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Message-ID: <20111219182908.GA2027@linaro.org>
Date: Mon, 19 Dec 2011 18:29:08 +0000
From: Dave Martin <dave.martin@...aro.org>
To: Mircea Gherzan <mgherzan@...il.com>
Cc: linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] ARM: net: JIT compiler for packet filters
On Mon, Dec 19, 2011 at 06:18:39PM +0000, Dave Martin wrote:
> On Mon, Dec 19, 2011 at 06:45:13PM +0200, Mircea Gherzan wrote:
[...]
> > The JITed code calls back to the kernel for the load helpers. So setting
> > bit 0 is required.
>
> When you take the address of a link-time external function symbol,
> bit[0] in the address will automatically be set appropriately by the
> linker to indicate the target instruction set -- you already use BX/BLX
> to jump to such symbols, so you should switch correctly when calling
> _to_ the kernel.
>
> Returns should also work, except for old-style "mov pc,lr" returns made
> in Thumb code (from ARM code, this magically works for >= v7). Such returns
> only happen in hand-written assembler: for C code, the compiler always
> generates proper AEABI-compliant return sequences.
>
> So, for calling load_func[], jit_get_skb_b etc. (which are C functions),
> there should be no problem.
>
> I think the only code which you call from the JIT output but which does
> not return compliantly is __aeabi_uidiv() in arch/arm/lib/lib1funcs.S.
>
>
> I have a quick hacked-up patch (below) which attempts to fix this;
> I'd be interested if this works for you -- but finalising your ARM-only
> version of the patch should still be the priority.
>
> If this fix does work, I'll turn it into a proper patch, as we can maybe
> use it more widely.
Oops, I forgot to paste in my patch ... here it is.
Cheers
---Dave
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index b6e65de..013bfaf 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -313,4 +313,39 @@
.size \name , . - \name
.endm
+/*
+ * Helper macro to abstract a function return, where the return address is
+ * held in a register:
+ */
+.macro __def_bret cc
+ .macro bret\cc Rm:req
+#if __LINUX_ARM_ARCH__ < 7
+ mov\cc pc, \Rm
+#else
+ bx\cc \Rm
+#endif
+
+ .endm
+.endm
+
+__def_bret
+__def_bret eq
+__def_bret ne
+__def_bret hs
+__def_bret cs
+__def_bret lo
+__def_bret cc
+__def_bret vs
+__def_bret vc
+__def_bret mi
+__def_bret pl
+__def_bret hi
+__def_bret ls
+__def_bret ge
+__def_bret lt
+__def_bret gt
+__def_bret le
+
+.purgem __def_bret
+
#endif /* __ASM_ASSEMBLER_H__ */
diff --git a/arch/arm/lib/lib1funcs.S b/arch/arm/lib/lib1funcs.S
index c562f64..c3a4dbf 100644
--- a/arch/arm/lib/lib1funcs.S
+++ b/arch/arm/lib/lib1funcs.S
@@ -210,7 +210,7 @@ ENTRY(__aeabi_uidiv)
UNWIND(.fnstart)
subs r2, r1, #1
- moveq pc, lr
+ breteq lr
bcc Ldiv0
cmp r0, r1
bls 11f
@@ -220,16 +220,16 @@ UNWIND(.fnstart)
ARM_DIV_BODY r0, r1, r2, r3
mov r0, r2
- mov pc, lr
+ bret lr
11: moveq r0, #1
movne r0, #0
- mov pc, lr
+ bret lr
12: ARM_DIV2_ORDER r1, r2
mov r0, r0, lsr r2
- mov pc, lr
+ bret lr
UNWIND(.fnend)
ENDPROC(__udivsi3)
@@ -244,11 +244,11 @@ UNWIND(.fnstart)
moveq r0, #0
tsthi r1, r2 @ see if divisor is power of 2
andeq r0, r0, r2
- movls pc, lr
+ bretls lr
ARM_MOD_BODY r0, r1, r2, r3
- mov pc, lr
+ bret lr
UNWIND(.fnend)
ENDPROC(__umodsi3)
@@ -274,23 +274,23 @@ UNWIND(.fnstart)
cmp ip, #0
rsbmi r0, r0, #0
- mov pc, lr
+ bret lr
10: teq ip, r0 @ same sign ?
rsbmi r0, r0, #0
- mov pc, lr
+ bret lr
11: movlo r0, #0
moveq r0, ip, asr #31
orreq r0, r0, #1
- mov pc, lr
+ bret lr
12: ARM_DIV2_ORDER r1, r2
cmp ip, #0
mov r0, r3, lsr r2
rsbmi r0, r0, #0
- mov pc, lr
+ bret lr
UNWIND(.fnend)
ENDPROC(__divsi3)
@@ -315,7 +315,7 @@ UNWIND(.fnstart)
10: cmp ip, #0
rsbmi r0, r0, #0
- mov pc, lr
+ bret lr
UNWIND(.fnend)
ENDPROC(__modsi3)
@@ -331,7 +331,7 @@ UNWIND(.save {r0, r1, ip, lr} )
ldmfd sp!, {r1, r2, ip, lr}
mul r3, r0, r2
sub r1, r1, r3
- mov pc, lr
+ bret lr
UNWIND(.fnend)
ENDPROC(__aeabi_uidivmod)
@@ -344,7 +344,7 @@ UNWIND(.save {r0, r1, ip, lr} )
ldmfd sp!, {r1, r2, ip, lr}
mul r3, r0, r2
sub r1, r1, r3
- mov pc, lr
+ bret lr
UNWIND(.fnend)
ENDPROC(__aeabi_idivmod)
--
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