macro: create .notes.perlmod.package section in libraries

So all the macro-supported packages can be listed in the ELF file.
This way all the available packages in a library can be viewed with
`readelf -W -n libfoo.so`. In the future we can also embed metadata in
there.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

perlmod-bin/genpackage.pl

@@ -34,6 +34,10 @@ my $opts = {
         'PATH',
         "Path to additional perl code to include in the package after the 'use' statements",
     ],
+    'from-notes' => [
+        undef,
+        "Read the package list from ELF notes sections",
+    ],
 };
 
 sub help {
@@ -43,7 +47,7 @@ sub help {
     print {$fd} "mandatory OPTIONS are:\n";
     for my $o (sort keys %$opts) {
         my ($arg, $desc) = $opts->{$o}->@*;
-        my $p = "--$o=$arg";
+        my $p = defined($arg) ? "--$o=$arg" : "--$o";
         printf {$fd} "  %20s   %s\n", $p, $desc;
     }
 }
@@ -74,6 +78,13 @@ ARGPARSE: while (@ARGV) {
         } else {
             next;
         };
+
+        if (!defined($opts->{$o}->[0])) {
+            unshift @ARGV, $arg;
+            $params->{$o} = 1;
+            next ARGPARSE;
+        }
+
         die "--$o requires an argument\n" if !defined($arg);
         if (ref($params->{$o}) eq 'ARRAY') {
             push $params->{$o}->@*, $arg;
@@ -99,7 +110,8 @@ my $lib_prefix = $params->{'lib-prefix'}
     or die "missing --lib-prefix parameter\n";
 my $lib = $params->{'lib'}
     or die "missing --lib parameter\n";
-my $lib_tag = $params->{'lib-tag'};
+my $lib_tag = $params->{'lib-tag'}
+    or die "missing --lib-tag parameter\n";
 my $debug_libpath = $params->{'debug-libpath'} // '';
 my $extra_code = '';
 for my $file ($params->{'include-file'}->@*) {
@@ -108,6 +120,7 @@ for my $file ($params->{'include-file'}->@*) {
     die "error reading '$file': $!\n" if !defined($more);
     $extra_code .= $more;
 }
+my $from_notes = $params->{'from-notes'};
 
 sub pkg2file {
     return ($_[0] =~ s@::@/@gr) . ".pm";
@@ -225,6 +238,29 @@ if ($lib ne '-') {
     close($fh);
 }
 
+if ($from_notes) {
+    die "missing library file to read packages from\n" if !@ARGV;
+    die "--from-notes requires exactly one library\n" if @ARGV > 1;
+
+    open my $fh, '<', $ARGV[0] or die "failed to open $ARGV[0] for reading: $!\n";
+    my $fd = fileno($fh);
+    my $data = `objcopy -O binary --only-section .note.perlmod.package $ARGV[0] /dev/stdout`;
+    close($fh);
+
+    my @packages;
+    while (length($data)) {
+        my ($name_size, $desc_size, $ty) = unpack('LLL', substr($data, 0, 3*4, ''));
+        die "unexpected description in package note - incompatible perlmod version?\n"
+            if $desc_size;
+        my $name = substr($data, 0, $name_size, '');
+        my $desc = substr($data, 0, $desc_size, '');
+        print("Found package '$name'\n");
+        push @packages, $name;
+    }
+    die "trailing data in notes section\n" if length($data);
+    @ARGV = @packages;
+}
+
 for my $package (@ARGV) {
     my $path = ($package =~ s@::@/@gr) . ".pm";
 

perlmod-macro/src/package.rs

@@ -107,6 +107,9 @@ impl Package {
             });
         }
 
+        let package_name_bytes =
+            syn::LitByteStr::new(self.attrs.package_name.as_bytes(), Span::call_site());
+        let package_name_len = self.attrs.package_name.len();
         let bootstrap_name = format!("boot_{}", self.attrs.package_name).replace("::", "__");
         let bootstrap_ident = Ident::new(&bootstrap_name, Span::call_site());
 
@@ -120,7 +123,13 @@ impl Package {
             pub extern "C" fn #bootstrap_ident(
                 _cv: Option<&::perlmod::ffi::CV>,
             ) {
+                #[used]
+                #[link_section = ".note.perlmod.package"]
+                static PACKAGE_ENTRY: ::perlmod::__private__::ElfNote<{#package_name_len}> =
+                    ::perlmod::__private__::ElfNote::new_package(*#package_name_bytes);
+
                 static ONCE: ::std::sync::Once = ::std::sync::Once::new();
+
                 ONCE.call_once(|| {
                     unsafe {
                         use ::perlmod::ffi::RSPL_newXS_flags;

perlmod/src/elf_notes.rs

@@ -0,0 +1,32 @@
+//! The `#[package]` macro stores package lists in ELF file note sections.
+//! This is the implementation for this.
+//!
+//! This is private and not meant to be a public API.
+
+/*
+#[repr(C, packed)]
+pub struct Info {
+    extra stuff
+}
+*/
+
+#[repr(C, packed)]
+pub struct ElfNote<const N: usize> {
+    pub name_size: u32,
+    pub desc_size: u32,
+    pub ty: u32,
+    pub name: [u8; N],
+    //pub desc: Info,
+}
+
+impl<const N: usize> ElfNote<{ N }> {
+    pub const fn new_package(name: [u8; N]) -> Self {
+        Self {
+            name_size: N as u32,
+            desc_size: 0, // size_of::<Info>()
+            ty: 0,
+            name,
+            //desc: Info::new(),
+        }
+    }
+}

perlmod/src/lib.rs

@@ -113,3 +113,12 @@ pub use perlmod_macro::package;
 ///
 /// For an example on making blessed objects, see [`Value::bless_box`](Value::bless_box()).
 pub use perlmod_macro::export;
+
+mod elf_notes;
+
+#[doc(hidden)]
+pub mod __private__ {
+    //! This is private and not meant to be a public API and thus semver exempt.
+
+    pub use super::elf_notes::ElfNote;
+}