Messages in this thread Patch in this message | | | From | Dmitry Safonov <> | Subject | [PATCH 18/32] x86/vdso.lds: Align !timens (host's) vdso.so entries | Date | Wed, 6 Feb 2019 00:10:52 +0000 |
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As it has been discussed on timens RFC, adding a new conditional branch `if (inside_time_ns)` on VDSO for all processes is undesirable. It will add a penalty for everybody as branch predictor may mispredict the jump. Also there are instruction cache lines wasted on cmp/jmp.
Those effects of introducing time namespace are very much unwanted having in mind how much work have been spent on micro-optimisation vdso code.
Addressing those problems, there are two versions of VDSO's .so: for host tasks (without any penalty) and for processes inside of time namespace with clk_to_ns() that subtracts offsets from host's time.
Unfortunately, to allow changing VDSO VMA on a running process, the entry points to VDSO should have the same offsets (addresses). That's needed as i.e. application that calls setns() may have already resolved VDSO symbols in GOT/PLT.
Align VDSO entries for host with addresses generated from timens VDSO (which is bigger as it has code for adding offsets).
Signed-off-by: Dmitry Safonov <dima@arista.com> --- arch/x86/entry/vdso/vdso-layout.lds.S | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S index ba216527e59f..e529ee3ec9e8 100644 --- a/arch/x86/entry/vdso/vdso-layout.lds.S +++ b/arch/x86/entry/vdso/vdso-layout.lds.S @@ -70,7 +70,17 @@ SECTIONS * stuff that isn't used at runtime in between. */ - .text : { *(.text*) } :text =0x90909090, + .text : { +#if defined(CONFIG_TIME_NS) && !defined(UNALIGNED_ENTRIES) +#ifdef BUILD_VDSO32 +# include "vdso32.entries" +#endif +#ifdef BUILD_VDSO64 +# include "vdso64.entries" +#endif +#endif + *(.text*) + } :text =0x90909090, .altinstructions : { *(.altinstructions) } :text .altinstr_replacement : { *(.altinstr_replacement) } :text -- 2.20.1
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