Debugging
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Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!
GDB Interface
coreboot has an easy to use interface to the GNU debugger gdb. To enable it, add the following two lines to your mainboard's Options.lb:
uses CONFIG_GDB_STUB ... default CONFIG_GDB_STUB=1
NOTE: You need to put the uses line into the uses-section of the Options.lb, and the default line into the configuration section, or the coreboot config tool will print an error.
Compiling coreboot with debugging symbols might help:
Index: src/config/Config.lb =================================================================== --- src/config/Config.lb (revision 1578) +++ src/config/Config.lb (working copy) @@ -10,7 +10,7 @@ makedefine GCC_INC_DIR := $(shell LC_ALL=C $(GCC) -print-search-dirs | sed -ne "s/install: \(.*\)/\1include/gp") makedefine CPPFLAGS := -I$(TOP)/src/include -I$(TOP)/src/arch/$(ARCH)/include -I$(GCC_INC_DIR) $(CPUFLAGS) -makedefine CFLAGS := $(CPU_OPT) $(DISTRO_CFLAGS) $(CPPFLAGS) -Os -nostdinc -nostdlib -Wall -Wundef ... +makedefine CFLAGS := $(CPU_OPT) $(DISTRO_CFLAGS) $(CPPFLAGS) -O2 -g -nostdinc -nostdlib -Wall -Wundef ... if ASSEMBLER_DEBUG makedefine DEBUG_CFLAGS := -g -dA -fverbose-asm
Then you will not get exceptions like this:
Unexpected Exception: 0 @ 10:0012724b - Halting Code: 0 eflags: 00010046 eax: 00000001 ebx: 00000061 ecx: 00000004 edx: 00000000 edi: 00000000 esi: 00000061 ebp: 00163abc esp: 00163a98
But instead you will be able to connect to the machine using gdb over a serial line in case of an exception:
(gdb) file coreboot-v2/coreboot-builds/kontron_986lcd-m/fallback/coreboot_ram
Reading symbols from coreboot-v2/coreboot-builds/kontron_986lcd-m/fallback/coreboot_ram...done.
(gdb) set remotebaud 115200
(gdb) target remote /dev/ttyUSB0
Remote debugging using /dev/ttyUSB0
0x0012824b in __udivdi3 (n=17082841390, d=0) at ...
...
(gdb) bt
#0 0x0012824b in __udivdi3 (n=17082841390, d=0)
at /usr/lib/gcc/gcc- 4.3.2/libgcc/../gcc/libgcc2.c:899
#1 0x0011efa2 in handle_port_61h ()
#2 0x0011fbc3 in my_inb ()
#3 0x001189f5 in x86emuOp_in_byte_AL_IMM ()
#4 0x001092f1 in X86EMU_exec ()
#5 0x0010a06f in biosemu ()
#6 0x0011fcfb in run_bios ()
#7 0x0010cbcb in pci_dev_init ()
#8 0x00103d9b in dev_initialize ()
#9 0x0010f8b5 in hardwaremain ()
#10 0x00100099 in _text ()