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nasm/asm/quote.c
H. Peter Anvin db6960c3fa quote: improve comment 
Explain why 0xfc + vb5 cannot overflow a byte value.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2019-06-06 17:32:44 -07:00

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/* ----------------------------------------------------------------------- *
*
* Copyright 1996-2019 The NASM Authors - All Rights Reserved
* See the file AUTHORS included with the NASM distribution for
* the specific copyright holders.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following
* conditions are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* ----------------------------------------------------------------------- */
/*
* quote.c
*/
#include "compiler.h"
#include "nasmlib.h"
#include "quote.h"
#include "nctype.h"
#include "error.h"
/*
* Create a NASM quoted string in newly allocated memory. Update the
* *lenp parameter with the output length (sans final NUL).
*/
char *nasm_quote(const char *str, size_t *lenp)
{
const char *p, *ep;
char c, c1, *q, *nstr;
unsigned char uc;
bool sq_ok, dq_ok;
size_t qlen;
size_t len = *lenp;
sq_ok = dq_ok = true;
ep = str+len;
qlen = 0; /* Length if we need `...` quotes */
for (p = str; p < ep; p++) {
c = *p;
switch (c) {
case '\'':
sq_ok = false;
qlen++;
break;
case '\"':
dq_ok = false;
qlen++;
break;
case '`':
case '\\':
qlen += 2;
break;
default:
if (c < ' ' || c > '~') {
sq_ok = dq_ok = false;
switch (c) {
case '\a':
case '\b':
case '\t':
case '\n':
case '\v':
case '\f':
case '\r':
case 27:
qlen += 2;
break;
default:
c1 = (p+1 < ep) ? p[1] : 0;
if (c1 >= '0' && c1 <= '7')
uc = 0377; /* Must use the full form */
else
uc = c;
if (uc > 077)
qlen++;
if (uc > 07)
qlen++;
qlen += 2;
break;
}
} else {
qlen++;
}
break;
}
}
if (sq_ok || dq_ok) {
/* Use '...' or "..." */
nstr = nasm_malloc(len+3);
nstr[0] = nstr[len+1] = sq_ok ? '\'' : '\"';
q = &nstr[len+2];
if (len > 0)
memcpy(nstr+1, str, len);
} else {
/* Need to use `...` quoted syntax */
nstr = nasm_malloc(qlen+3);
q = nstr;
*q++ = '`';
for (p = str; p < ep; p++) {
c = *p;
switch (c) {
case '`':
case '\\':
*q++ = '\\';
*q++ = c;
break;
case 7:
*q++ = '\\';
*q++ = 'a';
break;
case 8:
*q++ = '\\';
*q++ = 'b';
break;
case 9:
*q++ = '\\';
*q++ = 't';
break;
case 10:
*q++ = '\\';
*q++ = 'n';
break;
case 11:
*q++ = '\\';
*q++ = 'v';
break;
case 12:
*q++ = '\\';
*q++ = 'f';
break;
case 13:
*q++ = '\\';
*q++ = 'r';
break;
case 27:
*q++ = '\\';
*q++ = 'e';
break;
default:
if (c < ' ' || c > '~') {
c1 = (p+1 < ep) ? p[1] : 0;
if (c1 >= '0' && c1 <= '7')
uc = 0377; /* Must use the full form */
else
uc = c;
*q++ = '\\';
if (uc > 077)
*q++ = ((unsigned char)c >> 6) + '0';
if (uc > 07)
*q++ = (((unsigned char)c >> 3) & 7) + '0';
*q++ = ((unsigned char)c & 7) + '0';
break;
} else {
*q++ = c;
}
break;
}
}
*q++ = '`';
nasm_assert((size_t)(q-nstr) == qlen+2);
}
*q = '\0';
*lenp = q - nstr;
return nstr;
}
static unsigned char *emit_utf8(unsigned char *q, uint32_t v)
{
uint32_t vb1, vb2, vb3, vb4, vb5;
if (v <= 0x7f) {
*q++ = v;
goto out0;
}
vb1 = v >> 6;
if (vb1 <= 0x1f) {
*q++ = 0xc0 + vb1;
goto out1;
}
vb2 = vb1 >> 6;
if (vb2 <= 0x0f) {
*q++ = 0xe0 + vb2;
goto out2;
}
vb3 = vb2 >> 6;
if (vb3 <= 0x07) {
*q++ = 0xf0 + vb3;
goto out3;
}
vb4 = vb3 >> 6;
if (vb4 <= 0x03) {
*q++ = 0xf8 + vb4;
goto out4;
}
/*
* Note: this is invalid even for "classic" (pre-UTF16) 31-bit
* UTF-8 if the value is >= 0x8000000. This at least tries to do
* something vaguely sensible with it. Caveat programmer.
* The __utf*__ string transform functions do reject these
* as invalid input.
*
* vb5 cannot be more than 3, as a 32-bit value has been shifted
* right by 5*6 = 30 bits already.
*/
vb5 = vb4 >> 6;
*q++ = 0xfc + vb5;
goto out5;
/* Emit extension bytes as appropriate */
out5: *q++ = 0x80 + (vb4 & 63);
out4: *q++ = 0x80 + (vb3 & 63);
out3: *q++ = 0x80 + (vb2 & 63);
out2: *q++ = 0x80 + (vb1 & 63);
out1: *q++ = 0x80 + (v & 63);
out0: return q;
}
static inline uint32_t ctlbit(uint32_t v)
{
return unlikely(v < 32) ? UINT32_C(1) << v : 0;
}
#define CTL_ERR(c) \
(badctl & (ctlmask |= ctlbit(c)))
#define EMIT_UTF8(c) \
do { \
uint32_t ec = (c); \
if (!CTL_ERR(ec)) \
q = emit_utf8(q, ec); \
} while (0)
#define EMIT(c) \
do { \
unsigned char ec = (c); \
if (!CTL_ERR(ec)) \
*q++ = ec; \
} while (0)
/*
* Same as nasm_quote, but take the length of a C string;
* the lenp argument is optional.
*/
char *nasm_quote_cstr(const char *str, size_t *lenp)
{
size_t len = strlen(str);
char *qstr = nasm_quote(str, &len);
if (lenp)
*lenp = len;
return qstr;
}
/*
* Do an *in-place* dequoting of the specified string, returning the
* resulting length (which may be containing embedded nulls.)
*
* In-place replacement is possible since the unquoted length is always
* shorter than or equal to the quoted length.
*
* *ep points to the final quote, or to the null if improperly quoted.
*
* Issue an error if the string contains control characters
* corresponding to bits set in badctl; in that case, the output
* string, but not *ep, is truncated before the first invalid
* character.
*/
static size_t nasm_unquote_common(char *str, char **ep,
const uint32_t badctl)
{
unsigned char bq;
const unsigned char *p;
const unsigned char *escp = NULL;
unsigned char *q;
unsigned char c;
uint32_t ctlmask = 0; /* Mask of control characters seen */
enum unq_state {
st_start,
st_backslash,
st_hex,
st_oct,
st_ucs,
st_done
} state;
int ndig = 0;
uint32_t nval = 0;
p = q = (unsigned char *)str;
bq = *p++;
if (!bq)
return 0;
switch (bq) {
case '\'':
case '\"':
/* '...' or "..." string */
while ((c = *p++) && (c != bq))
EMIT(c);
break;
case '`':
/* `...` string */
state = st_start;
while (state != st_done) {
c = *p++;
switch (state) {
case st_start:
switch (c) {
case '\\':
state = st_backslash;
break;
case '`':
case '\0':
state = st_done;
break;
default:
EMIT(c);
break;
}
break;
case st_backslash:
state = st_start;
escp = p; /* Beginning of argument sequence */
nval = 0;
switch (c) {
case 'a':
nval = 7;
break;
case 'b':
nval = 8;
break;
case 'e':
nval = 27;
break;
case 'f':
nval = 12;
break;
case 'n':
nval = 10;
break;
case 'r':
nval = 13;
break;
case 't':
nval = 9;
break;
case 'u':
state = st_ucs;
ndig = 4;
break;
case 'U':
state = st_ucs;
ndig = 8;
break;
case 'v':
nval = 11;
break;
case 'x':
case 'X':
state = st_hex;
ndig = 2;
break;
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
state = st_oct;
ndig = 2; /* Up to two more digits */
nval = c - '0';
break;
case '\0':
nval = '\\';
p--; /* Reprocess; terminates string */
break;
default:
nval = c;
break;
}
if (state == st_start)
EMIT(nval);
break;
case st_oct:
if (c >= '0' && c <= '7') {
nval = (nval << 3) + (c - '0');
if (--ndig)
break; /* Might have more digits */
} else {
p--; /* Process this character again */
}
EMIT(nval);
state = st_start;
break;
case st_hex:
case st_ucs:
if (nasm_isxdigit(c)) {
nval = (nval << 4) + numvalue(c);
if (--ndig)
break; /* Might have more digits */
} else {
p--; /* Process this character again */
}
if (unlikely(p <= escp))
EMIT(escp[-1]);
else if (state == st_ucs)
EMIT_UTF8(nval);
else
EMIT(nval);
state = st_start;
break;
default:
panic();
}
}
break;
default:
/* Not a quoted string, just return the input... */
while ((c = *p++))
EMIT(c);
break;
}
/* Zero-terminate the output */
*q = '\0';
if (ctlmask & badctl)
nasm_nonfatal("control character in string not allowed here");
if (ep)
*ep = (char *)p - 1;
return (char *)q - str;
}
#undef EMIT
size_t nasm_unquote(char *str, char **ep)
{
return nasm_unquote_common(str, ep, 0);
}
size_t nasm_unquote_cstr(char *str, char **ep)
{
/*
* These are the only control characters permitted: BEL BS TAB ESC
*/
const uint32_t okctl = (1 << '\a') | (1 << '\b') | (1 << '\t') | (1 << 27);
return nasm_unquote_common(str, ep, ~okctl);
}
/*
* Find the end of a quoted string; returns the pointer to the terminating
* character (either the ending quote or the null character, if unterminated.)
* If the input is not a quoted string, return NULL.
*/
char *nasm_skip_string(const char *str)
{
char bq;
const char *p;
char c;
enum unq_state {
st_start,
st_backslash,
st_done
} state;
bq = str[0];
p = str+1;
switch (bq) {
case '\'':
case '\"':
/* '...' or "..." string */
while ((c = *p++) && (c != bq))
;
break;
case '`':
/* `...` string */
state = st_start;
while (state != st_done) {
c = *p++;
switch (state) {
case st_start:
switch (c) {
case '\\':
state = st_backslash;
break;
case '`':
case '\0':
state = st_done;
break;
default:
break;
}
break;
case st_backslash:
/*
* Note: for the purpose of finding the end of the string,
* all successor states to st_backslash are functionally
* equivalent to st_start, since either a backslash or
* a backquote will force a return to the st_start state.
*/
state = c ? st_start : st_done;
break;
default:
panic();
}
}
break;
default:
/* Not a string at all... */
return NULL;
}
return (char *)p - 1;
}
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