Commit bc3703f2 authored by Hendrik Brueckner's avatar Hendrik Brueckner Committed by Martin Schwidefsky
Browse files

s390/kernel: emit CFI data in .debug_frame and discard .eh_frame sections 

Using perf probe and libdw on kernel modules failed to find CFI
data for symbols.  The CFI data is stored in the .eh_frame section.
The elfutils libdw is not able to extract the CFI data correctly,
because the .eh_frame section requires "non-simple" relocations
for kernel modules.

The suggestion is to avoid these "non-simple" relocations by emitting
the CFI data in the .debug_frame section.  Let gcc emit respective
directives by specifying the -fno-asynchronous-unwind-tables option.

Using the .debug_frame section for CFI data, the .eh_frame section
becomes unused and, thus, discard it for kernel and modules builds

The vDSO requires the .eh_frame section and, hence, emit the CFI data
in both, the .eh_frame and .debug_frame sections.

See also discussion on elfutils/libdw bugzilla:
https://sourceware.org/bugzilla/show_bug.cgi?id=22452



Suggested-by: default avatarMark Wielaard <mark@klomp.org>
Signed-off-by: default avatarHendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent a5f10055

arch/s390/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -90,6 +90,7 @@ endif 


KBUILD_CFLAGS	+= -mbackchain -msoft-float $(cflags-y)

KBUILD_CFLAGS	+= -pipe -fno-strength-reduce -Wno-sign-compare

KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables

KBUILD_AFLAGS	+= $(aflags-y)



OBJCOPYFLAGS	:= -O binary

arch/s390/include/asm/dwarf.h

0 → 100644
+25 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _ASM_S390_DWARF_H

#define _ASM_S390_DWARF_H



#ifdef __ASSEMBLY__



#ifndef BUILD_VDSO

	/*

	 * Emit CFI data in .debug_frame sections and not in .eh_frame

	 * sections.  The .eh_frame CFI is used for runtime unwind

	 * information that is not being used.  Hence, vmlinux.lds.S

	 * can discard the .eh_frame sections.

	 */

	.cfi_sections .debug_frame

#else

	/*

	 * For vDSO, emit CFI data in both, .eh_frame and .debug_frame

	 * sections.

	 */

	.cfi_sections .eh_frame, .debug_frame

#endif



#endif	/* __ASSEMBLY__ */



#endif	/* _ASM_S390_DWARF_H */

arch/s390/kernel/vdso32/Makefile

+3 −0
Original line number Diff line number Diff line
@@ -10,6 +10,9 @@ obj-vdso32 = gettimeofday.o clock_getres.o clock_gettime.o note.o getcpu.o 
targets := $(obj-vdso32) vdso32.so vdso32.so.dbg

obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))



KBUILD_AFLAGS += -DBUILD_VDSO

KBUILD_CFLAGS += -DBUILD_VDSO



KBUILD_AFLAGS_31 := $(filter-out -m64,$(KBUILD_AFLAGS))

KBUILD_AFLAGS_31 += -m31 -s

arch/s390/kernel/vdso32/clock_getres.S

+1 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
#include <asm/vdso.h>

#include <asm/asm-offsets.h>

#include <asm/unistd.h>

#include <asm/dwarf.h>



	.text

	.align 4

arch/s390/kernel/vdso32/clock_gettime.S

+1 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
#include <asm/vdso.h>

#include <asm/asm-offsets.h>

#include <asm/unistd.h>

#include <asm/dwarf.h>



	.text

	.align 4

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