Messages in this thread | | | Date | Wed, 29 Jun 2005 17:17:02 +0530 | From | Vivek Goyal <> | Subject | Re: [Fastboot] Re: [-mm patch] i386: enable REGPARM by default |
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> > In this case I am building linux kernel with debug info (-g) and -mregparm > > is not specified. So parameters should be passed on stack. Following > > is the effective command line to build kernel/sysfs.c. I am not sure if > > any of the below mentioned options are going to affect the gdb results. > > > > gcc -m32 -Wp,-MD,kernel/.ksysfs.o.d -nostdinc -isystem > > /usr/lib/gcc/i386-redhat-linux/3.4.3/include -D__KERNEL__ -Iinclude > > -Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing > > -fno-common -ffreestanding -O2 -fomit-frame-pointer -g -pipe > > -msoft-float -mpreferred-stack-boundary=2 -fno-unit-at-a-time > > -march=i686 -mtune=pentium4 -Iinclude/asm-i386/mach-default > > -Wdeclaration-after-statement -DKBUILD_BASENAME=ksysfs > > -DKBUILD_MODNAME=ksysfs -c -o kernel/ksysfs.o kernel/ksysfs.c > > -O2 will have some effect. The compiler might optimize away variables > (including function arguments) and doesn't always record that fact in > the debug information. > > But the real killer here is probably -fomit-frame-pointer. Last time I > looked GCC didn't generate the correct debug information in that case. > I didn't really look into this, but it seemed as if GCC blindly produces > location descriptions relative to the frame pointer even though there no > longer is a frame pointer. GCC 4.0 or 4.1 might have this fixed. > > > > >> Repeating what Daniel said before, by using "regparm", function > >> arguments are now passed in registers instead of on the stack. It's > >> extremely unlikely that these function arguments will stay in those > >> registers for ever, especially since you've only got a handfull of > >> them on the i386. > > > > Sorry for the confusion. In the last mail all the results were reported > > with REGPARM disabled. I wanted to make sure that first normal case works > > fine and then discuss the REGPARM case later. > > If you're prepared to do some more tests, you might want to check out > what happens if you leave out -O2 and -fomit-frame-pointer, and then add > back only -O2
I built another kernel with -fno-omit-frame-pointer and output seems to have worsen a lot now. I am not able to build a kernel without -02. There seems to be some dependencies which I am sorting out.
With frame pointer support, following is the command line.
gcc -m32 -Wp,-MD,kernel/.ksysfs.o.d -nostdinc -isystem /usr/lib/gcc/i386-redhat-linux/3.4.3/include -D__KERNEL__ -Iinclude -Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -ffreestanding -O2 -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -pipe -msoft-float -mpreferred-stack-boundary=2 -fno-unit-at-a-time -march=i686 -mtune=pentium4 -Iinclude/asm-i386/mach-default -Wdeclaration-after-statement -DKBUILD_BASENAME=ksysfs -DKBUILD_MODNAME=ksysfs -c -o kernel/ksysfs.o kernel/ksysfs.c
And the gdb trace has worsened. Trace is not even showing all the calls as it was showing when kernel was built with -fomit-frame-pointer.
#0 crash_get_current_regs (regs=0xec3b5e34) at arch/i386/kernel/crash.c:103 #1 0xc0114077 in crash_save_self (saved_regs=0xec3b5e34) at arch/i386/kernel/crash.c:134 #2 0xec3b5f04 in ?? () #3 0x00000014 in ?? () #4 0xec3b5e98 in ?? () #5 0xc013d7e6 in crash_kexec (regs=0x2) at kernel/kexec.c:1059 #6 0xecb29c80 in ?? () #7 0xecb29c80 in ?? () #8 0x00000000 in ?? ()
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