Monday, 12 October 2009

Dumping ACPI tables using acpidump and acpixtract

Most of the time when I'm looking at BIOS issues I just look at the disassembled ACPI DSDT using the following runes:

$ sudo cat /proc/acpi/dsdt > dstd.dat
$ iasl -d dstd.dat

..and look at the disassembly in dstd.dsl

Some BIOS bugs need a little more examination, and that's where I use acpidump + acpixtract. The simplest way to dump all the ACPI tables is as follows:

$ sudo acpidump > acpi.dat
$ acpixtract -a acpi.dat
Acpi table [DSDT] - 24564 bytes written to DSDT.dat
Acpi table [FACS] - 64 bytes written to FACS.dat
Acpi table [FACP] - 244 bytes written to FACP1.dat
Acpi table [APIC] - 104 bytes written to APIC1.dat
Acpi table [HPET] - 56 bytes written to HPET.dat
Acpi table [MCFG] - 60 bytes written to MCFG.dat
Acpi table [TCPA] - 50 bytes written to TCPA.dat
Acpi table [TMOR] - 38 bytes written to TMOR.dat
Acpi table [SLIC] - 374 bytes written to SLIC.dat
Acpi table [APIC] - 104 bytes written to APIC2.dat
Acpi table [BOOT] - 40 bytes written to BOOT.dat
Acpi table [SSDT] - 685 bytes written to SSDT1.dat
Acpi table [SSDT] - 163 bytes written to SSDT2.dat
Acpi table [SSDT] - 607 bytes written to SSDT3.dat
Acpi table [SSDT] - 166 bytes written to SSDT4.dat
Acpi table [SSDT] - 1254 bytes written to SSDT5.dat
Acpi table [XSDT] - 148 bytes written to XSDT.dat
Acpi table [FACP] - 116 bytes written to FACP2.dat
Acpi table [RSDT] - 88 bytes written to RSDT.dat
Acpi table [RSDP] - 36 bytes written to RSDP.dat

..this dumps out all the tables into files.

One can the disassemble the required file using iasl, e.g.:

$ iasl -d APIC1.dat

or decode the table using madt:

$ madt < ACPI1.dsl
ACPI: APIC (v001 INTEL CRESTLNE 0x06040000 LOHR 0x0000005a) @ 0x(nil)
ACPI: LAPIC (acpi_id[0x00] lapic_id[0x00] enabled)
ACPI: LAPIC (acpi_id[0x01] lapic_id[0x01] enabled)
ACPI: IOAPIC (id[0x01] address[0xfec00000] global_irq_base[0x0])
ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 dfl dfl)
ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level)
ACPI: LAPIC_NMI (acpi_id[0x00] high edge lint[0x1])
ACPI: LAPIC_NMI (acpi_id[0x01] high edge lint[0x1])
Length 104 OK
Checksum OK

Or to just get one particular table, I use:

$ sudo acpidump -t SSDT > SSDT.dat
$ acpixtract -a SSDT.dat
$ iasl -d SSDT.dat
Intel ACPI Component Architecture
AML Disassembler version 20090521 [Jun 30 2009]
Copyright (C) 2000 - 2009 Intel Corporation
Supports ACPI Specification Revision 3.0a

Loading Acpi table from file SSDT.dat
Acpi table [SSDT] successfully installed and loaded
Pass 1 parse of [SSDT]
Pass 2 parse of [SSDT]
Parsing Deferred Opcodes (Methods/Buffers/Packages/Regions)
Parsing completed
Disassembly completed, written to "SSDT.dsl"

Armed with a copy of the ACPI spec, one can then start digging into why there are weird Linux/BIOS interactions occurring.


  1. Good article. Thanks for it. I am using stalk kernel 2.6.26 and could not find cat /proc/acpi/dsdt. Any idea how to enable this? Also can I know from where to get the tools you had used to disassemble?


  2. For the utilities on a Ubuntu system:

    acpidump and acpixtract: sudo apt-get install acpidump
    iasl: sudo apt-get install iasl

    you can get the source to acpidump, acpixtra and iasl from

    as for /proc/acp/dsdt, you need CONFIG_ACPI_PROCFS enabled. Hope that helps!

  3. Thanks for your answers. There is a small correction to the link . It should be


  4. Thanks Noel for spotting my typo!

  5. In my case, I have followed everything as mentioned above (first take a dump and then extract) . I am not able to get RSDP.dat.

    Can you let me know what I may be missing? I have already check that CONFIG_ACPI_PROCFS is enabled in kernel.

    FYI : I am using a UEFI Secure Boot install on KVM using OVMF.

  6. Latest kernels have the tables at /sys/firmware/acpi/. Everything else in this article should be the same