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expr.cc
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expr.cc
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/* expr.cc -- arithmetic expression evaluation. */
/* Copyright (C) 1990-2021 Free Software Foundation, Inc.
This file is part of GNU Bash, the Bourne Again SHell.
Bash is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Bash is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Bash. If not, see <http://www.gnu.org/licenses/>.
*/
/*
All arithmetic is done as int64_t integers with no checking for overflow
(though division by 0 is caught and flagged as an error).
The following operators are handled, grouped into a set of levels in
order of decreasing precedence.
"id++", "id--" [post-increment and post-decrement]
"-", "+" [(unary operators)]
"++id", "--id" [pre-increment and pre-decrement]
"!", "~"
"**" [(exponentiation)]
"*", "/", "%"
"+", "-"
"<<", ">>"
"<=", ">=", "<", ">"
"==", "!="
"&"
"^"
"|"
"&&"
"||"
"expr ? expr : expr"
"=", "*=", "/=", "%=", "+=", "-=", "<<=", ">>=", "&=", "^=", "|="
, [comma]
(Note that most of these operators have special meaning to bash, and an
entire expression should be quoted, e.g. "a=$a+1" or "a=a+1" to ensure
that it is passed intact to the evaluator when using `let'. When using
the $[] or $(( )) forms, the text between the `[' and `]' or `((' and `))'
is treated as if in double quotes.)
Sub-expressions within parentheses have a precedence level greater than
all of the above levels and are evaluated first. Within a single prece-
dence group, evaluation is left-to-right, except for the arithmetic
assignment operator (`='), which is evaluated right-to-left (as in C).
The expression evaluator returns the value of the expression (assignment
statements have as a value what is returned by the RHS). The `let'
builtin, on the other hand, returns 0 if the last expression evaluates to
a non-zero, and 1 otherwise.
Implementation is a recursive-descent parser.
Chet Ramey
chet@po.cwru.edu
*/
#include "config.h"
#include "shell.hh"
namespace bash
{
/* Because of the $((...)) construct, expressions may include newlines.
Here is a macro which accepts newlines, tabs and spaces as whitespace. */
#define cr_whitespace(c) (whitespace (c) || ((c) == '\n'))
/* Maximum amount of recursion allowed. This prevents a non-integer
variable such as "num=num+2" from infinitely adding to itself when
"let num=num+2" is given. */
#define MAX_EXPR_RECURSION_LEVEL 1024
/* This should be the function corresponding to the operator with the
lowest precedence. */
#define EXP_LOWEST expcomma
// Standard error message to use when encountering an invalid array subscript
extern const char *bash_badsub_errmsg;
static int64_t ipow (int64_t base, int64_t exp);
/* Push and save away the contents of the globals describing the
current expression context. */
void
Shell::pushexp ()
{
if (expr_stack.size () >= MAX_EXPR_RECURSION_LEVEL)
evalerror (_ ("expression recursion level exceeded"));
EXPR_CONTEXT *context = new EXPR_CONTEXT (this_expr);
expr_stack.push_back (context);
}
/* Pop the the contents of the expression context stack into the
globals describing the current expression context. */
void
Shell::popexp ()
{
if (expr_stack.empty ())
{
/* See the comment at the top of evalexp() for an explanation of why
this is done. */
this_expr.expression = nullptr;
this_expr.lasttp = nullptr;
evalerror (_ ("recursion stack underflow"));
}
this_expr = *(expr_stack.back ());
delete expr_stack.back ();
expr_stack.pop_back ();
}
void
Shell::expr_unwind ()
{
while (!expr_stack.empty ())
{
EXPR_CONTEXT *context = expr_stack.back ();
delete context;
}
this_expr.noeval = false; /* XXX */
}
void
Shell::expr_bind_variable (const string &lhs, const string &rhs)
{
SHELL_VAR *v;
assign_flags aflags;
if (lhs.empty ())
return; /* XXX */
#if defined(ARRAY_VARS)
aflags
= (assoc_expand_once && already_expanded) ? ASS_NOEXPAND : ASS_NOFLAGS;
aflags |= ASS_ALLOWALLSUB; // allow assoc[@]=value
#else
aflags = ASS_NOFLAGS;
#endif
v = bind_int_variable (lhs, rhs, aflags);
if (v && (v->readonly () || v->noassign ()))
throw bash_exception (FORCE_EOF); /* variable assignment error */
stupidly_hack_special_variables (lhs);
}
#if defined(ARRAY_VARS)
/* This is similar to the logic in arrayfunc.cc:valid_array_reference when
you pass VA_NOEXPAND. */
size_t
Shell::expr_skipsubscript (const char *vp, char *cp)
{
bool isassoc = false;
SHELL_VAR *entry = nullptr;
if (assoc_expand_once & already_expanded)
{
*cp = '\0';
isassoc = legal_identifier (vp) && (entry = find_variable (vp))
&& entry->assoc ();
*cp = '[';
}
int flags
= (isassoc && assoc_expand_once && already_expanded) ? VA_NOEXPAND : 0;
return skipsubscript (cp, 0, flags);
}
/* Rewrite tok, which is of the form vname[expression], to vname[ind], where
IND is the already-calculated value of expression. */
void
Shell::expr_bind_array_element (const string &tok, arrayind_t ind,
const string &rhs)
{
string istr = fmtumax (static_cast<uint64_t> (ind), 10);
string *vname = array_variable_name (tok, 0, nullptr);
if (vname == nullptr)
return;
string lhs (*vname);
delete vname;
lhs.push_back ('[');
lhs += istr;
lhs.push_back (']');
/*itrace("expr_bind_array_element: %s=%s", lhs, rhs);*/
expr_bind_variable (lhs, rhs);
}
#endif /* ARRAY_VARS */
/* Evaluate EXPR, and return the arithmetic result. If VALIDP is
non-null, a zero is stored into the location to which it points
if the expression is invalid, non-zero otherwise. If a non-zero
value is returned in *VALIDP, the return value of evalexp() may
be used.
The `while' loop after the exception is caught relies on the above
implementation of pushexp and popexp leaving in expr_stack[0] the
values that the variables had when the program started. That is,
the first things saved are the initial values of the variables that
were assigned at program startup or by the compiler. Therefore, it is
safe to let the loop terminate when expr_depth == 0, without freeing up
any of the expr_depth[0] stuff. */
int64_t
Shell::evalexp (const string &expr, eval_flags flags, bool *validp)
{
try
{
this_expr.noeval = 0;
already_expanded = (flags & EXP_EXPANDED);
int64_t val = subexpr (expr);
if (validp)
*validp = true;
return val;
}
catch (const eval_exception &)
{
delete[] this_expr.tokstr;
delete[] this_expr.expression;
this_expr.tokstr = nullptr;
this_expr.expression = nullptr;
expr_unwind ();
if (validp)
*validp = false;
return 0;
}
}
int64_t
Shell::subexpr (const string &expr)
{
string::const_iterator it;
for (it = expr.begin (); it != expr.end () && cr_whitespace (*it); ++it)
;
if (it == expr.end ())
return 0;
pushexp ();
this_expr.expression = savestring (expr);
this_expr.tp = this_expr.expression;
this_expr.curtok = this_expr.lasttok = NONE;
this_expr.tokstr = nullptr;
this_expr.tokval = 0;
this_expr.lval.init ();
lastlval = this_expr.lval;
readtok ();
int64_t val = EXP_LOWEST ();
/*TAG:bash-5.3 make it clear that these are arithmetic syntax errors */
if (this_expr.curtok != NONE)
evalerror (_ ("syntax error in expression"));
delete[] this_expr.tokstr;
delete[] this_expr.expression;
popexp ();
return val;
}
int64_t
Shell::expcomma ()
{
int64_t value;
value = expassign ();
while (this_expr.curtok == COMMA)
{
readtok ();
value = expassign ();
}
return value;
}
int64_t
Shell::expassign ()
{
int64_t value;
arrayind_t lind;
value = expcond ();
if (this_expr.curtok == EQ || this_expr.curtok == OP_ASSIGN)
{
token_t op = NONE;
int64_t lvalue = 0;
bool special = (this_expr.curtok == OP_ASSIGN);
if (this_expr.lasttok != STR)
evalerror (_ ("attempted assignment to non-variable"));
if (special)
{
op = assigntok; /* a OP= b */
lvalue = value;
}
if (this_expr.tokstr == nullptr)
evalerror (_ ("syntax error in variable assignment"));
string lhs = this_expr.tokstr;
/* save ind in case rhs is string var and evaluation overwrites it */
lind = this_expr.lval.ind;
readtok ();
value = expassign ();
if (special)
{
if ((op == DIV || op == MOD) && value == 0)
{
if (this_expr.noeval == 0)
evalerror (_ ("division by 0"));
else
value = 1;
}
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wswitch-enum"
#endif
switch (op)
{
case MUL:
/* Handle INTMAX_MIN and INTMAX_MAX * -1 specially here? */
lvalue *= value;
break;
case DIV:
case MOD:
if (lvalue == INTMAX_MIN && value == -1)
lvalue = (op == DIV) ? INTMAX_MIN : 0;
else
lvalue = (op == DIV) ? lvalue / value : lvalue % value;
break;
case PLUS:
lvalue += value;
break;
case MINUS:
lvalue -= value;
break;
case LSH:
lvalue <<= value;
break;
case RSH:
lvalue >>= value;
break;
case BAND:
lvalue &= value;
break;
case BOR:
lvalue |= value;
break;
case BXOR:
lvalue ^= value;
break;
default:
evalerror (_ ("bug: bad expassign token"));
/* NOTREACHED */
}
value = lvalue;
}
#if defined(__clang__)
#pragma clang diagnostic pop
#endif
string rhs = itos (value);
if (this_expr.noeval == 0)
{
#if defined(ARRAY_VARS)
if (lind != -1)
expr_bind_array_element (lhs, lind, rhs);
else
#endif
expr_bind_variable (lhs, rhs);
}
if (this_expr.lval.tokstr == this_expr.tokstr)
this_expr.lval.init ();
delete[] this_expr.tokstr;
this_expr.tokstr = nullptr; /* For freeing on errors. */
}
return value;
}
/* Conditional expression (expr?expr:expr) */
int64_t
Shell::expcond ()
{
int64_t cval, val1, val2, rval;
bool set_noeval = false;
rval = cval = explor ();
if (this_expr.curtok == QUES) /* found conditional expr */
{
if (cval == 0)
{
set_noeval = true;
this_expr.noeval++;
}
readtok ();
if (this_expr.curtok == NONE || this_expr.curtok == COL)
evalerror (_ ("expression expected"));
val1 = EXP_LOWEST ();
if (set_noeval)
this_expr.noeval--;
if (this_expr.curtok != COL)
evalerror (_ ("`:' expected for conditional expression"));
set_noeval = false;
if (cval)
{
set_noeval = true;
this_expr.noeval++;
}
readtok ();
if (this_expr.curtok == 0)
evalerror (_ ("expression expected"));
val2 = expcond ();
if (set_noeval)
this_expr.noeval--;
rval = cval ? val1 : val2;
this_expr.lasttok = COND;
}
return rval;
}
/* Logical OR. */
int64_t
Shell::explor ()
{
int64_t val1 = expland ();
while (this_expr.curtok == LOR)
{
bool set_noeval = false;
if (val1 != 0)
{
this_expr.noeval++;
set_noeval = true;
}
readtok ();
int64_t val2 = expland ();
if (set_noeval)
this_expr.noeval--;
val1 = val1 || val2;
this_expr.lasttok = LOR;
}
return val1;
}
/* Logical AND. */
int64_t
Shell::expland ()
{
int64_t val1 = expbor ();
while (this_expr.curtok == LAND)
{
bool set_noeval = false;
if (val1 == 0)
{
set_noeval = true;
this_expr.noeval++;
}
readtok ();
int64_t val2 = expbor ();
if (set_noeval)
this_expr.noeval--;
val1 = val1 && val2;
this_expr.lasttok = LAND;
}
return val1;
}
/* Bitwise OR. */
int64_t
Shell::expbor ()
{
int64_t val1 = expbxor ();
while (this_expr.curtok == BOR)
{
readtok ();
int64_t val2 = expbxor ();
val1 = val1 | val2;
this_expr.lasttok = NUM;
}
return val1;
}
/* Bitwise XOR. */
int64_t
Shell::expbxor ()
{
int64_t val1 = expband ();
while (this_expr.curtok == BXOR)
{
readtok ();
int64_t val2 = expband ();
val1 = val1 ^ val2;
this_expr.lasttok = NUM;
}
return val1;
}
/* Bitwise AND. */
int64_t
Shell::expband ()
{
int64_t val1 = exp5 ();
while (this_expr.curtok == BAND)
{
readtok ();
int64_t val2 = exp5 ();
val1 = val1 & val2;
this_expr.lasttok = NUM;
}
return val1;
}
int64_t
Shell::exp5 ()
{
int64_t val1 = exp4 ();
while ((this_expr.curtok == EQEQ) || (this_expr.curtok == NEQ))
{
token_t op = this_expr.curtok;
readtok ();
int64_t val2 = exp4 ();
if (op == EQEQ)
val1 = (val1 == val2);
else if (op == NEQ)
val1 = (val1 != val2);
this_expr.lasttok = NUM;
}
return val1;
}
int64_t
Shell::exp4 ()
{
int64_t val1 = expshift ();
while ((this_expr.curtok == LEQ) || (this_expr.curtok == GEQ)
|| (this_expr.curtok == LT) || (this_expr.curtok == GT))
{
token_t op = this_expr.curtok;
readtok ();
int64_t val2 = expshift ();
if (op == LEQ)
val1 = val1 <= val2;
else if (op == GEQ)
val1 = val1 >= val2;
else if (op == LT)
val1 = val1 < val2;
else /* (op == GT) */
val1 = val1 > val2;
this_expr.lasttok = NUM;
}
return val1;
}
/* Left and right shifts. */
int64_t
Shell::expshift ()
{
int64_t val1 = exp3 ();
while ((this_expr.curtok == LSH) || (this_expr.curtok == RSH))
{
token_t op = this_expr.curtok;
readtok ();
int64_t val2 = exp3 ();
if (op == LSH)
val1 = val1 << val2;
else
val1 = val1 >> val2;
this_expr.lasttok = NUM;
}
return val1;
}
int64_t
Shell::exp3 ()
{
int64_t val1 = expmuldiv ();
while ((this_expr.curtok == PLUS) || (this_expr.curtok == MINUS))
{
token_t op = this_expr.curtok;
readtok ();
int64_t val2 = expmuldiv ();
if (op == PLUS)
val1 += val2;
else if (op == MINUS)
val1 -= val2;
this_expr.lasttok = NUM;
}
return val1;
}
int64_t
Shell::expmuldiv ()
{
int64_t val1 = exppower ();
while ((this_expr.curtok == MUL) || (this_expr.curtok == DIV)
|| (this_expr.curtok == MOD))
{
token_t op = this_expr.curtok;
char *stp = this_expr.tp;
readtok ();
int64_t val2 = exppower ();
/* Handle division by 0 and twos-complement arithmetic overflow */
if (((op == DIV) || (op == MOD)) && (val2 == 0))
{
if (this_expr.noeval == 0)
{
this_expr.lasttp = stp;
if (stp)
while (*this_expr.lasttp && whitespace (*this_expr.lasttp))
this_expr.lasttp++;
evalerror (_ ("division by 0"));
}
else
val2 = 1;
}
else if (op == MOD && val1 == INTMAX_MIN && val2 == -1)
{
val1 = 0;
continue;
}
else if (op == DIV && val1 == INTMAX_MIN && val2 == -1)
val2 = 1;
if (op == MUL)
val1 *= val2;
else if (op == DIV || op == MOD)
val1 = (op == DIV) ? val1 / val2 : val1 % val2;
this_expr.lasttok = NUM;
}
return val1;
}
static inline int64_t
ipow (int64_t base, int64_t exp)
{
int64_t result = 1;
while (exp)
{
if (exp & 1)
result *= base;
exp >>= 1;
base *= base;
}
return result;
}
int64_t
Shell::exppower ()
{
int64_t val1 = exp1 ();
while (this_expr.curtok == POWER)
{
readtok ();
int64_t val2 = exppower (); /* exponentiation is right-associative */
this_expr.lasttok = NUM;
if (val2 == 0)
return 1;
if (val2 < 0)
evalerror (_ ("exponent less than 0"));
val1 = ipow (val1, val2);
}
return val1;
}
int64_t
Shell::exp1 ()
{
int64_t val;
if (this_expr.curtok == NOT)
{
readtok ();
val = !exp1 ();
this_expr.lasttok = NUM;
}
else if (this_expr.curtok == BNOT)
{
readtok ();
val = ~exp1 ();
this_expr.lasttok = NUM;
}
else if (this_expr.curtok == MINUS)
{
readtok ();
val = -exp1 ();
this_expr.lasttok = NUM;
}
else if (this_expr.curtok == PLUS)
{
readtok ();
val = exp1 ();
this_expr.lasttok = NUM;
}
else
val = exp0 ();
return val;
}
int64_t
Shell::exp0 ()
{
int64_t val = 0, v2;
EXPR_CONTEXT ec;
/* XXX - might need additional logic here to decide whether or not
pre-increment or pre-decrement is legal at this point. */
if (this_expr.curtok == PREINC || this_expr.curtok == PREDEC)
{
token_t stok = this_expr.lasttok = this_expr.curtok;
readtok ();
if (this_expr.curtok != STR)
/* readtok() catches this */
evalerror (
_ ("identifier expected after pre-increment or pre-decrement"));
v2 = this_expr.tokval + ((stok == PREINC) ? 1 : -1);
string vincdec = itos (v2);
if (this_expr.noeval == 0)
{
#if defined(ARRAY_VARS)
if (this_expr.lval.ind != -1)
expr_bind_array_element (this_expr.lval.tokstr, this_expr.lval.ind,
vincdec);
else
#endif
if (this_expr.tokstr)
expr_bind_variable (this_expr.tokstr, vincdec);
}
val = v2;
this_expr.curtok = NUM; /* make sure --x=7 is flagged as an error */
readtok ();
}
else if (this_expr.curtok == LPAR)
{
/* XXX - save curlval here? Or entire expression context? */
readtok ();
val = EXP_LOWEST ();
if (this_expr.curtok != RPAR)
evalerror (_ ("missing `)'"));
/* Skip over closing paren. */
readtok ();
}
else if ((this_expr.curtok == NUM) || (this_expr.curtok == STR))
{
val = this_expr.tokval;
if (this_expr.curtok == STR)
{
ec = this_expr;
this_expr.tokstr = nullptr; /* keep it from being freed */
this_expr.noeval = 1;
readtok ();
token_t stok = this_expr.curtok;
/* post-increment or post-decrement */
if (stok == POSTINC || stok == POSTDEC)
{
/* restore certain portions of EC */
this_expr.tokstr = ec.tokstr;
this_expr.noeval = ec.noeval;
this_expr.lval = ec.lval;
this_expr.lasttok = STR; /* ec.curtok */
v2 = val + ((stok == POSTINC) ? 1 : -1);
string vincdec = itos (v2);
if (this_expr.noeval == 0)
{
#if defined(ARRAY_VARS)
if (this_expr.lval.ind != -1)
expr_bind_array_element (this_expr.lval.tokstr,
this_expr.lval.ind, vincdec);
else
#endif
expr_bind_variable (this_expr.tokstr, vincdec);
}
this_expr.curtok
= NUM; /* make sure x++=7 is flagged as an error */
}
else
{
/* XXX - watch out for pointer aliasing issues here */
if (stok == STR) /* free new tokstr before old one is restored */
delete[] this_expr.tokstr;
this_expr = ec;
}
}
readtok ();
}
else
evalerror (_ ("syntax error: operand expected"));
return val;
}
int64_t
Shell::expr_streval (char *tok, int e, token_lvalue *lvalue)
{
SHELL_VAR *v;
// itrace("expr_streval: %s: noeval = %d expanded=%d", tok.c_str (),
// this_expr.noeval, already_expanded);
/* If we are suppressing evaluation, just short-circuit here instead of
going through the rest of the evaluator. */
if (this_expr.noeval)
return 0;
size_t initial_depth = expr_stack.size ();
#if defined(ARRAY_VARS)
bool tflag = assoc_expand_once && already_expanded; /* for a start */
#endif
/* [[[[[ */
#if defined(ARRAY_VARS)
av_flags aflag = (tflag) ? AV_NOEXPAND : AV_NOFLAGS;
v = (e == ']') ? array_variable_part (tok, tflag, nullptr, nullptr)
: find_variable (tok);
#else
v = find_variable (tok);
#endif
if (v == nullptr && e != ']')
v = find_variable_last_nameref (tok, 0);
if ((v == nullptr || v->invisible ()) && unbound_vars_is_error)
{
const char *value;
#if defined(ARRAY_VARS)
string *str_value = nullptr;
if (e == ']')
{
str_value = array_variable_name (tok, tflag, nullptr);
value = str_value ? str_value->c_str () : tok;
}
else
#endif
value = tok;
set_exit_status (EXECUTION_FAILURE);
err_unboundvar (value);
#if defined(ARRAY_VARS)
if (e == ']')
delete str_value; /* array_variable_name returns new memory */
#endif
if (no_throw_on_fatal_error && interactive_shell)
throw eval_exception ();
if (interactive_shell)
{
expr_unwind ();
top_level_cleanup ();
throw bash_exception (DISCARD);
}
else
throw bash_exception (FORCE_EOF);
}
string *value;
#if defined(ARRAY_VARS)
array_eltstate_t es (-1);
/* If the second argument to get_array_value doesn't include AV_ALLOWALL,
we don't allow references like array[@]. In this case, get_array_value
is just like get_variable_value in that it does not return newly-allocated
memory or quote the results. AFLAG is set above and is either AV_NOEXPAND
or AV_NOFLAGS. */
value = (e == ']') ? get_array_value (tok, aflag, &es)
: get_variable_value (v);
arrayind_t ind = es.ind;
#else
value = get_variable_value (v);
#endif
if (expr_stack.size () < initial_depth)
{
if (no_throw_on_fatal_error && interactive_shell)
throw eval_exception ();
return 0;
}
int64_t tval = (value && !value->empty ()) ? subexpr (*value) : 0;
if (lvalue)
{
lvalue->tokstr = tok; /* XXX */
lvalue->tokval = tval;
lvalue->tokvar = v; /* XXX */
#if defined(ARRAY_VARS)
lvalue->ind = ind;
#else
lvalue->ind = -1;
#endif
}
return tval;
}
static inline bool
_is_multiop (char c)
{
switch (c)
{
case EQEQ:
case NEQ:
case LEQ:
case GEQ:
case LAND:
case LOR:
case LSH:
case RSH:
case OP_ASSIGN:
case COND:
case POWER:
case PREINC:
case PREDEC:
case POSTINC:
case POSTDEC:
return true;
default:
return false;
}
}
static inline bool
_is_arithop (char c)
{
switch (c)
{
case EQ: