From 009e92288be77829272bf10984bbac0828342377 Mon Sep 17 00:00:00 2001
From: Alban Crequy <albancrequy@linux.microsoft.com>
Date: Mon, 26 Aug 2024 11:56:22 +0200
Subject: [PATCH] New architecture: wasm

cilium/ebpf currently does not compile to wasm with tinygo. This patch
makes it compile.

I am working on a website where users can submit ebpf binaries (either
in ELF format or as an Inspektor Gadget export) and the website will
parse the ebpf binary client-side with wasm. The wasm code is written in
Go, using cilium/ebpf and is compiled with tinygo.

My wasm code uses ebpf.LoadCollectionSpecFromReader() to display
information about the ebpf binary. But it will not call
ebpf.NewCollection() because the wasm/javascript environment in the
browser cannot interact with the Linux kernel.

Signed-off-by: Alban Crequy <albancrequy@linux.microsoft.com>
---
 btf/btf.go            | 12 ++++++++++--
 internal/endian_le.go |  2 +-
 internal/io.go        |  3 ++-
 map.go                |  6 +++---
 syscalls.go           |  3 ++-
 5 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/btf/btf.go b/btf/btf.go
index 671f680b2..20bed62c6 100644
--- a/btf/btf.go
+++ b/btf/btf.go
@@ -632,8 +632,16 @@ func (s *Spec) TypeByName(name string, typ interface{}) error {
 		wanted = typPtr.Elem().Type()
 	}
 
-	if !wanted.AssignableTo(typeInterface) {
-		return fmt.Errorf("%T does not satisfy Type interface", typ)
+	switch wanted {
+	case reflect.TypeOf((**Datasec)(nil)).Elem():
+		// Those types are already assignable to Type. No need to call
+		// AssignableTo. Avoid it when possible to workaround
+		// limitation in tinygo:
+		// https://github.com/tinygo-org/tinygo/issues/4277
+	default:
+		if !wanted.AssignableTo(typeInterface) {
+			return fmt.Errorf("%T does not satisfy Type interface", typ)
+		}
 	}
 
 	types, err := s.AnyTypesByName(name)
diff --git a/internal/endian_le.go b/internal/endian_le.go
index 6dcd916d5..d833ea764 100644
--- a/internal/endian_le.go
+++ b/internal/endian_le.go
@@ -1,4 +1,4 @@
-//go:build 386 || amd64 || amd64p32 || arm || arm64 || loong64 || mipsle || mips64le || mips64p32le || ppc64le || riscv64
+//go:build 386 || amd64 || amd64p32 || arm || arm64 || loong64 || mipsle || mips64le || mips64p32le || ppc64le || riscv64 || wasm
 
 package internal
 
diff --git a/internal/io.go b/internal/io.go
index 1eaf4775a..6ccbd8c24 100644
--- a/internal/io.go
+++ b/internal/io.go
@@ -27,8 +27,9 @@ func NewBufferedSectionReader(ra io.ReaderAt, off, n int64) *bufio.Reader {
 	// of a file into memory. bufio.NewReader uses a hardcoded default buffer
 	// of 4096. Allow arches with larger pages to allocate more, but don't
 	// allocate a fixed 4k buffer if we only need to read a small segment.
+	pageSize := int64(4096)
 	buf := n
-	if ps := int64(os.Getpagesize()); n > ps {
+	if ps := pageSize; n > ps {
 		buf = ps
 	}
 
diff --git a/map.go b/map.go
index d0ea05d4a..0a66d3386 100644
--- a/map.go
+++ b/map.go
@@ -6,7 +6,7 @@ import (
 	"fmt"
 	"io"
 	"math/rand"
-	"os"
+	//"os"
 	"path/filepath"
 	"reflect"
 	"slices"
@@ -507,7 +507,7 @@ func handleMapCreateError(attr sys.MapCreateAttr, spec *MapSpec, err error) erro
 	// BPF_MAP_TYPE_RINGBUF's max_entries must be a power-of-2 multiple of kernel's page size.
 	if errors.Is(err, unix.EINVAL) &&
 		(attr.MapType == sys.BPF_MAP_TYPE_RINGBUF || attr.MapType == sys.BPF_MAP_TYPE_USER_RINGBUF) {
-		pageSize := uint32(os.Getpagesize())
+		pageSize := uint32(4096)
 		maxEntries := attr.MaxEntries
 		if maxEntries%pageSize != 0 || !internal.IsPow(maxEntries) {
 			return fmt.Errorf("map create: %w (ring map size %d not a multiple of page size %d)", err, maxEntries, pageSize)
@@ -950,7 +950,7 @@ func (m *Map) nextKey(key interface{}, nextKeyOut sys.Pointer) error {
 }
 
 var mmapProtectedPage = sync.OnceValues(func() ([]byte, error) {
-	return unix.Mmap(-1, 0, os.Getpagesize(), unix.PROT_NONE, unix.MAP_ANON|unix.MAP_SHARED)
+	return unix.Mmap(-1, 0, 4096, unix.PROT_NONE, unix.MAP_ANON|unix.MAP_SHARED)
 })
 
 // guessNonExistentKey attempts to perform a map lookup that returns ENOENT.
diff --git a/syscalls.go b/syscalls.go
index 0766e7dd6..d0ea244f4 100644
--- a/syscalls.go
+++ b/syscalls.go
@@ -27,7 +27,8 @@ var (
 // invalidBPFObjNameChar returns true if char may not appear in
 // a BPF object name.
 func invalidBPFObjNameChar(char rune) bool {
-	dotAllowed := objNameAllowsDot() == nil
+	//dotAllowed := objNameAllowsDot() == nil
+	dotAllowed := true
 
 	switch {
 	case char >= 'A' && char <= 'Z':