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Re: [PATCH] Built kernel without -O2 option
- From: AmÃrico Wang <xiyou dot wangcong at gmail dot com>
- To: Hui Zhu <teawater at gmail dot com>
- Cc: linux-kernel at vger dot kernel dot org, gdb at sourceware dot org, hellogcc at freelists dot org
- Date: Mon, 29 Nov 2010 16:16:19 +0800
- Subject: Re: [PATCH] Built kernel without -O2 option
- References: <AANLkTimewZ4QhxzL2vOYYV85pegy8Fu6Rb4XUAPqGUXS@mail.gmail.com>
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.
Also, what is size of vmlinux before applying your patch and after that?
Does it increase too much?