Reflection over the callstack reports incorrect file/line information for init()
functions that span source files.  The filename is always that of the source file
containing the first statement of init(), and the line number is garbage, often negative.

The compiler and linker are doing the right thing; the problem is in runtime/symtab.c,
which is making the simplifying assumption that "we don't need the full generality
of the z entry history stack because there are no includes in go", i.e. every
function (Func) is associated with exactly one file.  Because init() can be spread
across files, this assumption is false.

Luckily the public interfaces are all sound, but the following changes are required:

(1) symtab.c: push each 'z' symbol on a spaghetti stack associated with the object file.
 Don't throw the previous stack away each time we encounter a new start-of-object
(z.value=1) symbol.
(2) symtab.c: to convert a composite line number (z.value) to a source line, invert the
spaghetti stack to a tree and visit it depth-first until the file containing the z.value
is found; then subtract the deltas for each file on the path via which it was found.
(3) extern.go: reflect the changes to the underlying C code.

While you're there, you may want to support 'Z' symbols (#line directives).

Attachments:

1. bug.tar.bz2 (678 bytes)