linux-kernel - Re: [PATCH/RFC] powerpc: avoid generating .eh

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Message-ID: <20090224084034.GA11847@uranus.ravnborg.org>
Date:	Tue, 24 Feb 2009 09:40:34 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Kyle McMartin <kyle@...radead.org>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	kyle@...hat.com, roland@...hat.com, aoliva@...hat.com
Subject: Re: [PATCH/RFC] powerpc: avoid generating .eh_frame sections with gcc-4.4

On Tue, Feb 24, 2009 at 01:51:12AM -0500, Kyle McMartin wrote:
> From: Kyle McMartin <kyle@...hat.com>
> 
> On ppc64 (at least) gcc-4.4 is defaulting to generating .eh_frame
> sections, which are, for the kernel, fairly pointless. Additionally, on
> ppc64 this generates a relocation format which the kernel module loader
> does not currently support (R_PPC64_REL32.)
> 
> Alexandre Oliva verifies that -fno-dwarf2-cfi-asm prevents this
> .eh_frame section from being generated.
> 
> These seem to be used for unwinding, but it doesn't look like we
> currently use them anywhere. (In fact, we explicitly dump them in the
> x86_64 linker script.)

A grep for "eh_frame" shows too many hits in the kernel to convince
me this is true.

arch/m32r/kernel/vmlinux.lds.S:     from .altinstructions and .eh_frame */
arch/mn10300/kernel/vmlinux.lds.S:     from .altinstructions and .eh_frame */
arch/parisc/kernel/vmlinux.lds.S:        *  from .altinstructions and .eh_frame
arch/powerpc/kernel/vdso32/sigtramp.S:  .section .eh_frame,"a",@progbits
arch/powerpc/kernel/vdso32/vdso32.lds.S:        .eh_frame_hdr   : { *(.eh_frame_hdr) }   :text    :eh_frame_hdr
arch/powerpc/kernel/vdso32/vdso32.lds.S:        .eh_frame       : { KEEP (*(.eh_frame)) }:text
arch/powerpc/kernel/vdso32/vdso32.lds.S:        eh_frame_hdr    PT_GNU_EH_FRAME;
arch/powerpc/kernel/vdso64/sigtramp.S:  .section .eh_frame,"a",@progbits
arch/powerpc/kernel/vdso64/vdso64.lds.S:        .eh_frame_hdr   : { *(.eh_frame_hdr) }   :text    :eh_frame_hdr
arch/powerpc/kernel/vdso64/vdso64.lds.S:        .eh_frame       : { KEEP (*(.eh_frame)) }:text
arch/powerpc/kernel/vdso64/vdso64.lds.S:        eh_frame_hdr    PT_GNU_EH_FRAME;
arch/s390/kernel/vdso32/vdso32.lds.S:   .eh_frame_hdr   : { *(.eh_frame_hdr) }          :text     :eh_frame_hdr
arch/s390/kernel/vdso32/vdso32.lds.S:   .eh_frame       : { KEEP (*(.eh_frame)) }       :text
arch/s390/kernel/vdso32/vdso32.lds.S:   eh_frame_hdr    PT_GNU_EH_FRAME;
arch/s390/kernel/vdso64/vdso64.lds.S:   .eh_frame_hdr   : { *(.eh_frame_hdr) }          :text     :eh_frame_hdr
arch/s390/kernel/vdso64/vdso64.lds.S:   .eh_frame       : { KEEP (*(.eh_frame)) }       :text
arch/s390/kernel/vdso64/vdso64.lds.S:   eh_frame_hdr    PT_GNU_EH_FRAME;
arch/sh/kernel/vsyscall/vsyscall-sigreturn.S:   .section .eh_frame,"a",@progbits
arch/sh/kernel/vsyscall/vsyscall-trapa.S:        * fill out .eh_frame -- PFM. */
arch/sh/kernel/vsyscall/vsyscall-trapa.S:       .section .eh_frame,"a",@progbits
arch/sh/kernel/vsyscall/vsyscall.lds.S: .eh_frame_hdr   : { *(.eh_frame_hdr ) }         :text     :eh_frame_hdr
arch/sh/kernel/vsyscall/vsyscall.lds.S: .eh_frame       : {
arch/sh/kernel/vsyscall/vsyscall.lds.S:         KEEP (*(.eh_frame))
arch/sh/kernel/vsyscall/vsyscall.lds.S: eh_frame_hdr    PT_GNU_EH_FRAME;
arch/um/include/asm/common.lds.S:     from .altinstructions and .eh_frame */
arch/um/kernel/dyn.lds.S:  .eh_frame       : { KEEP (*(.eh_frame)) }
arch/x86/kernel/vmlinux_32.lds.S:     from .altinstructions and .eh_frame */
arch/x86/kernel/vmlinux_64.lds.S:     from .altinstructions and .eh_frame */
arch/x86/kernel/vmlinux_64.lds.S:       *(.eh_frame)
arch/x86/vdso/vdso-layout.lds.S:        .eh_frame_hdr   : { *(.eh_frame_hdr) }          :text     :eh_frame_hdr
arch/x86/vdso/vdso-layout.lds.S:        .eh_frame       : { KEEP (*(.eh_frame)) }       :text
arch/x86/vdso/vdso-layout.lds.S:        eh_frame_hdr    PT_GNU_EH_FRAME;
arch/x86/vdso/vdso32/int80.S:   .section .eh_frame,"a",@progbits
arch/x86/vdso/vdso32/int80.S:VDSO32_vsyscall_eh_frame_size = 0x40
arch/x86/vdso/vdso32/int80.S:   .space VDSO32_vsyscall_eh_frame_size-(.LENDFDEDLSI-.LSTARTFRAMEDLSI), 0
arch/x86/vdso/vdso32/sigreturn.S:       .section .eh_frame,"a",@progbits
arch/x86/vdso/vdso32/syscall.S: .section .eh_frame,"a",@progbits
arch/x86/vdso/vdso32/syscall.S:VDSO32_vsyscall_eh_frame_size = 0x40
arch/x86/vdso/vdso32/syscall.S: .space VDSO32_vsyscall_eh_frame_size-(.LENDFDE1-.LSTARTFRAME), 0
arch/x86/vdso/vdso32/sysenter.S:        .section .eh_frame,"a",@progbits
arch/x86/vdso/vdso32/sysenter.S:         * Emit a symbol with the size of this .eh_frame data,
arch/x86/vdso/vdso32/sysenter.S:VDSO32_vsyscall_eh_frame_size = (.LENDFDEDLSI-.LSTARTFRAMEDLSI)

x86 has a specific ".section .eh_frame,"a",@progbits" in vdso32/int80.S as one example.

Have you analyzed all these hits?

	Sam
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