[docs] add debug support for GBL doc
Adding a document for how to debug GBL with UEFI debug support protocol. Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
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Ying-Chun Liu (PaulLiu)
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Kelvin Zhang
Kelvin Zhang
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docs/gdb_debug_support_for_gbl.md
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docs/gdb_debug_support_for_gbl.md
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# GDB debug support for GBL in LK
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## Overview
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This document describes how to use GDB to debug GBL and using the UEFI
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debug support protocol.
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## Build GBL
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First, we need to build the GBL with the following steps.
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### Download GBL
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* GBL_MANIFEST_URL_DEFAULT="https://android.googlesource.com/kernel/manifest/"
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* GBL_MANIFEST_BRANCH_DEFAULT="uefi-gbl-mainline"
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* mkdir -p gbl
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* cd gbl
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* repo init -u ${GBL_MANIFEST_URL} -b ${GBL_MANIFEST_BRANCH}
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* repo sync
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### Build GBL with Debug Target
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* REPO_ROOT=$(readlink -f .)
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* BAZEL_TARGET="@gbl//efi:aarch64_debug_dev"
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* BAZEL_OUT_BASE="${REPO_ROOT}/out_aarch64_debug_dev"
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* # Build GBL
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* "${REPO_ROOT}/tools/bazel" "--output_base=${BAZEL_OUT_BASE}" build "${BAZEL_TARGET}" --sandbox_debug --verbose_failures --symlink_prefix=/
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* # Copy GBL out of the directory
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* BAZEL_OUT_BIN=$("${REPO_ROOT}/tools/bazel" cquery "${BAZEL_TARGET}" --output files 2>/dev/null)
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* BAZEL_OUT_BIN=$(readlink -f "${BAZEL_OUT_BASE}/execroot/_main/${BAZEL_OUT_BIN}")
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* GBL_DBG_BIN="${BAZEL_OUT_BASE}/gbl.efi"
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* cp "${BAZEL_OUT_BIN}" "${GBL_DBG_BIN}"
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* # pack debug symbols
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* DWO_OUT="${BAZEL_OUT_BASE}/dwo"
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* mkdir -p "${DWO_OUT}"
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* find "${BAZEL_OUT_BASE}" -name *.dwo -not -path "${DWO_OUT}*" -exec mv -f {} "${DWO_OUT}"/ \; 2>/dev/null || true
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* llvm-dwp -o "${GBL_DBG_BIN}.dwp" $(ls "${DWO_OUT}"/*.dwo)
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## Run LK with QEmu and load GBL.
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### Run qemu
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* APP1=/path/to/gbl.efi
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* qemu-system-aarch64 -machine virt \
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-m 1024M \
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-cpu cortex-a57 \
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-nographic \
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-kernel build-qemu-virt-arm64-test/lk.elf \
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-drive if=none,file=${APP1},id=blk1,format=raw \
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-gdb tcp::13333
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### Run GBL
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In the LK prompt. Use the following commands.
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* uefi_set_var gbl_debug 1
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* uefi_load virtio0
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And we will see the following message.
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```
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bio_read returns 4096, took 5 msecs (819200 bytes/sec)
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PE header machine type: aa64
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Valid UEFI application found.
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Failed to allocate physical memory size 7073792 at specified address 0x140000000 fallback to regular allocation
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Relocating image from 0x140000000 to 0x53600000
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Entry function located at 0x53604db0
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platform_setup_system_table is called
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Calling kernel with stack [0x54800000, 0x548fffff]
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locate_handle_buffer(0x2, (0x3152bca5 0xeade 0x433d 0x441f29dc1cc02e86), search_key=0)
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Required protocol not found: EfiRngProtocol
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SECURITY WARNING: Failed to generate stack canary, using static default: Unsupported
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open_protocol(LOADED_IMAGE_PROTOCOL_GUID, handle=0x53600000, agent_handle=0x53600000, controller_handle=0, attr=0x1)
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Image base: 0x53600000
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Please run load_gbl_debug_bin.py or set $x0=0 from gdb to continue.
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```
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## Use GDB to debug.
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### Use GDB to load debug symbols of GBL manually.
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Since GBL prints its own address. We can load the debug symbols based on
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that address.
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The above shows the Image base address is 0x53600000
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We can use the command "readpe gbl.efi". Look at the "Virtual Address" field.
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And we can get the following offsets.
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* .text: 0x1000
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* .data: 0x392000
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* .rdata: 0x315000
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So the actual address is by adding the base address (0x53600000)
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to each of the address above. Then it becomes:
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* .text: 0x53601000
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* .data: 0x53992000
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* .rdata: 0x53915000
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Then we can run "gdb-multiarch". In the GDB prompt we use the following
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commands.
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* target remote :13333
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* add-symbol-file /path/to/gbl.efi 0x53601000 -s .data 0x53992000 -s .rdata 0x53915000
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And use "bt full" we can see the following output.
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```
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#0 0x0000000053604d7c in app::wait_gdb (entry=0x548ffe30)
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at external/gbl/efi/app/main.rs:145
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buf = [49]
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image_base = 1398800384
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#1 0x0000000053604e80 in app::efi_main (image_handle=0x53600000,
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systab_ptr=0x5340f000) at external/gbl/efi/app/main.rs:184
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canary = 2812601071695653757
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entry = efi::EfiEntry {image_handle: 0x53600000, systab_ptr: 0x5340f000}
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#2 0xffff00000012dcfc in ?? ()
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No symbol table info available.
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#3 0xffff00000012ab10 in ?? ()
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No symbol table info available.
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Backtrace stopped: previous frame inner to this frame (corrupt stack?)
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```
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Then we can use "set $x0=0" in GDB to let the GBL continue to run.
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### Use UEFI Debug support protocol.
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By loading python extensions we made, we can make the above things easier.
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In GDB, we load the python extension.
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* target remote :13333
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* source gdb_efi_apps.py
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And we will have several "efi" commands.
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* efi showvendor # show the vendor of the bootloader.
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* efi table # show the configuration tables of the UEFI
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* efi test list # list of the current loading UEFI apps
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* efi loadsymbols # load debug symbols
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```
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(gdb) efi showvendor
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Firmware Vendor: Little Kernel
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Firmware Version: 0
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(gdb) efi table
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1CE1E5BC-7CEB-42F2-81E5-8AADF180F57B: VendorTable = 0x53411000
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B1B621D5-F19C-41A5-830B-D9152C69AAE0: VendorTable = 0x53412000
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gEfiDebugImageInfoTableGuid: VendorTable = 0xffff0000001767a8
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(gdb) efi test list
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\virtio0: addr: 0x53600000, size: 0x6bf000, path:None
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(gdb) efi loadsymbols -m virtio0 /path/to/gbl.efi /path/to/gbl.efi
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LoadedImage address: 0x53600000, size: 0x6bf000
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PE text offset: 0x1000
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PE data offset: 0x392000
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PE rdata offset: 0x315000
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(gdb) bt full
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#0 0x0000000053604d7c in app::wait_gdb (entry=0x548ffe30)
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at external/gbl/efi/app/main.rs:145
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buf = [49]
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image_base = 1398800384
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#1 0x0000000053604e80 in app::efi_main (image_handle=0x53600000,
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systab_ptr=0x5340f000) at external/gbl/efi/app/main.rs:184
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canary = 2812601071695653757
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entry = efi::EfiEntry {image_handle: 0x53600000, systab_ptr: 0x5340f000}
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#2 0xffff00000012dcfc in ?? ()
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No symbol table info available.
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#3 0xffff00000012ab10 in ?? ()
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No symbol table info available.
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Backtrace stopped: previous frame inner to this frame (corrupt stack?)
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```
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The GDB python extension is currently put here.
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* https://git.codelinaro.org/paul_liu/test-e5e925b80fd7/-/blob/clo/main/verify_gbl_on_qemu/gdb_efi_apps.py?ref_type=heads
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It needs EDK2's python extension scritps. And we are currently trying
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to upstream this extension to EDK2.
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* https://github.com/tianocore/edk2/pull/11285
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