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Date: Mon, 29 Nov 2010 16:57:58 +0800 From: Hui Zhu <teawater@...il.com> To: Steven <mqyoung@...il.com> Cc: hellogcc@...elists.org, Américo Wang <xiyou.wangcong@...il.com>, linux-kernel@...r.kernel.org, gdb@...rceware.org Subject: Re: [hellogcc] Re: [PATCH] Built kernel without -O2 option On Mon, Nov 29, 2010 at 16:55, Steven <mqyoung@...il.com> wrote: > I replace -O2 with -O0 in Makefile of kernel source code root directory? > I just do it and my gdb works well with this method. > > You mean it is not enough? > > Steven Yes. > > On Mon, 2010-11-29 at 16:47 +0800, Hui Zhu wrote: >> In this way, you will got a lot of error. >> >> Hui >> >> On Mon, Nov 29, 2010 at 16:41, 乔崇 <qiaochong@...ngson.cn> wrote: >> > does not need change kernel,just write a shell mycc as bellow: >> > >> > #!/bin/sh >> > gcc "$@" -O0 >> > >> > then >> > >> > make CC=./mycc vmlinux >> > >> > Hui Zhu said >> > >> > On Mon, Nov 29, 2010 at 16:16, Américo Wang <xiyou.wangcong@...il.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 >> > >> > Thanks, >> > Hui >> > >> > >> > >> > >> > -- >> > >> > 乔崇 qiaochong@...ngson.cn >> > >> > 2010年 11月 29日 星期一 16:35:38 CST > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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