CODEWITHSUNDEEP
c++gccgdbkernelcross-compiling
AlphaRL
AlphaRL

Reputation: 1629

Why can't gdb show debug info?

Here is my g++:

$ /usr/local/gcc-4.8.1-for-linux32/bin/i586-pc-linux-g++ -v
Using built-in specs.
COLLECT_GCC=/usr/local/gcc-4.8.1-for-linux32/bin/i586-pc-linux-g++
COLLECT_LTO_WRAPPER=/usr/local/gcc-4.8.1-for-linux32/libexec/gcc/i586-pc-linux/4.8.1/lto-wrapper
Target: i586-pc-linux
Configured with: ../gcc-4.8.1/configure --target=i586-pc-linux --build=i686-apple-darwin11 --prefix=/usr/local/gcc-4.8.1-for-linux32 --disable-multilib --enable-languages=c,c++ --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --disable-bootstrap
Thread model: posix
gcc version 4.8.1 (GCC)

gdb:

$ i386-linux-gdb -v
GNU gdb (GDB) 7.7.1
This GDB was configured as "--host=x86_64-apple-darwin15.5.0 --target=i386-linux".

CXX_FLAGS:

-ffreestanding -O0 -Wall -Wextra -fno-exceptions -fno-rtti -ggdb -nostdlib -std=c++11 -m32

generate kernel.bin:

/usr/local/gcc-4.8.1-for-linux32/bin/i586-pc-linux-g++ -I. -Iinclude -Ikernel -ffreestanding -O0 -Wall -Wextra -fno-exceptions -fno-rtti -ggdb -nostdlib -std=c++11 -m32 -e main -Ttext 0x100000 -o generated/kernel.bin generated/kernel/init/kernelMain.o generated/kernel/memoryManage/memoryManage.o
/usr/local/gcc-4.8.1-for-linux32/bin/i586-pc-linux-objdump -S -D generated/kernel.bin > generated/kernel.dump

I use qemu-i386 to load my toy OS, then my bootloader will parse kernel.bin, puts segments into memory. Then I start gdb in my host OS (OS X 10.11), execute:

file ./generated/kernel.bin
target remote localhost:1234
b initMemory
c

I can successfully stop at function initMemory which is in memoryManage.o.

8: x/i 0x100000 + $eip
   0x100010 <initMemory()>: push   %ebp

However when I execute n or s or p it doesn't work. I can only use si ni

(gdb) n
Cannot find bounds of current function
(gdb) s
Cannot find bounds of current function
(gdb) p memoryInfoAddr
No symbol "memoryInfoAddr" in current context.

How can I fix this problem? Is it caused by mismatch of i586 g++ and i386 gdb, or mismatch of gcc 4.8.1 and gdb 7.7.1?

Upvotes: 1

Views: 490

Answers (1)

AlphaRL
AlphaRL

Reputation: 1629

Finally I find out the problem. gdb use %eip to find instructions, however in my kernel it should use %cs:%eip. After setting %cs to 0, gdb works as expected.

Upvotes: 1

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