SchOS/tools/ksyms.pl

#!/usr/bin/perl
# SPDX-License-Identifier: GPL-2.0-or-later
#
# Turn `nm -n kernel` into a symbol table the kernel can carry with it.
#
# docs/architecture/debugging.md milestone D0. Everything the debugger prints is an
# address until this exists, and an address has to be resolved by hand against
# a disassembly that may not be the one that was running.
#
# Perl and not Python, deliberately: this runs on every kernel link, so it is
# on the critical path of a clean build, and tools/vectors.pl already makes
# perl a requirement there. The Makefile comment above include/gfx/logo.h says why
# that line is worth holding.
#
# Two modes:
#   (default)  read nm output on stdin, write a C file on stdout
#   --list     read nm output on stdin, write "addr name" lines -- used by the
#              Makefile to prove the two link passes agree
#
# The layout trick this depends on: .ksym is placed after .text and .rodata in
# kernel/kernel.ld, so adding the table to the image cannot move any of the
# text symbols that are *in* the table. Two passes, and the second is stable.
# The Makefile verifies that rather than trusting it.

use strict;
use warnings;

# hex() on a 64-bit kernel address is fine on any perl with 64-bit integers,
# which is every perl this will meet; the warning is about 32-bit ones.
no warnings q(portable);

my $list = (@ARGV && $ARGV[0] eq '--list');

my @sym;             # [addr, name]
my $textend = 0;

while (my $line = <STDIN>) {
    chomp $line;
    # "ffff800000100000 T begin". Symbols with no address print as spaces and
    # fall out here on the field count.
    my ($addr, $type, $name) = $line =~ /^([0-9a-fA-F]+)\s+(\S)\s+(\S+)$/
        or next;

    # etext is the end of the text section, and it is the only non-function we
    # want: without it a lookup of an address past the last function walks off
    # the end of the table and names whatever was linked last.
    if ($name eq 'etext') {
        $textend = hex($addr);
        next;
    }

    # t/T are text, w/W are weak text. Everything else is data, bss or absolute
    # and naming it would make a code address resolve to a variable.
    next unless $type =~ /^[tTwW]$/;

    # Compiler-local labels. They have no meaning outside one translation unit
    # and they would shadow the function they sit inside.
    next if $name =~ /^\.L/;
    next if $name =~ /\$/;

    push @sym, [hex($addr), $name, $type];
}

die "ksyms: no text symbols on stdin\n" unless @sym;

# nm -n sorts numerically, but ties come out in whatever order the symbol table
# had them. Prefer the global at a shared address: `begin` and `mboot_header`
# are the same byte, and naming that byte `begin` tells you nothing.
my @uniq;
for my $s (@sym) {
    if (@uniq && $uniq[-1][0] == $s->[0]) {
        $uniq[-1] = $s if $s->[2] =~ /^[TW]$/ && $uniq[-1][2] =~ /^[tw]$/;
        next;
    }
    push @uniq, $s;
}
@sym = @uniq;

$textend = $sym[-1][0] + 0x1000 unless $textend;

if ($list) {
    printf "%016x %s\n", $_->[0], $_->[1] for @sym;
    exit 0;
}

my $base = $sym[0][0];
for my $s (@sym) {
    die sprintf("ksyms: symbol %s at %x is more than 4 GB above the base\n",
                $s->[1], $s->[0])
        if $s->[0] - $base > 0xffffffff;
}

# Offsets into the name blob, computed here so the kernel does not have to
# scan for NULs at boot.
my @off;
my $cur = 0;
for my $s (@sym) {
    push @off, $cur;
    $cur += length($s->[1]) + 1;
}

my $n = scalar @sym;

print <<"HDR";
// Generated by tools/ksyms.pl from the first link pass. Do not edit.
//
// See docs/architecture/debugging.md, milestone D0, and kernel/core/ksym.c for the
// lookup that reads this. Everything lands in .ksym, which kernel/kernel.ld
// places after .text and .rodata so that carrying the table cannot move the
// addresses recorded in it.

#include "core/types.h"

#define KSYM_SECTION __attribute__((section(".ksym"), used))

KSYM_SECTION const uint32 ksym_count   = ${n}u;
KSYM_SECTION const uint64 ksym_base    = 0x${\ sprintf("%x", $base) }ULL;
KSYM_SECTION const uint64 ksym_textend = 0x${\ sprintf("%x", $textend) }ULL;

// Offsets from ksym_base rather than absolute addresses: the kernel spans
// about a megabyte, so 32 bits is plenty and it halves the table.
KSYM_SECTION const uint32 ksym_addr[${n}] = {
HDR

for (my $i = 0; $i < $n; $i += 8) {
    my $end = $i + 7; $end = $n - 1 if $end > $n - 1;
    print "  ", join(",", map { sprintf("0x%08x", $sym[$_][0] - $base) } ($i .. $end)), ",\n";
}

print "};\n\nKSYM_SECTION const uint32 ksym_nameoff[${n}] = {\n";

for (my $i = 0; $i < $n; $i += 8) {
    my $end = $i + 7; $end = $n - 1 if $end > $n - 1;
    print "  ", join(",", map { sprintf("%6d", $off[$_]) } ($i .. $end)), ",\n";
}

print "};\n\nKSYM_SECTION const char ksym_names[] =\n";

for my $s (@sym) {
    my $name = $s->[1];
    $name =~ s/([\\"])/\\$1/g;
    print "  \"$name\\0\"\n";
}

print ";\n";