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

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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: Mark Wielaard <mark@klomp.org>
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Hendrik Brueckner 2017-11-20 11:41:07 +01:00 committed by Martin Schwidefsky
parent a5f1005517
commit bc3703f21c
13 changed files with 43 additions and 0 deletions
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1
arch/s390/Makefile
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@ -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

25
arch/s390/include/asm/dwarf.h Normal file
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@ -0,0 +1,25 @@
/* 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 */

3
arch/s390/kernel/vdso32/Makefile
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@ -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

1
arch/s390/kernel/vdso32/clock_getres.S
View File

@ -9,6 +9,7 @@
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/dwarf.h>
.text
.align 4

1
arch/s390/kernel/vdso32/clock_gettime.S
View File

@ -9,6 +9,7 @@
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/dwarf.h>
.text
.align 4

1
arch/s390/kernel/vdso32/getcpu.S
View File

@ -8,6 +8,7 @@
*/
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/dwarf.h>
.text
.align 4

1
arch/s390/kernel/vdso32/gettimeofday.S
View File

@ -9,6 +9,7 @@
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/dwarf.h>
.text
.align 4

3
arch/s390/kernel/vdso64/Makefile
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@ -10,6 +10,9 @@ obj-vdso64 = gettimeofday.o clock_getres.o clock_gettime.o note.o getcpu.o
targets := $(obj-vdso64) vdso64.so vdso64.so.dbg
obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
KBUILD_AFLAGS += -DBUILD_VDSO
KBUILD_CFLAGS += -DBUILD_VDSO
KBUILD_AFLAGS_64 := $(filter-out -m64,$(KBUILD_AFLAGS))
KBUILD_AFLAGS_64 += -m64 -s

1
arch/s390/kernel/vdso64/clock_getres.S
View File

@ -9,6 +9,7 @@
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/dwarf.h>
.text
.align 4

1
arch/s390/kernel/vdso64/clock_gettime.S
View File

@ -9,6 +9,7 @@
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/dwarf.h>
.text
.align 4

1
arch/s390/kernel/vdso64/getcpu.S
View File

@ -8,6 +8,7 @@
*/
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/dwarf.h>
.text
.align 4

1
arch/s390/kernel/vdso64/gettimeofday.S
View File

@ -9,6 +9,7 @@
#include <asm/vdso.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/dwarf.h>
.text
.align 4

3
arch/s390/kernel/vmlinux.lds.S
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@ -141,4 +141,7 @@ SECTIONS
/* Sections to be discarded */
DISCARDS
/DISCARD/ : {
*(.eh_frame)
}
}