LoongArch: Relay BCE exceptions to userland as SIGSEGV with si_code=SEGV_BNDERR

SEGV_BNDERR was introduced initially for supporting the Intel MPX, but
fell into disuse after the MPX support was removed. The LoongArch
bounds-checking instructions behave very differently than MPX, but
overall the interface is still kind of suitable for conveying the
information to userland when bounds-checking assertions trigger, so we
wouldn't have to invent more UAPI. Specifically, when the BCE triggers,
a SEGV_BNDERR is sent to userland, with si_addr set to the out-of-bounds
address or value (in asrt{gt,le}'s case), and one of si_lower or
si_upper set to the configured bound depending on the faulting
instruction. The other bound is set to either 0 or ULONG_MAX to resemble
a range with both lower and upper bounds.

Note that it is possible to have si_addr == si_lower in case of a
failing asrtgt or {ld,st}gt, because those instructions test for strict
greater-than relationship. This should not pose a problem for userland,
though, because the faulting PC is available for the application to
associate back to the exact instruction for figuring out the
expectation.

Example exception context generated by a faulting `asrtgt.d t0, t1`
(assert t0 > t1 or BCE) with t0=100 and t1=200:

> pc 00005555558206a4 ra 00007ffff2d854fc tp 00007ffff2f2f180 sp 00007ffffbf9fb80
> a0 0000000000000002 a1 00007ffffbf9fce8 a2 00007ffffbf9fd00 a3 00007ffff2ed4558
> a4 0000000000000000 a5 00007ffff2f044c8 a6 00007ffffbf9fce0 a7 fffffffffffff000
> t0 0000000000000064 t1 00000000000000c8 t2 00007ffffbfa2d5e t3 00007ffff2f12aa0
> t4 00007ffff2ed6158 t5 00007ffff2ed6158 t6 000000000000002e t7 0000000003d8f538
> t8 0000000000000005 u0 0000000000000000 s9 0000000000000000 s0 00007ffffbf9fce8
> s1 0000000000000002 s2 0000000000000000 s3 00007ffff2f2c038 s4 0000555555820610
> s5 00007ffff2ed5000 s6 0000555555827e38 s7 00007ffffbf9fd00 s8 0000555555827e38
>    ra: 00007ffff2d854fc
>   ERA: 00005555558206a4
>  CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
>  PRMD: 00000007 (PPLV3 +PIE -PWE)
>  EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
>  ECFG: 0007181c (LIE=2-4,11-12 VS=7)
> ESTAT: 000a0000 [BCE] (IS= ECode=10 EsubCode=0)
>  PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)

Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

1 files changed, 26 insertions, 0 deletions

diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index a04fe755d719..b09887ffcd15 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -121,6 +121,8 @@ enum reg2bstrd_op {
 };
 
 enum reg3_op {
+	asrtle_op	= 0x02,
+	asrtgt_op	= 0x03,
 	addw_op		= 0x20,
 	addd_op		= 0x21,
 	subw_op		= 0x22,
@@ -176,6 +178,30 @@ enum reg3_op {
 	amord_op	= 0x70c7,
 	amxorw_op	= 0x70c8,
 	amxord_op	= 0x70c9,
+	fldgts_op	= 0x70e8,
+	fldgtd_op	= 0x70e9,
+	fldles_op	= 0x70ea,
+	fldled_op	= 0x70eb,
+	fstgts_op	= 0x70ec,
+	fstgtd_op	= 0x70ed,
+	fstles_op	= 0x70ee,
+	fstled_op	= 0x70ef,
+	ldgtb_op	= 0x70f0,
+	ldgth_op	= 0x70f1,
+	ldgtw_op	= 0x70f2,
+	ldgtd_op	= 0x70f3,
+	ldleb_op	= 0x70f4,
+	ldleh_op	= 0x70f5,
+	ldlew_op	= 0x70f6,
+	ldled_op	= 0x70f7,
+	stgtb_op	= 0x70f8,
+	stgth_op	= 0x70f9,
+	stgtw_op	= 0x70fa,
+	stgtd_op	= 0x70fb,
+	stleb_op	= 0x70fc,
+	stleh_op	= 0x70fd,
+	stlew_op	= 0x70fe,
+	stled_op	= 0x70ff,
 };
 
 enum reg3sa2_op {