Debugging session with qemu and u-boot

[A2va]

Hello !
I want to debug a program that is loaded by u-boot and run under qemu. So in the u-boot I do:

setenv hello "tftp x86/hello_world.bin" run hello go 0x40000 

For now, I have this launch.json configuration:

{ "name": "Debug", "type": "gdb", "request": "attach", "executable": "${workspaceFolder}/x86/hello_world.bin", "target": "localhost:1234", "remote": true, "stopAtEntry": true, "cwd": "${workspaceRoot}", "debugger_args": ["-ix", "${workspaceFolder}/gdbinit"], "gdbpath": "/opt/toolchains/i686-linux_6.4.0/bin/i686-linux-gdb", "printCalls": true, "showDevDebugOutput": true }

Qemu launch script:

#!/bin/bash qemu/i386-softmmu/qemu-system-i386 $1 -s \	-M pc -cpu Haswell -bios qemu/coreboot.rom \	-serial mon:stdio \	-m 256 \ -netdev user,id=n0,tftp=. \	-device e1000e,netdev=n0,mac=00:01:29:53:97:BA \	-nographic 

Logs:

1-gdb-set target-async on 2-list-features 3-environment-directory "/home/reds/asm/asm_lab02" 4-target-select remote localhost:1234 GDB -> App: {"outOfBandRecord":[{"isStream":false,"type":"notify","asyncClass":"thread-group-added","output":[["id","i1"]]}]} GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"log","content":"\"/home/reds/asm/asm_lab02/x86/hello_world.bin\": not in executable format: File format not recognized\n"}]} "/home/reds/asm/asm_lab02/x86/hello_world.bin": not in executable format: File format not recognized GDB -> App: {"token":1,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[]}} GDB -> App: {"token":2,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["features",["frozen-varobjs","pending-breakpoints","thread-info","data-read-memory-bytes","breakpoint-notifications","ada-task-info","language-option","info-gdb-mi-command","undefined-command-error-code","exec-run-start-option"]]]}} GDB -> App: {"token":3,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["source-path","/home/reds/asm/asm_lab02:$cdir:$cwd"]]}} GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"log","content":"warning: while parsing target description (at line 1): Target description specified unknown architecture \"arm\"\n"}]} warning: while parsing target description (at line 1): Target description specified unknown architecture "arm" GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"log","content":"warning: Could not load XML target description; ignoring\n"}]} warning: Could not load XML target description; ignoring GDB -> App: {"outOfBandRecord":[{"isStream":false,"type":"notify","asyncClass":"thread-group-started","output":[["id","i1"],["pid","1"]]}]} GDB -> App: {"outOfBandRecord":[{"isStream":false,"type":"notify","asyncClass":"thread-created","output":[["id","1"],["group-id","i1"]]}]} GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"console","content":"0x9ffe8c70 in ?? ()\n"}]} 0x9ffe8c70 in ?? () GDB -> App: {"outOfBandRecord":[{"isStream":false,"type":"exec","asyncClass":"stopped","output":[["frame",[["addr","0x9ffe8c70"],["func","??"],["args",[]]]],["thread-id","1"],["stopped-threads","all"]]}]} GDB -> App: {"token":4,"outOfBandRecord":[],"resultRecords":{"resultClass":"connected","results":[]}} 5-thread-info 6-break-insert -f "/home/reds/asm/asm_lab02/x86/hello_world.c:31" GDB -> App: {"token":5,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["threads",[[["id","1"],["target-id","Thread 1.1"],["details","CPU#0 [running]"],["frame",[["level","0"],["addr","0x9ffe8c70"],["func","??"],["args",[]]]],["state","stopped"]]]],["current-thread-id","1"]]}} GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"log","content":"No symbol table is loaded. Use the \"file\" command.\n"}]} No symbol table is loaded. Use the "file" command. GDB -> App: {"token":6,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["bkpt",[["number","1"],["type","breakpoint"],["disp","keep"],["enabled","y"],["addr","<PENDING>"],["pending","/home/reds/asm/asm_lab02/x86/hello_world.c:31"],["times","0"],["original-location","/home/reds/asm/asm_lab02/x86/hello_world.c:31"]]]]}} 7-thread-info GDB -> App: {"token":7,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["threads",[[["id","1"],["target-id","Thread 1.1"],["details","CPU#0 [running]"],["frame",[["level","0"],["addr","0x9ffe8c70"],["func","??"],["args",[]]]],["state","stopped"]]]],["current-thread-id","1"]]}} 8-stack-info-depth --thread 1 GDB -> App: {"token":8,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["depth","1"]]}} 9-stack-list-frames --thread 1 0 0 GDB -> App: {"token":9,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["stack",[["frame",[["level","0"],["addr","0x9ffe8c70"],["func","??"]]]]]]}} 10-break-insert -t -f main 11-exec-continue GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"log","content":"No symbol table is loaded. Use the \"file\" command.\n"}]} No symbol table is loaded. Use the "file" command. GDB -> App: {"token":10,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[["bkpt",[["number","2"],["type","breakpoint"],["disp","del"],["enabled","y"],["addr","<PENDING>"],["pending","main"],["times","0"],["original-location","main"]]]]}} GDB -> App: {"token":11,"outOfBandRecord":[],"resultRecords":{"resultClass":"running","results":[]}} GDB -> App: {"outOfBandRecord":[{"isStream":false,"type":"exec","asyncClass":"running","output":[["thread-id","all"]]}]} 12-stack-info-depth --thread 1 GDB -> App: {"token":12,"outOfBandRecord":[],"resultRecords":{"resultClass":"error","results":[["msg","Selected thread is running."]]}} 13-thread-info GDB -> App: {"token":13,"outOfBandRecord":[],"resultRecords":{"resultClass":"error","results":[["msg","Cannot execute this command while the target is running.\nUse the \"interrupt\" command to stop the target\nand then try again."]]}} 

Why it doesn't work ?

[GitMensch]

The biggest part is likely this line:

GDB -> App: {"outOfBandRecord":[{"isStream":true,"type":"log","content":""/home/reds/asm/asm_lab02/x86/hello_world.bin": not in executable format: File format not recognized\n"}]}
"/home/reds/asm/asm_lab02/x86/hello_world.bin": not in executable format: File format not recognized

So the GDB you use cannot understand the binary you told it to debug.

[A2va]

So the GDB you use cannot understand the binary you told it to debug.
This is strange because this gdb is in the same place as the gcc that built the program.

Anyway, if that helps, here's the makefile (I didn't write it, it was provided):

########################################################################## ############# # Toolchain # ############# TOOL_PREFIX:= i686-linux AR = $(TOOL_PREFIX)-ar LD = $(TOOL_PREFIX)-ld AS = $(TOOL_PREFIX)-as CC = $(TOOL_PREFIX)-gcc OBJCOPY = $(TOOL_PREFIX)-objcopy OBJDUMP = $(TOOL_PREFIX)-objdump CPP = $(CC) -E ######################################################################### ################# # General flags # ################# # (preprocessor flags) # GCC include directory (of specific toolchain) gccincdir := $(shell $(CC) -print-file-name=include) # Debug and Disable optimisation CPPFLAGS += -g -O0 # 32-bit Architecture CPPFLAGS += -march=i386 -mpreferred-stack-boundary=2 # Warn on everything CPPFLAGS += -Wall # Include directories (do not use default system directories for header files) CPPFLAGS += -nostdinc -I../u-boot/include -I../u-boot/arch/x86/include -isystem $(gccincdir) # For calls to u-boot functions CPPFLAGS += -D__KERNEL__ -DREALMODE_BASE=0x7c0 -DCONFIG_X86 -D__I386__ # Emit DWARF unwind info as compiler generated .eh_frame section instead of using GAS .cfi_* directives. CPPFLAGS += -fno-dwarf2-cfi-asm # A unit compiled with -fstack-usage will generate an extra file that specifies # the maximum amount of stack used, on a per-function basis. The file has the # same basename as the target object file with a .su extension. Each line of # this file is made up of three fields: # * The name of the function. # * A number of bytes. # * One or more qualifiers: static, dynamic, bounded. The second field # corresponds to the size of the known part of the function frame. The # qualifier static means that the function frame size is purely static. It # usually means that all local variables have a static size. In this case, the # second field is a reliable measure of the function stack utilization. The # qualifier dynamic means that the function frame size is not static. It # happens mainly when some local variables have a dynamic size. When this # qualifier appears alone, the second field is not a reliable measure of the # function stack analysis. When it is qualified with bounded, it means that # the second field is a reliable maximum of the function stack utilization. A # unit compiled with -Wstack-usage will issue a warning for each subprogram # whose stack usage might be larger than the specified amount of bytes. The # wording is in keeping with the qualifier documented above. CPPFLAGS += -fstack-usage # Don't append extra code for stack protection CPPFLAGS += -fno-stack-protector # Do not reorder top-level functions, variables, and asm statements CPPFLAGS += -fno-toplevel-reorder # https://interrupt.memfault.com/blog/best-and-worst-gcc-clang-compiler-flags#-ffunction-sections--fdata-sections----gc-sections # Give each function its own section CPPFLAGS += -ffunction-sections # A freestanding environment is one in which the standard library may not exist, # and program startup may not necessarily be at "main". The option -ffreestanding # directs the compiler to not assume that standard functions have their usual definition. CPPFLAGS += -ffreestanding ########## # Others # ########## # Remove warnings ... # -Wno-format-security -Wno-format-nonliteral  # C++ options # CXXFLAGS += -fvisibility=hidden -fno-strict-aliasing #################### # C specific flags # #################### # Warn if a function is declared or defined without specifying the argument types # Don't use GCC built-in functions # (C only) CFLAGS += -Wstrict-prototypes -fno-builtin ############################ # Assembler specific flags # ############################ ASFLAGS += $(CPPFLAGS) # For calls to u-boot functions ASFLAGS += -D__ASSEMBLY__ ################# # Objcopy flags # ################# # Fill gaps between sections with 0xff OBJCFLAGS += --gap-fill=0xff ######################################################################### TARGET = hello_world CRT = crt0.o stubs.o all:$(TARGET) clean:	rm -f *.o *.a *.bin *.su	rm -f $(TARGET) ######################################################################### $(TARGET): %: %.o $(CRT) $(LD) -g $(EX_LDFLAGS) -T asm.lds -o $@ $^ $(OBJCOPY) -O binary $@ $@.bin 2>/dev/null ######################################################################### 

[GitMensch]

It does an objcopy call after creating the binary - is there different output if you use the executable "${workspaceFolder}/x86/hello_world", directly?

[A2va]

Thanks, that worked by setting "${workspaceFolder}/x86/hello_world".
I still get two notification errors:

Failed to get Stack Trace: Selected thread is running. (from stack-info-depth --thread 1) Could not get threads: Cannot execute this command while the target is running. Use the "interrupt" command to stop the target and then try again. (from thread-info) 

But at least the debugging works.