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[Bug gdb/9885] field for register names too narrow
- From: "larue at cadence dot com" <sourceware-bugzilla at sourceware dot org>
- To: gdb-prs at sourceware dot org
- Date: Mon, 01 Dec 2014 21:07:04 +0000
- Subject: [Bug gdb/9885] field for register names too narrow
- Auto-submitted: auto-generated
- References: <bug-9885-4717 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=9885
--- Comment #1 from larue at cadence dot com ---
I have recently encountered this problem, and found it is much more severe than
indicated in this bug report. If a register name is > 15 characters then a
negative value is passed to n_spaces(). This causes garbage to be printed, and
occasional crashes of gdb.
This problem still exists in gdb-7.8.1.
The function default_print_one_register_info() calls:
print_spaces_filtered (15 - strlen (name), file);
if the register length is greater than 15, then print_spaces_filtered is called
with a negative value.
The following is a snippet of code from gdb/utils.c. Notice that if n < 0,
then n_spaces returns pointer to potentially unallocated data in the heap.
This sometimes causes a crash in gdb, and garbage is printed in other cases.
char *
n_spaces (int n)
{
char *t;
static char *spaces = 0;
static int max_spaces = -1;
if (n > max_spaces)
{
if (spaces)
xfree (spaces);
spaces = (char *) xmalloc (n + 1);
for (t = spaces + n; t != spaces;)
*--t = ' ';
spaces[n] = '\0';
max_spaces = n;
}
return spaces + max_spaces - n;
}
void
print_spaces_filtered (int n, struct ui_file *stream)
{
fputs_filtered (n_spaces (n), stream);
}
Ideally, gdb should be able to nicely print with arbitrary length register
names, but at a minimum the crash and garbage output should be fixed. A simple
way to do this is to put this check in n_spaces()
char *
n_spaces (int n)
{
char *t;
static char *spaces = 0;
static int max_spaces = -1;
if (n > max_spaces)
{
if (spaces)
xfree (spaces);
spaces = (char *) xmalloc (n + 1);
for (t = spaces + n; t != spaces;)
*--t = ' ';
spaces[n] = '\0';
max_spaces = n;
}
return spaces + max_spaces - n;
}
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