Hi Keith, everybody,
I have encountered the following problems with kdb 2.1 (2.4.18)
when trying to catch I/O port accesses in kdb (both can probably be fixed
easily):
1. This code in kdb/kdb_bp.c:
if (kdba_verify_rw(addr, sizeof(kdb_machinst_t))) {
kdb_printf("Invalid address for breakpoint, ignoring bp command\n");
return(0);
}
forbids to set I/O breakpoints on low ports (e.g. 0x20), because the
address check done by kdba_verify_rw is valid for memory addresses
only. AFAICS, no check whatsoever is necessary for I/O port addresses.
I would submit a patch for this, but the address check must be
postponed after the architecture-dependent parsing, and the information
whether this is an I/O port breakpoint must be passed to the checking
code. I don't know what implications that may have for the
other architectures.
2. The DE flag in the CR4 register must be set (for CPUs that have it)
in order to use I/O breakpoints at all. Otherwise they will be simply
ignored by the CPU.
Thus, a line like
if (cpu_has_de)
set_in_cr4 (X86_CR4_DE);
must be put in kdba_init().
That may not suffice because cpu_init() (kernel/setup.c) clears the DE
bit for each CPU, I don't know which one is called first.
Again, I do not oversee all possible implications, so I do not submit a
patch.
As a hack, I inserted the above line in kdba_installdbreg() after the
line
dr7 |= DR7_GE;
This works fine, I can now trap the I/O accesses I want.
Cheers,
Martin
-- Martin Wilck Phone: +49 5251 8 15113 Fujitsu Siemens Computers Fax: +49 5251 8 20409 Heinz-Nixdorf-Ring 1 mailto:Martin.Wilck@Fujitsu-Siemens.com D-33106 Paderborn http://www.fujitsu-siemens.com/primergy- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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