From 068ff9301dc3b5d03b7ecfab47fb7947d7190b82 Mon Sep 17 00:00:00 2001
From: smcio <shaun@darkwaves.io>
Date: Wed, 5 Jul 2023 21:06:41 +0100
Subject: [PATCH] sealevel: modify memcmp syscall

---
 fixtures/sbpf/memcmp_not_matched.so | Bin 2384 -> 2512 bytes
 pkg/sealevel/sealevel_test.go       |   6 +++---
 pkg/sealevel/syscalls_mem.go        |   2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fixtures/sbpf/memcmp_not_matched.so b/fixtures/sbpf/memcmp_not_matched.so
index e2fb0b2901b93463e908cec89bf46ee46fc08ea9..8b6eee32a663bd79f3545e547dedc1758c78ad33 100755
GIT binary patch
delta 625
zcmZ8eK}!Nb6yBNH-P!fhx)SOk*KX25Q9;RrSf_|c11Y+MmO^;wAO#CujOZ97?+>VS
z5;}D6;17_J{y=mrI^?ZGU^BZjB|Vt^_I>ZYZ{IgNu_vLM1h!~*CAU^XiWd?U%g;Hj
zveUtS{vXFat&F?<@TS+v2|mF?pcIuT#kr==PKEI1c?68sZTT%;im+ZnU>C(!Kg24W
zuJ^xZ92e072PMMxeVVIZF&i@$9uIfO$z0D>Is3}0-Y9$22fo^p?Kef(au$I{bV&}6
z8c@X@*ujP1cDWjFH&4&nC(TBZ&%z6i27AJ+E!0L}633<@<2Joep+I8Dg?+MzN^nmc
zGcK+^1XB`*PtrqQaG^Tb!Z1*iIDz3=J-`NrjFv<jP}jmyd0|p?nZ4KwQcBR({sgn0
z;6yt|S=iEVQ4OYgDkyJN;uz926_AP*0xg;g$Ump3Fr+!t72aHUqxoN_((wq=MjqER
YXc<N9YA|GQti!ueG#`ZTGEAxS1B|s_Bme*a

delta 565
zcmZWmJx>Bb5Z&4PU=N$)hyfZdSQ!dHFc6I)(M}tPg;p9-8|^5KrLjNqet?o#nV5jB
z{s9vU5*y32GgOuoM%?A@gy1BTH}huq?Y_()IdHsX?wOr@b+bfl5)m>x=oPKYZ1SL=
zM=zk6*XgEqJT2(vu^Ea-7>O%QQ>Gt^PZ6B9oVSoxqG?$-Irb>K_B=zky5D0pUL;Ea
zOUsvTX6Dz@##qLL#{;?ifa8a*plj=R;@b<yC#Nl$E9J^68d@e%Qf6g10k9q}G}lp|
zR1u-4;a<y<z>Bs|HgdXaeFZ025-mN2BmEY(VRN6bWEA*_uxlLhcfzAlpfo;=R3<VT
z-eWmgIE<K$ggKR~Oyrv8C6)1N-cbqdSTXT$3+Ts+@kr6<7{;pc=@yU|RZE1<1kOb5
i&u8SfhrXzBU&m0?`AA3Js`F0+=T_a?2wgYO7Va;MGgnyv

diff --git a/pkg/sealevel/sealevel_test.go b/pkg/sealevel/sealevel_test.go
index 51c8826..5370ec7 100644
--- a/pkg/sealevel/sealevel_test.go
+++ b/pkg/sealevel/sealevel_test.go
@@ -313,10 +313,10 @@ func TestInterpreter_Memcmp_Matches(t *testing.T) {
 }
 
 // The TestInterpreter_Memcmp_Does_Not_Match function tests that the memcmp
-// syscall works as expected by comparing the string literals "abcdabcd1234"
-// and "BLAHabcd1234"
+// syscall works as expected by comparing the string literals "Bbcdabcd1234"
+// and "aLAHabcd1234"
 // The expected result is that the two strings do not match and the difference
-// between the first non-matching characters (0x61 - 0x42 = 0x1f) is returned,
+// between the first non-matching characters (0x42 - 0x61 = -0x1f) is returned,
 // and the program checks these and returns messages accordingly.
 func TestInterpreter_Memcmp_Does_Not_Match(t *testing.T) {
 	loader, err := loader.NewLoaderFromBytes(fixtures.Load(t, "sbpf", "memcmp_not_matched.so"))
diff --git a/pkg/sealevel/syscalls_mem.go b/pkg/sealevel/syscalls_mem.go
index 4450b4a..5afcaaf 100644
--- a/pkg/sealevel/syscalls_mem.go
+++ b/pkg/sealevel/syscalls_mem.go
@@ -87,7 +87,7 @@ func SyscallMemcmpImpl(vm sbpf.VM, addr1, addr2, n, resultAddr uint64, cuIn int)
 		b1 := slice1[count]
 		b2 := slice2[count]
 		if b1 != b2 {
-			cmpResult = int32(b1 - b2)
+			cmpResult = int32(b1) - int32(b2)
 			break
 		}
 	}