same group:
"
import <std_connector.camkes>;
procedure MyInterface {
void print(in string message);
}
component Client {
control;
uses MyInterface iface;
}
component Server {
provides MyInterface iface;
}
assembly {
composition {
group g {
component Client client_1;
component Client client_2;
}
component Server server;
connection seL4RPCCall conn(from g.client_1.iface, from g.client_2.iface, to
server.iface);
}
configuration {
client_1.iface_attributes = 11;
client_2.iface_attributes = 22;
}
}
* 1. We test function in group (a single address space):
* the client code below:
"
#include <camkes.h>
int run(void)
{
char *name = get_instance_name();
iface_print(name);
return 0;
}
"
* the server code below:
"
#include <camkes.h>
#include <stdio.h>
void iface_print(const char *name) {
printf("[%s] ping, the badge is [%d]\n", name, iface_get_sender_id());
}
"
* From the cameks project, we have two client, they are client_1 and
client_2, they have the same they can all “iface_print” to access server
function，In this scene，we have two quesiton:
* Question 1. After compiled the test project, we found in the symbol table
of g_group_bin, we have two "iface_print" symbol, they have different address
even though they have the same name, it look like the componet can call their
own "iface_print", I think in a single address space, component like thread,
Why two symbols with the same name(iface_print) will not conflict in one
address space
* Question 2: when client access server, we offer the _attributes(badge)
for the interface of client, by test, the two client can call their own
"iface_print", but the server can only recevice one badge 22, below is our test:
"
[client_2] ping, the badge is [22]
[client_1] ping, the badge is [22]
"
* The attribute(badge) of client1 is covered by the attribute(badge) of
client2, The iface_print of two client have only one capability to access IPC
endpoint object
* We can not understand in single address space,the "iface_print" of two
component is behavior as one or two different ?
* 2. We test function in global variable (a single address space):
* We found whether global variables are initialized will have completely
different behavior， out test code below:
* scene1 :Client code below:
"
int temp_value;
int run(void)
{
char *name = get_instance_name();
iface_print(name); printf("at start, in %s, the temp_value address is [%p],
value is [0x%lx]\n", name, &temp_value, temp_value); if (strcmp(name,
"client_1") == 0) {
int count = 1000000000;
while(count--) {
asm volatile("");
}
/* client1 read the temp_value*/
printf("at last, in %s, the temp_value address is [%p], value is [0x%lx]\n",
name, &temp_value, temp_value); } else { /* client2 change the val of
temp_value */
temp_value = 0x12345;
printf("at last, in %s, the temp_value address is [%p], value is [0x%lx]\n",
name, &temp_value, temp_value); }
return 0;
}
"
*
Phenomenon: client1 and client2 are different instances of the same code in
same group，form the above code，the symbol of "temp_value" is bss section, the
temp_value of client1 and the temp_value of client2 have the same virtual
address, and if the client2 change the value, client1 can perceive the change，
test as below：
"
at start, in client_1, the temp_value address is [0x659e70], value is [0x0]
at start, in client_2, the temp_value address is [0x659e70], value is [0x0]
at last, in client_2, the temp_value address is [0x659e70], value is [0x12345]
at last, in client_1, the temp_value address is [0x659e70], value is [0x12345]
"
* scene2 :Client code below:
"
int temp_value = 1;
int run(void)
{
char *name = get_instance_name();
iface_print(name); printf("at start, in %s, the temp_value address is [%p],
value is [0x%lx]\n", name, &temp_value, temp_value); if (strcmp(name,
"client_1") == 0) {
int count = 1000000000;
while(count--) {
asm volatile("");
}
/* client1 read the temp_value*/
printf("at last, in %s, the temp_value address is [%p], value is [0x%lx]\n",
name, &temp_value, temp_value); } else { /* client2 change the val of
temp_value */
temp_value = 0x12345;
printf("at last, in %s, the temp_value address is [%p], value is [0x%lx]\n",
name, &temp_value, temp_value); }
return 0;
}
"
* Phenomenon: client1 and client2 are different instances of the same code
in same group，form the above code，the symbol of "temp_value" is data section,
the temp_value of client1 and the temp_value of client2 have the different
virtual address, and if the client2 change the value, client1 can not get the
change， test as below：
"
at last, in client_2, the temp_value address is [0x445ba8], value is [0x12345]
at last, in client_1, the temp_value address is [0x444008], value is [0x1]
"
* The code of scene1 and scene2 are almost the same, except whether
temp_value is initialized， the bss section or data section，but the symbol table
completely different, scene1 the symbol table of g_group_bin has only one
"temp_value" symbol, But scene1 the symbol table of g_group_bin has two symbols
named temp_value, we also do not understand why the same name symbols of global
variable should be one or two in a single address of group. It looks like
random.
Thank you
very much
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