From 6a0206897c83e1f3e4539d6a6c77149167f49626 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sun, 5 Sep 2021 12:17:38 +0200
Subject: stupidgcm: add BenchmarkCCall

gocryptfs/internal/stupidgcm$ go test -bench .
goos: linux
goarch: amd64
pkg: github.com/rfjakob/gocryptfs/v2/internal/stupidgcm
cpu: Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz
BenchmarkCCall-4   	15864030	        78.60 ns/op
PASS
ok  	github.com/rfjakob/gocryptfs/v2/internal/stupidgcm	1.898s
---
 internal/stupidgcm/common_test.go | 21 +++++++++++++++++++++
 internal/stupidgcm/openssl.go     |  6 ++++++
 internal/stupidgcm/openssl_aead.c |  5 +++++
 internal/stupidgcm/openssl_aead.h |  2 ++
 4 files changed, 34 insertions(+)

(limited to 'internal/stupidgcm')

diff --git a/internal/stupidgcm/common_test.go b/internal/stupidgcm/common_test.go
index a8080ca..589d974 100644
--- a/internal/stupidgcm/common_test.go
+++ b/internal/stupidgcm/common_test.go
@@ -208,3 +208,24 @@ func randBytes(n int) []byte {
 	}
 	return b
 }
+
+/*
+BenchmarkCCall benchmarks the overhead of calling from Go into C.
+Looks like things improved a bit compared to
+https://www.cockroachlabs.com/blog/the-cost-and-complexity-of-cgo/
+where they measured 171ns/op:
+
+$ go test -bench .
+goos: linux
+goarch: amd64
+pkg: github.com/rfjakob/gocryptfs/v2/internal/stupidgcm
+cpu: Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz
+BenchmarkCCall-4   	13989364	        76.72 ns/op
+PASS
+ok  	github.com/rfjakob/gocryptfs/v2/internal/stupidgcm	1.735s
+*/
+func BenchmarkCCall(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		noopCFunction()
+	}
+}
diff --git a/internal/stupidgcm/openssl.go b/internal/stupidgcm/openssl.go
index cb9845e..82ec0a1 100644
--- a/internal/stupidgcm/openssl.go
+++ b/internal/stupidgcm/openssl.go
@@ -108,3 +108,9 @@ func openSSLOpen(a *stupidAEADCommon, dst, iv, in, authData []byte) ([]byte, err
 	}
 	return append(dst, buf...), nil
 }
+
+// This functions exists to benchmark the C call overhead from Go.
+// See BenchmarkCCall for resuts.
+func noopCFunction() {
+	C.noop_c_function()
+}
diff --git a/internal/stupidgcm/openssl_aead.c b/internal/stupidgcm/openssl_aead.c
index 9dc6866..77898d5 100644
--- a/internal/stupidgcm/openssl_aead.c
+++ b/internal/stupidgcm/openssl_aead.c
@@ -176,3 +176,8 @@ int openssl_aead_open(
 
     return plaintextLen;
 }
+
+// This functions exists to benchmark the C call overhead from Go.
+void noop_c_function(void) {
+    return;
+}
diff --git a/internal/stupidgcm/openssl_aead.h b/internal/stupidgcm/openssl_aead.h
index 6a818b6..820beeb 100644
--- a/internal/stupidgcm/openssl_aead.h
+++ b/internal/stupidgcm/openssl_aead.h
@@ -27,3 +27,5 @@ int openssl_aead_open(
     const int ivLen,
     unsigned char* const plaintext,
     const int plaintextBufLen);
+
+void noop_c_function(void);
-- 
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