Hi, On Wed, Nov 05, 2008 at 03:16:52PM +0100, Denys Vlasenko wrote: > Before this patch, -s N shows N+1 chars in strings. > More annoyingly, it shows this for shorter strings: > > write(1, "hi\n"..., 3) = 3 > > After patch: > > write(1, "hi\n", 3) = 3
Thank you. I have looked at the code and found more corner cases where
printstr() and printpathn() may misbehave:
3. printpathn:
$ ln -snf 12345 link && strace -q -s5 -ereadlink readlink link >/dev/null
readlink("link", "12345"..., 64) = 5
1. printstr(tcp, addr, -1):
$ env -i strace -qv -s5 -eexecve /bin/true 12345
execve("/bin/true", ["/bin/"..., "12345"...], []) = 0
2. printstr(tcp, addr, >0) -- the case you are talking about:
$ strace -q -s5 -ewrite echo -n 12345 >/dev/null
write(1, "12345"..., 5) = 5
$ cat write.c
#include <unistd.h>
int main(void){return write(1,"",0)<0;}
$ strace -q -ewrite ./write
write(1, ""..., 0) = 0
Attached patch fixes all these bugs.
OK to apply?
--
ldv
--- strace/util.c
+++ strace/util.c
@@ -407,6 +407,12 @@ unsigned long uid;
static char path[MAXPATHLEN + 1];
+/*
+ * Quote string `instr' of length `size'
+ * Write up to (3 + `size' * 4) bytes to `outstr' buffer.
+ * If `len' < 0, treat `instr' as a NUL-terminated string
+ * and quote at most (`size' - 1) bytes.
+ */
static int
string_quote(const char *instr, char *outstr, int len, int size)
{
@@ -417,12 +423,18 @@ string_quote(const char *instr, char *outstr, int len,
int size)
if (xflag > 1)
usehex = 1;
else if (xflag) {
+ /* Check for presence of symbol which require
+ to hex-quote the whole string. */
for (i = 0; i < size; ++i) {
c = ustr[i];
- if (len < 0 && i == size - 2 && c != '\0')
- ++i;
- if (len < 0 && c == '\0')
- break;
+ /* Check for NUL-terminated string. */
+ if (len < 0) {
+ if (c == '\0')
+ break;
+ /* Quote at most size - 1 bytes. */
+ if (i == size - 1)
+ continue;
+ }
if (!isprint(c) && !isspace(c)) {
usehex = 1;
break;
@@ -433,20 +445,31 @@ string_quote(const char *instr, char *outstr, int len,
int size)
*s++ = '\"';
if (usehex) {
+ /* Hex-quote the whole string. */
for (i = 0; i < size; ++i) {
c = ustr[i];
- if (len < 0 && c == '\0')
- break;
+ /* Check for NUL-terminated string. */
+ if (len < 0) {
+ if (c == '\0')
+ break;
+ /* Quote at most size - 1 bytes. */
+ if (i == size - 1)
+ continue;
+ }
sprintf(s, "\\x%02x", c);
s += 4;
}
} else {
for (i = 0; i < size; ++i) {
c = ustr[i];
- if (len < 0 && i == size - 2 && c != '\0')
- ++i;
- if (len < 0 && c == '\0')
- break;
+ /* Check for NUL-terminated string. */
+ if (len < 0) {
+ if (c == '\0')
+ break;
+ /* Quote at most size - 1 bytes. */
+ if (i == size - 1)
+ continue;
+ }
switch (c) {
case '\"': case '\\':
*s++ = '\\';
@@ -495,18 +518,25 @@ string_quote(const char *instr, char *outstr, int len,
int size)
return i == size;
}
+/*
+ * Print path string specified by address `addr' and length `n'.
+ * If path length exceeds `n', append `...' to the output.
+ */
void
printpathn(struct tcb *tcp, long addr, int n)
{
- if (n > sizeof path - 1)
- n = sizeof path - 1;
-
- if (addr == 0) {
+ if (!addr) {
tprintf("NULL");
return;
}
+ /* Cap path length to the path buffer size,
+ and NUL-terminate the buffer. */
+ if (n > sizeof path - 1)
+ n = sizeof path - 1;
path[n] = '\0';
+
+ /* Fetch one byte more to find out whether path length > n. */
if (umovestr(tcp, addr, n + 1, path) < 0)
tprintf("%#lx", addr);
else {
@@ -515,7 +545,8 @@ printpathn(struct tcb *tcp, long addr, int n)
if (trunc)
path[n] = '\0';
- if (string_quote(path, outstr, -1, n + 1) || trunc)
+ (void) string_quote(path, outstr, -1, n + 1);
+ if (trunc)
strcat(outstr, "...");
tprintf("%s", outstr);
}
@@ -527,6 +558,11 @@ printpath(struct tcb *tcp, long addr)
printpathn(tcp, addr, sizeof path - 1);
}
+/*
+ * Print string specified by address `addr' and length `len'.
+ * If `len' < 0, treat the string as a NUL-terminated string.
+ * If string length exceeds `max_strlen', append `...' to the output.
+ */
void
printstr(struct tcb *tcp, long addr, int len)
{
@@ -538,32 +574,39 @@ printstr(struct tcb *tcp, long addr, int len)
tprintf("NULL");
return;
}
- if (!str) {
- if ((str = malloc(max_strlen + 1)) == NULL
- || (outstr = malloc(4*max_strlen
- + sizeof "\"\"...")) == NULL) {
- fprintf(stderr, "out of memory\n");
- tprintf("%#lx", addr);
- return;
- }
+ /* Allocate static buffers if they are not allocated yet. */
+ if (!str)
+ str = malloc(max_strlen + 1);
+ if (!outstr)
+ outstr = malloc(4 * max_strlen + sizeof "\"...\"");
+ if (!str || !outstr) {
+ fprintf(stderr, "out of memory\n");
+ tprintf("%#lx", addr);
+ return;
}
if (len < 0) {
+ /*
+ * Treat as a NUL-terminated string: fetch one byte more
+ * because string_quote() quotes one byte less.
+ */
size = max_strlen + 1;
+ str[max_strlen] = '\0';
if (umovestr(tcp, addr, size, str) < 0) {
tprintf("%#lx", addr);
return;
}
}
else {
- size = MIN(len, max_strlen + 1);
+ size = MIN(len, max_strlen);
if (umoven(tcp, addr, size, str) < 0) {
tprintf("%#lx", addr);
return;
}
}
- if (string_quote(str, outstr, len, size))
+ if (string_quote(str, outstr, len, size) &&
+ (len < 0 || len > max_strlen))
strcat(outstr, "...");
tprintf("%s", outstr);
pgpwOVTmrw5BB.pgp
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