Re: [PATCH] x86: vdso: Pass --eh-frame-hdr to ld

From: Laura Abbott
Date: Fri Dec 14 2018 - 17:32:11 EST

On 12/14/18 2:27 PM, Alistair Strachan wrote:
Commit 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
accidentally broke unwinding from userspace, because ld would strip the
.eh_frame sections when linking.

Originally, the compiler would implicitly add --eh-frame-hdr when
invoking the linker, but when this Makefile was converted from invoking
ld via the compiler, to invoking it directly (like vmlinux does),
the flag was missed. (The EH_FRAME section is important for the VDSO
shared libraries, but not for vmlinux.)

Fix the problem by explicitly specifying --eh-frame-hdr, which restores
parity with the old method.

Reported-by: Laura Abbott <labbott@xxxxxxxxxx>

You should probably use the bugzilla reporters instead
of me given I just did the boring part of sending an e-mail.
Instead you can use:

Tested-by: Laura Abbott <labbott@xxxxxxxxxx>

Fixes: 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: X86 ML <x86@xxxxxxxxxx>
Cc: Florian Weimer <fweimer@xxxxxxxxxx>,
Cc: Carlos O'Donell <carlos@xxxxxxxxxx>,
Cc: "H. J. Lu" <>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
Signed-off-by: Alistair Strachan <astrachan@xxxxxxxxxx>
arch/x86/entry/vdso/Makefile | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 141d415a8c80..c3d7ccd25381 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -171,7 +171,8 @@ quiet_cmd_vdso = VDSO $@
sh $(srctree)/$(src)/ '$(NM)' '$@'
VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
- $(call ld-option, --build-id) -Bsymbolic
+ $(call ld-option, --build-id) $(call ld-option, --eh-frame-hdr) \
+ -Bsymbolic