fix null pointer subtraction and comparison in stdio

morally, for null pointers a and b, a-b, a<b, and a>b should all be
defined as 0; however, C does not define any of them.

the stdio implementation makes heavy use of such pointer comparison
and subtraction for buffer logic, and also uses null pos/base/end
pointers to indicate that the FILE is not in the corresponding (read
or write) mode ready for accesses through the buffer.

all of the comparisons are fixed trivially by using != in place of the
relational operators, since the opposite relation (e.g. pos>end) is
logically impossible. the subtractions have been reviewed to check
that they are conditional the stream being in the appropriate reading-
or writing-through-buffer mode, with checks added where needed.

in fgets and getdelim, the checks added should improve performance for
unbuffered streams by avoiding a do-nothing call to memchr, and should
be negligible for buffered streams.

diff --git a/src/internal/stdio_impl.h b/src/internal/stdio_impl.h
index 4afb7ea..8c81fd5 100644 (file)
--- a/src/internal/stdio_impl.h
+++ b/src/internal/stdio_impl.h
@@ -100,10 +100,10 @@ hidden void __getopt_msg(const char *, const char *, const char *, size_t);
 #define ferror(f) ((f)->flags & F_ERR)
 
 #define getc_unlocked(f) \
-       ( ((f)->rpos < (f)->rend) ? *(f)->rpos++ : __uflow((f)) )
+       ( ((f)->rpos != (f)->rend) ? *(f)->rpos++ : __uflow((f)) )
 
 #define putc_unlocked(c, f) \
-       ( ((unsigned char)(c)!=(f)->lbf && (f)->wpos<(f)->wend) \
+       ( ((unsigned char)(c)!=(f)->lbf && (f)->wpos!=(f)->wend) \
        ? *(f)->wpos++ = (c) : __overflow((f),(c)) )
 
 /* Caller-allocated FILE * operations */

diff --git a/src/stdio/__overflow.c b/src/stdio/__overflow.c
index 3bb3792..e65a594 100644 (file)
--- a/src/stdio/__overflow.c
+++ b/src/stdio/__overflow.c
@@ -4,7 +4,7 @@ int __overflow(FILE *f, int _c)
 {
        unsigned char c = _c;
        if (!f->wend && __towrite(f)) return EOF;
-       if (f->wpos < f->wend && c != f->lbf) return *f->wpos++ = c;
+       if (f->wpos != f->wend && c != f->lbf) return *f->wpos++ = c;
        if (f->write(f, &c, 1)!=1) return EOF;
        return c;
 }

diff --git a/src/stdio/__stdio_exit.c b/src/stdio/__stdio_exit.c
index 5741070..a5e42c6 100644 (file)
--- a/src/stdio/__stdio_exit.c
+++ b/src/stdio/__stdio_exit.c
@@ -9,8 +9,8 @@ static void close_file(FILE *f)
 {
        if (!f) return;
        FFINALLOCK(f);
-       if (f->wpos > f->wbase) f->write(f, 0, 0);
-       if (f->rpos < f->rend) f->seek(f, f->rpos-f->rend, SEEK_CUR);
+       if (f->wpos != f->wbase) f->write(f, 0, 0);
+       if (f->rpos != f->rend) f->seek(f, f->rpos-f->rend, SEEK_CUR);
 }
 
 void __stdio_exit(void)

diff --git a/src/stdio/__toread.c b/src/stdio/__toread.c
index 309ee6e..f142ff0 100644 (file)
--- a/src/stdio/__toread.c
+++ b/src/stdio/__toread.c
@@ -3,7 +3,7 @@
 int __toread(FILE *f)
 {
        f->mode |= f->mode-1;
-       if (f->wpos > f->wbase) f->write(f, 0, 0);
+       if (f->wpos != f->wbase) f->write(f, 0, 0);
        f->wpos = f->wbase = f->wend = 0;
        if (f->flags & F_NORD) {
                f->flags |= F_ERR;

diff --git a/src/stdio/ext2.c b/src/stdio/ext2.c
index afd8b34..3416278 100644 (file)
--- a/src/stdio/ext2.c
+++ b/src/stdio/ext2.c
@@ -3,14 +3,13 @@
 
 size_t __freadahead(FILE *f)
 {
-       return f->rend - f->rpos;
+       return f->rend ? f->rend - f->rpos : 0;
 }
 
 const char *__freadptr(FILE *f, size_t *sizep)
 {
-       size_t size = f->rend - f->rpos;
-       if (!size) return 0;
-       *sizep = size;
+       if (f->rpos == f->rend) return 0;
+       *sizep = f->rend - f->rpos;
        return (const char *)f->rpos;
 }
 

diff --git a/src/stdio/fflush.c b/src/stdio/fflush.c
index bf1e843..02dae27 100644 (file)
--- a/src/stdio/fflush.c
+++ b/src/stdio/fflush.c
@@ -11,7 +11,7 @@ int fflush(FILE *f)
 
                for (f=*__ofl_lock(); f; f=f->next) {
                        FLOCK(f);
-                       if (f->wpos > f->wbase) r |= fflush(f);
+                       if (f->wpos != f->wbase) r |= fflush(f);
                        FUNLOCK(f);
                }
                __ofl_unlock();
@@ -22,7 +22,7 @@ int fflush(FILE *f)
        FLOCK(f);
 
        /* If writing, flush output */
-       if (f->wpos > f->wbase) {
+       if (f->wpos != f->wbase) {
                f->write(f, 0, 0);
                if (!f->wpos) {
                        FUNLOCK(f);
@@ -31,7 +31,7 @@ int fflush(FILE *f)
        }
 
        /* If reading, sync position, per POSIX */
-       if (f->rpos < f->rend) f->seek(f, f->rpos-f->rend, SEEK_CUR);
+       if (f->rpos != f->rend) f->seek(f, f->rpos-f->rend, SEEK_CUR);
 
        /* Clear read and write modes */
        f->wpos = f->wbase = f->wend = 0;

diff --git a/src/stdio/fgetln.c b/src/stdio/fgetln.c
index afe12b5..5748435 100644 (file)
--- a/src/stdio/fgetln.c
+++ b/src/stdio/fgetln.c
@@ -8,7 +8,7 @@ char *fgetln(FILE *f, size_t *plen)
        ssize_t l;
        FLOCK(f);
        ungetc(getc_unlocked(f), f);
-       if ((z=memchr(f->rpos, '\n', f->rend - f->rpos))) {
+       if (f->rend && (z=memchr(f->rpos, '\n', f->rend - f->rpos))) {
                ret = (char *)f->rpos;
                *plen = ++z - ret;
                f->rpos = (void *)z;

diff --git a/src/stdio/fgets.c b/src/stdio/fgets.c
index d3f9819..6171f39 100644 (file)
--- a/src/stdio/fgets.c
+++ b/src/stdio/fgets.c
@@ -21,14 +21,16 @@ char *fgets(char *restrict s, int n, FILE *restrict f)
        }
 
        while (n) {
-               z = memchr(f->rpos, '\n', f->rend - f->rpos);
-               k = z ? z - f->rpos + 1 : f->rend - f->rpos;
-               k = MIN(k, n);
-               memcpy(p, f->rpos, k);
-               f->rpos += k;
-               p += k;
-               n -= k;
-               if (z || !n) break;
+               if (f->rpos != f->rend) {
+                       z = memchr(f->rpos, '\n', f->rend - f->rpos);
+                       k = z ? z - f->rpos + 1 : f->rend - f->rpos;
+                       k = MIN(k, n);
+                       memcpy(p, f->rpos, k);
+                       f->rpos += k;
+                       p += k;
+                       n -= k;
+                       if (z || !n) break;
+               }
                if ((c = getc_unlocked(f)) < 0) {
                        if (p==s || !feof(f)) s = 0;
                        break;

diff --git a/src/stdio/fgetwc.c b/src/stdio/fgetwc.c
index 07fb6d7..0801e28 100644 (file)
--- a/src/stdio/fgetwc.c
+++ b/src/stdio/fgetwc.c
@@ -10,7 +10,7 @@ static wint_t __fgetwc_unlocked_internal(FILE *f)
        size_t l;
 
        /* Convert character from buffer if possible */
-       if (f->rpos < f->rend) {
+       if (f->rpos != f->rend) {
                l = mbtowc(&wc, (void *)f->rpos, f->rend - f->rpos);
                if (l+1 >= 1) {
                        f->rpos += l + !l; /* l==0 means 1 byte, null */

diff --git a/src/stdio/fread.c b/src/stdio/fread.c
index 733d371..a2116da 100644 (file)
--- a/src/stdio/fread.c
+++ b/src/stdio/fread.c
@@ -13,7 +13,7 @@ size_t fread(void *restrict destv, size_t size, size_t nmemb, FILE *restrict f)
 
        f->mode |= f->mode-1;
 
-       if (f->rend - f->rpos > 0) {
+       if (f->rpos != f->rend) {
                /* First exhaust the buffer. */
                k = MIN(f->rend - f->rpos, l);
                memcpy(dest, f->rpos, k);

diff --git a/src/stdio/fseek.c b/src/stdio/fseek.c
index 67d75f7..439308f 100644 (file)
--- a/src/stdio/fseek.c
+++ b/src/stdio/fseek.c
@@ -3,10 +3,10 @@
 int __fseeko_unlocked(FILE *f, off_t off, int whence)
 {
        /* Adjust relative offset for unread data in buffer, if any. */
-       if (whence == SEEK_CUR) off -= f->rend - f->rpos;
+       if (whence == SEEK_CUR && f->rend) off -= f->rend - f->rpos;
 
        /* Flush write buffer, and report error on failure. */
-       if (f->wpos > f->wbase) {
+       if (f->wpos != f->wbase) {
                f->write(f, 0, 0);
                if (!f->wpos) return -1;
        }

diff --git a/src/stdio/ftell.c b/src/stdio/ftell.c
index 5ca4165..1a2afbb 100644 (file)
--- a/src/stdio/ftell.c
+++ b/src/stdio/ftell.c
@@ -5,12 +5,16 @@
 off_t __ftello_unlocked(FILE *f)
 {
        off_t pos = f->seek(f, 0,
-               (f->flags & F_APP) && f->wpos > f->wbase
+               (f->flags & F_APP) && f->wpos != f->wbase
                ? SEEK_END : SEEK_CUR);
        if (pos < 0) return pos;
 
        /* Adjust for data in buffer. */
-       return pos - (f->rend - f->rpos) + (f->wpos - f->wbase);
+       if (f->rend)
+               pos += f->rpos - f->rend;
+       else if (f->wbase)
+               pos += f->wpos - f->wbase;
+       return pos;
 }
 
 off_t __ftello(FILE *f)

diff --git a/src/stdio/getdelim.c b/src/stdio/getdelim.c
index 60c6cc1..c313775 100644 (file)
--- a/src/stdio/getdelim.c
+++ b/src/stdio/getdelim.c
@@ -25,8 +25,13 @@ ssize_t getdelim(char **restrict s, size_t *restrict n, int delim, FILE *restric
        if (!*s) *n=0;
 
        for (;;) {
-               z = memchr(f->rpos, delim, f->rend - f->rpos);
-               k = z ? z - f->rpos + 1 : f->rend - f->rpos;
+               if (f->rpos != f->rend) {
+                       z = memchr(f->rpos, delim, f->rend - f->rpos);
+                       k = z ? z - f->rpos + 1 : f->rend - f->rpos;
+               } else {
+                       z = 0;
+                       k = 0;
+               }
                if (i+k+1 >= *n) {
                        if (k >= SIZE_MAX/2-i) goto oom;
                        size_t m = i+k+2;

diff --git a/src/stdio/vfwscanf.c b/src/stdio/vfwscanf.c
index 7be6634..82f4860 100644 (file)
--- a/src/stdio/vfwscanf.c
+++ b/src/stdio/vfwscanf.c
@@ -76,7 +76,7 @@ static int in_set(const wchar_t *set, int c)
 #if 1
 #undef getwc
 #define getwc(f) \
-       ((f)->rpos < (f)->rend && *(f)->rpos < 128 ? *(f)->rpos++ : (getwc)(f))
+       ((f)->rpos != (f)->rend && *(f)->rpos < 128 ? *(f)->rpos++ : (getwc)(f))
 
 #undef ungetwc
 #define ungetwc(c,f) \