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bus: implement message_read_ap() non-recursively

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As it turns out if you pass a va_list to a function its state becomes
undefined after that function returns, and this actually does break on
x86-32.

Hence, let's reimplement message_read_ap() without the use of recursion.
Instead we now build our own stack of types in an array so that we can
decode the entire parameter list in a single stackframe.
This commit is contained in:
Lennart Poettering 2013-04-09 21:03:12 +02:00
parent 8df31a9c98
commit fe1d424d29
1 changed files with 114 additions and 34 deletions
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148
src/libsystemd-bus/bus-message.c
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@ -2091,14 +2091,89 @@ int sd_bus_message_rewind(sd_bus_message *m, int complete) {
return !isempty(c->signature);
}
typedef struct {
const char *types;
unsigned n_struct;
unsigned n_array;
} TypeStack;
static int type_stack_push(TypeStack *stack, unsigned max, unsigned *i, const char *types, unsigned n_struct, unsigned n_array) {
assert(stack);
assert(max > 0);
if (*i >= max)
return -EINVAL;
stack[*i].types = types;
stack[*i].n_struct = n_struct;
stack[*i].n_array = n_array;
(*i)++;
return 0;
}
static int type_stack_pop(TypeStack *stack, unsigned max, unsigned *i, const char **types, unsigned *n_struct, unsigned *n_array) {
assert(stack);
assert(max > 0);
assert(types);
assert(n_struct);
assert(n_array);
if (*i <= 0)
return 0;
(*i)--;
*types = stack[*i].types;
*n_struct = stack[*i].n_struct;
*n_array = stack[*i].n_array;
return 1;
}
static int message_read_ap(sd_bus_message *m, const char *types, va_list ap) {
const char *t;
unsigned n_array, n_struct;
TypeStack stack[BUS_CONTAINER_DEPTH];
unsigned stack_ptr = 0;
int r;
assert(m);
assert(types);
for (t = types; *t; t++) {
/* Ideally, we'd just call ourselves recursively on every
* complex type. However, the state of a va_list that is
* passed to a function is undefined after that function
* returns. This means we need to docode the va_list linearly
* in a single stackframe. We hence implement our own
* home-grown stack in an array. */
n_array = (unsigned) -1;
n_struct = strlen(types);
for (;;) {
const char *t;
if (n_array == 0 || (n_struct == 0 && n_array == (unsigned) -1)) {
r = type_stack_pop(stack, ELEMENTSOF(stack), &stack_ptr, &types, &n_struct, &n_array);
if (r < 0)
return r;
if (r == 0)
break;
r = sd_bus_message_exit_container(m);
if (r < 0)
return r;
continue;
}
t = types;
if (n_array != (unsigned) -1)
n_array --;
else {
types ++;
n_struct--;
}
switch (*t) {
case SD_BUS_TYPE_BYTE:
@ -2118,6 +2193,11 @@ static int message_read_ap(sd_bus_message *m, const char *types, va_list ap) {
p = va_arg(ap, void*);
r = sd_bus_message_read_basic(m, *t, p);
if (r < 0)
return r;
if (r == 0)
return -ENXIO;
break;
}
@ -2129,29 +2209,30 @@ static int message_read_ap(sd_bus_message *m, const char *types, va_list ap) {
return r;
{
unsigned i, n;
char s[k + 1];
memcpy(s, t + 1, k);
s[k] = 0;
t += k;
r = sd_bus_message_enter_container(m, SD_BUS_TYPE_ARRAY, s);
if (r < 0)
return r;
if (r == 0)
return -ENXIO;
n = va_arg(ap, unsigned);
for (i = 0; i < n; i++) {
r = message_read_ap(m, s, ap);
if (r < 0)
return r;
}
r = sd_bus_message_exit_container(m);
}
if (n_array == (unsigned) -1) {
types += k;
n_struct -= k;
}
r = type_stack_push(stack, ELEMENTSOF(stack), &stack_ptr, types, n_struct, n_array);
if (r < 0)
return r;
types = t + 1;
n_struct = k;
n_array = va_arg(ap, unsigned);
break;
}
@ -2168,13 +2249,14 @@ static int message_read_ap(sd_bus_message *m, const char *types, va_list ap) {
if (r == 0)
return -ENXIO;
r = message_read_ap(m, s, ap);
r = type_stack_push(stack, ELEMENTSOF(stack), &stack_ptr, types, n_struct, n_array);
if (r < 0)
return r;
if (r == 0)
return -ENXIO;
r = sd_bus_message_exit_container(m);
types = s;
n_struct = strlen(s);
n_array = (unsigned) -1;
break;
}
@ -2196,29 +2278,27 @@ static int message_read_ap(sd_bus_message *m, const char *types, va_list ap) {
return r;
if (r == 0)
return -ENXIO;
t += k - 1;
r = message_read_ap(m, s, ap);
if (r < 0)
return r;
if (r == 0)
return -ENXIO;
r = sd_bus_message_exit_container(m);
}
if (n_array == (unsigned) -1) {
types += k - 1;
n_struct -= k - 1;
}
r = type_stack_push(stack, ELEMENTSOF(stack), &stack_ptr, types, n_struct, n_array);
if (r < 0)
return r;
types = t + 1;
n_struct = k - 2;
n_array = (unsigned) -1;
break;
}
default:
r = -EINVAL;
return -EINVAL;
}
if (r < 0)
return r;
if (r == 0)
return -ENXIO;
}
return 1;