Re: [PATCH v8 2/7] arm64: Add more test functions to insn.c

From: David Long
Date: Thu Aug 13 2015 - 00:23:13 EST

On 08/11/15 14:00, Will Deacon wrote:
On Tue, Aug 11, 2015 at 01:52:39AM +0100, David Long wrote:
From: "David A. Long" <dave.long@xxxxxxxxxx>

Certain instructions are hard to execute correctly out-of-line (as in
kprobes). Test functions are added to insn.[hc] to identify these. The
instructions include any that use PC-relative addressing, change the PC,
or change interrupt masking. For efficiency and simplicity test
functions are also added for small collections of related instructions.

Signed-off-by: David A. Long <dave.long@xxxxxxxxxx>
arch/arm64/include/asm/insn.h | 18 ++++++++++++++++++
arch/arm64/kernel/insn.c | 28 ++++++++++++++++++++++++++++
2 files changed, 46 insertions(+)

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index 30e50eb..66bfb21 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -223,8 +223,13 @@ static __always_inline bool aarch64_insn_is_##abbr(u32 code) \
static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
{ return (val); }

+__AARCH64_INSN_FUNCS(adr_adrp, 0x1F000000, 0x10000000)
+__AARCH64_INSN_FUNCS(prfm_lit, 0xFF000000, 0xD8000000)
__AARCH64_INSN_FUNCS(str_reg, 0x3FE0EC00, 0x38206800)
__AARCH64_INSN_FUNCS(ldr_reg, 0x3FE0EC00, 0x38606800)
+__AARCH64_INSN_FUNCS(ldr_lit, 0xBF000000, 0x18000000)
+__AARCH64_INSN_FUNCS(ldrsw_lit, 0xFF000000, 0x98000000)
+__AARCH64_INSN_FUNCS(exclusive, 0x3F000000, 0x08000000)

Hmm, so this class also pulls in load-acquire and store-release, which
we *should* be able to single-step, no? Maybe it's worth splitting this
category up (or at least changing aarch64_insn_is_exclusive to be more

I was not confident that this was the case. After reading the relevant parts of the v8 ARM yet again I think I see your point.

__AARCH64_INSN_FUNCS(stp_post, 0x7FC00000, 0x28800000)
__AARCH64_INSN_FUNCS(ldp_post, 0x7FC00000, 0x28C00000)
__AARCH64_INSN_FUNCS(stp_pre, 0x7FC00000, 0x29800000)
@@ -264,19 +269,29 @@ __AARCH64_INSN_FUNCS(ands, 0x7F200000, 0x6A000000)
__AARCH64_INSN_FUNCS(bics, 0x7F200000, 0x6A200000)
__AARCH64_INSN_FUNCS(b, 0xFC000000, 0x14000000)
__AARCH64_INSN_FUNCS(bl, 0xFC000000, 0x94000000)
+__AARCH64_INSN_FUNCS(b_bl, 0x7C000000, 0x14000000)

Why do we need this when we already have checks for b and bl?

I was trying to avoid doing multiple checks for different variants of similar instructions.

+__AARCH64_INSN_FUNCS(cb, 0x7E000000, 0x34000000)

Likewise for cbz and cbnz...

__AARCH64_INSN_FUNCS(cbz, 0x7F000000, 0x34000000)
__AARCH64_INSN_FUNCS(cbnz, 0x7F000000, 0x35000000)
+__AARCH64_INSN_FUNCS(tb, 0x7E000000, 0x36000000)

... there's a pattern here!


__AARCH64_INSN_FUNCS(tbz, 0x7F000000, 0x36000000)
__AARCH64_INSN_FUNCS(tbnz, 0x7F000000, 0x37000000)
+__AARCH64_INSN_FUNCS(b_bl_cb_tb, 0x5C000000, 0x14000000)

I must be missing something :)


__AARCH64_INSN_FUNCS(bcond, 0xFF000010, 0x54000000)
__AARCH64_INSN_FUNCS(svc, 0xFFE0001F, 0xD4000001)
__AARCH64_INSN_FUNCS(hvc, 0xFFE0001F, 0xD4000002)
__AARCH64_INSN_FUNCS(smc, 0xFFE0001F, 0xD4000003)
__AARCH64_INSN_FUNCS(brk, 0xFFE0001F, 0xD4200000)
+__AARCH64_INSN_FUNCS(exception, 0xFF000000, 0xD4000000)
__AARCH64_INSN_FUNCS(hint, 0xFFFFF01F, 0xD503201F)
__AARCH64_INSN_FUNCS(br, 0xFFFFFC1F, 0xD61F0000)
__AARCH64_INSN_FUNCS(blr, 0xFFFFFC1F, 0xD63F0000)
+__AARCH64_INSN_FUNCS(br_blr, 0xFFDFFC1F, 0xD61F0000)
__AARCH64_INSN_FUNCS(ret, 0xFFFFFC1F, 0xD65F0000)
+__AARCH64_INSN_FUNCS(msr_imm, 0xFFF8F01F, 0xD500401F)
+__AARCH64_INSN_FUNCS(msr_reg, 0xFFF00000, 0xD5100000)
+__AARCH64_INSN_FUNCS(set_clr_daif, 0xFFFFF0DF, 0xD50340DF)
+__AARCH64_INSN_FUNCS(rd_wr_daif, 0xFFDFFFE0, 0xD51B4220)

I think I'd rather have separate decoders to decode the register field
of an mrs/msr instruction than overload each encoding here.

Anyway, on the whole this looks pretty good, I'd just prefer not to build
compound instruction checks at the encoding level (even though it looks
like you did a good job on the values).

OK, easy enough to just add to the if statements where these are getting used. May be getting a little bloated looking there though.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at