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shell/math: decrease stack usage by not allocating copies of variable names

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We risk exhaust stack with alloca() with old code.

function                                             old     new   delta
arith_apply                                          990    1023     +33
evaluate_string                                     1467    1494     +27
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 60/0)               Total: 60 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2023-06-18 00:47:55 +02:00
parent 182e5a4d00
commit c72c5552ed
1 changed files with 53 additions and 34 deletions
Download patch file Download diff file Expand all files Collapse all files

39
shell/math.c
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@ -245,7 +245,7 @@ is_right_associative(operator prec)
typedef struct {
arith_t val;
char *var_name;
const char *var_name;
} var_or_num_t;
#define VALID_NAME(name) (name)
@ -256,15 +256,28 @@ typedef struct remembered_name {
const char *var_name;
} remembered_name;
static ALWAYS_INLINE int isalnum_(int c)
{
return (isalnum(c) || c == '_');
}
static arith_t
evaluate_string(arith_state_t *math_state, const char *expr);
static const char*
arith_lookup_val(arith_state_t *math_state, var_or_num_t *t)
{
if (VALID_NAME(t->var_name)) {
const char *p = math_state->lookupvar(t->var_name);
const char *name = t->var_name;
char c;
const char *p;
char *e = (char*)endofname(name);
c = *e;
*e = '\0';
p = math_state->lookupvar(name);
*e = c;
if (p) {
size_t len = e - name;
remembered_name *cur;
remembered_name remember;
@ -272,14 +285,16 @@ arith_lookup_val(arith_state_t *math_state, var_or_num_t *t)
* testcase: a=b; b=a; echo $((a))
*/
for (cur = math_state->list_of_recursed_names; cur; cur = cur->next) {
if (strcmp(cur->var_name, t->var_name) == 0) {
if (strncmp(cur->var_name, name, len) == 0
&& !isalnum_(cur->var_name[len])
) {
/* yes */
return "expression recursion loop detected";
}
}
/* push current var name */
remember.var_name = t->var_name;
remember.var_name = name;
remember.next = math_state->list_of_recursed_names;
math_state->list_of_recursed_names = &remember;
@ -293,7 +308,6 @@ arith_lookup_val(arith_state_t *math_state, var_or_num_t *t)
}
/* treat undefined var as 0 */
t->val = 0;
}
return NULL;
}
@ -447,7 +461,13 @@ arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_
}
/* Save to shell variable */
sprintf(buf, ARITH_FMT, rez);
{
char *e = (char*)endofname(top_of_stack->var_name);
char c = *e;
*e = '\0';
math_state->setvar(top_of_stack->var_name, buf);
*e = c;
}
/* After saving, make previous value for v++ or v-- */
if (op == TOK_POST_INC)
rez--;
@ -610,6 +630,7 @@ evaluate_string(arith_state_t *math_state, const char *expr)
* (modulo "09v09v09v09v09v" case,
* but we have code to detect that early)
*/
dbg("expr:'%s' expr_len:%u", expr, expr_len);
numstackptr = numstack = alloca((expr_len / 2) * sizeof(numstack[0]));
opstackptr = opstack = alloca(expr_len * sizeof(opstack[0]));
}
@ -655,10 +676,8 @@ evaluate_string(arith_state_t *math_state, const char *expr)
if (p != expr) {
/* Name */
if (!math_state->evaluation_disabled) {
size_t var_name_size = (p - expr) + 1; /* +1 for NUL */
numstackptr->var_name = alloca(var_name_size);
safe_strncpy(numstackptr->var_name, expr, var_name_size);
dbg("[%d] var:'%s'", (int)(numstackptr - numstack), numstackptr->var_name);
numstackptr->var_name = expr;
dbg("[%d] var:'%.*s'", (int)(numstackptr - numstack), (int)(p - expr), expr);
expr = skip_whitespace(p);
/* If it is not followed by "=" operator... */
if (expr[0] != '=' /* not "=..." */