Messages in this thread | | | Date | Fri, 25 Nov 2022 12:27:14 +0000 | From | Szabolcs Nagy <> | Subject | Re: [PATCH] arm64: vdso: Include .eh_frame in debug ELF |
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The 11/25/2022 11:37, Vincent Whitchurch wrote: > We currently strip out .eh_frame to work around crashes in libgcc when > it tries to unwind out of signal handlers, see commit 87676cfca141 > ("arm64: vdso: Disable dwarf unwinding through the sigreturn > trampoline"). > > The .eh_frame does however have correct unwind information for the > functions implemented in C in vgettimeofday.c, but currently this > information is not available even for offline unwinding using the > vdso.so.dbg. As a result of this, perf built with libdw is unable to > unwind the stack when the PC is inside one of these functions. > > To fix this, strip the .eh_frame section only from the vdso.so and not > from the vdso.so.dbg. This can be used by offline unwinders with access > to the debug symbols, and will not affect libgcc since the section will > still not be present in the normal vDSO.
adding eh_frame to vdso.so.dbg makes sense.
but if libdw correctly unwinds across a signal handler then libgcc should be able to do so too.
so maybe eh_frame should be added back to vdso.so just without frame info for __kernel_rt_sigreturn+NOP to ensure unwinders use heuristics for sigreturn. (i dont know if this was considered back when eh_frame was dropped from the vdso)
> > Cc: Tamas Zsoldos <tamas.zsoldos@arm.com> > Cc: Szabolcs Nagy <szabolcs.nagy@arm.com> > Cc: Daniel Kiss <daniel.kiss@arm.com> > Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> > Cc: Ard Biesheuvel <ardb@kernel.org> > Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> > --- > arch/arm64/kernel/vdso/Makefile | 2 +- > arch/arm64/kernel/vdso/vdso.lds.S | 3 ++- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile > index 619e2dc7ee14..91aac17e11bc 100644 > --- a/arch/arm64/kernel/vdso/Makefile > +++ b/arch/arm64/kernel/vdso/Makefile > @@ -65,7 +65,7 @@ $(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE > $(call if_changed,vdsold_and_vdso_check) > > # Strip rule for the .so file > -$(obj)/%.so: OBJCOPYFLAGS := -S > +$(obj)/%.so: OBJCOPYFLAGS := -S --remove-section=.eh_frame --remove-section=.eh_frame_hdr > $(obj)/%.so: $(obj)/%.so.dbg FORCE > $(call if_changed,objcopy) > > diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S > index 6028f1fe2d1c..66abf70efc58 100644 > --- a/arch/arm64/kernel/vdso/vdso.lds.S > +++ b/arch/arm64/kernel/vdso/vdso.lds.S > @@ -31,6 +31,8 @@ SECTIONS > .gnu.version : { *(.gnu.version) } > .gnu.version_d : { *(.gnu.version_d) } > .gnu.version_r : { *(.gnu.version_r) } > + .eh_frame : { *(.eh_frame) } > + .eh_frame_hdr : { *(.eh_frame_hdr) } > > /* > * Discard .note.gnu.property sections which are unused and have > @@ -78,7 +80,6 @@ SECTIONS > /DISCARD/ : { > *(.data .data.* .gnu.linkonce.d.* .sdata*) > *(.bss .sbss .dynbss .dynsbss) > - *(.eh_frame .eh_frame_hdr) > } > } > > -- > 2.34.1 >
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