debug: fix edge cases in macOS debug symbol lookup

This commit fixes two related things:

1. If the loop goes all the way through the slice without a match, on
   the last iteration `mid == symbols.len - 1` which causes
   `&symbols[mid + 1]` to be out of bounds. End one step before that
   instead.

2. If the address we're looking for is greater than the address of the
   last symbol in the slice, we now match it to that symbol. Previously,
   we would miss this case since we only matched if the address was _in
   between_ the address of two symbols.

Author: schmee

lib/std/debug.zig

@@ -6,6 +6,7 @@ const io = std.io;
 const os = std.os;
 const fs = std.fs;
 const process = std.process;
+const testing = std.testing;
 const elf = std.elf;
 const DW = std.dwarf;
 const macho = std.macho;
@@ -559,7 +560,7 @@ pub const TTY = struct {
 
 fn machoSearchSymbols(symbols: []const MachoSymbol, address: usize) ?*const MachoSymbol {
     var min: usize = 0;
-    var max: usize = symbols.len;
+    var max: usize = symbols.len - 1;
     while (min < max) {
         const mid = min + (max - min) / 2;
         const curr = &symbols[mid];
@@ -572,9 +573,36 @@ fn machoSearchSymbols(symbols: []const MachoSymbol, address: usize) ?*const Mach
             return curr;
         }
     }
+
+    const max_sym = &symbols[symbols.len - 1];
+    if (address >= max_sym.address())
+        return max_sym;
+
     return null;
 }
 
+test "machoSearchSymbols" {
+    const symbols = [_]MachoSymbol{
+        .{ .addr = 100, .strx = undefined, .size = undefined, .ofile = undefined },
+        .{ .addr = 200, .strx = undefined, .size = undefined, .ofile = undefined },
+        .{ .addr = 300, .strx = undefined, .size = undefined, .ofile = undefined },
+    };
+
+    try testing.expectEqual(@as(?*const MachoSymbol, null), machoSearchSymbols(&symbols, 0));
+    try testing.expectEqual(@as(?*const MachoSymbol, null), machoSearchSymbols(&symbols, 99));
+    try testing.expectEqual(&symbols[0], machoSearchSymbols(&symbols, 100).?);
+    try testing.expectEqual(&symbols[0], machoSearchSymbols(&symbols, 150).?);
+    try testing.expectEqual(&symbols[0], machoSearchSymbols(&symbols, 199).?);
+
+    try testing.expectEqual(&symbols[1], machoSearchSymbols(&symbols, 200).?);
+    try testing.expectEqual(&symbols[1], machoSearchSymbols(&symbols, 250).?);
+    try testing.expectEqual(&symbols[1], machoSearchSymbols(&symbols, 299).?);
+
+    try testing.expectEqual(&symbols[2], machoSearchSymbols(&symbols, 300).?);
+    try testing.expectEqual(&symbols[2], machoSearchSymbols(&symbols, 301).?);
+    try testing.expectEqual(&symbols[2], machoSearchSymbols(&symbols, 5000).?);
+}
+
 /// TODO resources https://github.com/ziglang/zig/issues/4353
 pub fn printSourceAtAddress(debug_info: *DebugInfo, out_stream: anytype, address: usize, tty_config: TTY.Config) !void {
     const module = debug_info.getModuleForAddress(address) catch |err| switch (err) {