Aha – whilst what I’ve written below is true, it doesn’t accurately reflect the issue.
If I start Wireshark and double click on a file in the recently opened list, part of the processing is this:
cf_open() calls
ws_epan_new() calls
epan_new() calls
init_dissection() calls
wmem_enter_file_scope() which sets
file_scope->in_scope = TRUE;
All of the above takes place before my new block reader is called.
If I start Wireshark, use Ctl-O and then double click on a file in the file explorer dialogue, there is no call to wmem_enter_file_scope() before my block reader is called.
I believe this is a bug. The two file opens should be consistent in the setting of file_scope->in_scope = TRUE, and hence the scope of wmem_file_scope().
- Am I wrong?
- Have I missed something?
- Should I create a bug report?
Thanks and regards…Paul
From: Paul Offord
Sent: 25 March 2018 10:31
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: allocator->in_scope
Hi,
Still working on my new block reader. To recap, I’ve defined a new pcapng block type and written a dissector. The first thing I have to do is read the new block type, and Wireshark provides a framework to do this. In the new block reader
I define some space like this:
tdb_namespace = wmem_strdup_printf(wmem_file_scope(), "%s", option_block->option_data);
Eventually the wmem_strdup_printf(…) execution calls this function:
void *
wmem_alloc(wmem_allocator_t *allocator, const size_t size)
{
if (allocator == NULL) {
return g_malloc(size);
}
if (!allocator->in_scope) // debug code
while (FALSE); // debug code
g_assert(allocator->in_scope);
if (size == 0) {
return NULL;
}
return allocator->walloc(allocator->private_data, size);
}
The g_assert intermittently fails. If I open one file containing the new block, allocator->in_scope is true. If I call another it’s false.
The block read is called before we start dissecting the contents with the dissector code.
- At what point is wmem_file_scope in scope?
- Should it be when my block reader is called or is it only guaranteed when the dissector code is called?
Thanks and regards…Paul
