Commit `b47530b9fe`

Jacob G-W <jacoblevgw@gmail.com>

2022-01-02 21:52:25

plan9: fix .z symbol in debuginfo

This allows the `acid` debugger on plan9 to be used to debug a zig source file without patching `acid`! The patch adds a second `z` symbol. This z symbol has a value of 0, which means that it pops the history stack. We put a very large number for the value of the second symbol because it has to be at least as large as the linecount of the file. The debuginfo format is meant to be used with c files, where the stack would look something like this: ``` -> Line: 0x1 (1) Name: 0x1/0x2/0x3/0xe/0x13/0x1b (/sys/src/libc/port/malloc.c) -> Line: 0x2 (2) Name: 0x1/0x6/0x7/0x8 (/amd64/include/u.h) -> Line: 0x4f (79) Name: () -> Line: 0x50 (80) Name: 0x1/0x2/0x7/0x9 (/sys/include/libc.h) -> Line: 0x358 (856) Name: () -> Line: 0x359 (857) Name: 0x1/0x2/0x7/0x1c (/sys/include/pool.h) -> Line: 0x392 (914) Name: () -> Line: 0x393 (915) Name: 0x1/0x2/0x7/0x1d (/sys/include/tos.h) -> Line: 0x3ab (939) Name: () -> Line: 0x4eb (1259) Name: () ``` however in zig, we do not use includes and .h files, so we only need the first and last items in the stack: the source file that the symbols belong to, and the pop symbol with a null name and a value of the total linecount of the preprocessed source. Since there is no preprocessing in zig, we just make the linecount very large. There do not appear to be any downsides to this approach. If this causes a bug in the future, a simple fix would be to make the pop symbol just have the value of how many newlines are in the source file.

master

1 parent 1d55e4c

Changed files (1)

src

link

Plan9.zig

@@ -172,6 +172,7 @@ fn putFn(self: *Plan9, decl: *Module.Decl, out: FnDeclOutput) !void {
         // each file gets a symbol
         fn_map_res.value_ptr.* = .{
             .sym_index = blk: {
+                try self.syms.append(gpa, undefined);
                 try self.syms.append(gpa, undefined);
                 break :blk @intCast(u32, self.syms.items.len - 1);
             },
@@ -194,11 +195,17 @@ fn putFn(self: *Plan9, decl: *Module.Decl, out: FnDeclOutput) !void {
         // null terminate
         try a.append(0);
         const final = a.toOwnedSlice();
-        self.syms.items[fn_map_res.value_ptr.sym_index] = .{
+        self.syms.items[fn_map_res.value_ptr.sym_index - 1] = .{
             .type = .z,
             .value = 1,
             .name = final,
         };
+        self.syms.items[fn_map_res.value_ptr.sym_index] = .{
+            .type = .z,
+            // just put a giant number, no source file will have this many newlines
+            .value = std.math.maxInt(u32),
+            .name = &.{ 0, 0 },
+        };
     }
 }
 
@@ -705,7 +712,8 @@ pub fn writeSyms(self: *Plan9, buf: *std.ArrayList(u8)) !void {
         var it_file = self.fn_decl_table.iterator();
         while (it_file.next()) |fentry| {
             var symidx_and_submap = fentry.value_ptr;
-            // write the z symbol
+            // write the z symbols
+            try self.writeSym(writer, self.syms.items[symidx_and_submap.sym_index - 1]);
             try self.writeSym(writer, self.syms.items[symidx_and_submap.sym_index]);
 
             // write all the decls come from the file of the z symbol

Commit b47530b9fe

Commit `b47530b9fe`