Messages in this thread | | | From | Hui Zhu <> | Date | Mon, 29 Nov 2010 16:24:42 +0800 | Subject | Re: [PATCH] Built kernel without -O2 option |
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On Mon, Nov 29, 2010 at 16:16, Américo Wang <xiyou.wangcong@gmail.com> wrote: > On Mon, Nov 29, 2010 at 11:56:15AM +0800, Hui Zhu wrote: >>Hi, >> >>Now, there are a lot of ways to debug the Linux kernel with GDB, like >>qemu, kgtp or kgdb and so on. >>But the developer more like add a printk. It have a lot of reason, a big one is: >>(gdb) p ret >>$3 = <value optimized out> >>And the code execution order is not right. >> >>This is becuase the Kernel is bult with gcc -O2. Gcc will not >>generate enough debug message with file with -O2. >>So GDB cannot work very well with Linux kernel. >> >>So I make a patch that add a option in "Kernel hacking" called "Close >>GCC optimization". It will make kernel be built without -O2. >> >>I built and use it in i386 and x86_64. I will try to make it OK in other arch. >> > > The problem is that some functions _have to_ be inlined and gcc without -O2 > doesn't inline them. Have check all the cases? I doubt.
If they really need O2, I set them to O2. Actually, this is the main work, find out the file that need the O2. :)
For example: ifdef CONFIG_CC_CLOSE_OPTIMIZATION CFLAGS_fpu.o += -O2 CFLAGS_aesni-intel_glue.o += -O2 CFLAGS_ghash-clmulni-intel_glue.o += -O2 endif
And I will try to find more of these type files.
> > Also, what is size of vmlinux before applying your patch and after that? > Does it increase too much? >
Before the patch: ls -alh vmlinuz-2.6.37-rc3+ -rw-r--r-- 1 root root 4.1M 2010-11-25 12:02 vmlinuz-2.6.37-rc3+ ls -alh b26no/vmlinux -rwxr-xr-x 1 teawater teawater 135M 2010-11-25 13:31 b26no/vmlinux
After the patch: ls -alh vmlinuz-2.6.37-rc3debug+ -rw-r--r-- 1 root root 4.6M 2010-11-25 14:02 vmlinuz-2.6.37-rc3debug+ ls -alh b26/vmlinux -rwxr-xr-x 1 teawater teawater 140M 2010-11-25 11:14 b26/vmlinux
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