The ELF spec says:
> STT_FILE: Conventionally, the symbol's name gives the name of the source file associated with the object file. A file symbol has STB_LOCAL binding, its section index is SHN_ABS, and it precedes the other STB_LOCAL symbols for the file, if it is present.
For a local symbol, the preceding STT_FILE symbol is almost always in the same
file[1]. GNU addr2line uses this heuristic to retrieve the filename associated
with a local symbol (e.g. internal linkage functions in C/C++).
GNU addr2line can assign STT_FILE filename to a non-local symbol, too, but the trick
only works if no regular symbol precede STT_FILE. This patch does not implement this corner case
(not useful for most executables which have more than one files).
In case of filename mismatch between .debug_line & .symtab, arbitrarily make .debug_line win.
[1]: LLD does not synthesize STT_FILE symbols
(https://bugs.llvm.org/show_bug.cgi?id=48023 see also
https://sourceware.org/bugzilla/show_bug.cgi?id=26822). An assembly file
without `.file` directives can cause mis-attribution. This is an edge case.
Differential Revision: https://reviews.llvm.org/D95927
Fangrui Song