Range lists, zero-length functions, linker gc

Alan Modra amodra@gmail.com
Wed Jun 3 03:10:40 GMT 2020


On Tue, Jun 02, 2020 at 11:06:10AM -0700, David Blaikie via Binutils wrote:
> On Tue, Jun 2, 2020 at 9:50 AM Mark Wielaard <mark@klomp.org> wrote:
> > where I
> > would argue the compiler simply needs to make sure that if it generates
> > code in separate sections it also should create the DWARF separate
> > section (groups).
> 
> I don't think that's practical - the overhead, I believe, is too high.
> Headers for each section contribution (ELF headers but DWARF headers
> moreso - having a separate .debug_addr, .debug_line, etc section for
> each function would be very expensive) would make for very large
> object files.

With a little linker magic I don't see the neccesity of duplicating
the DWARF headers.  Taking .debug_line as an example, a compiler could
emit the header, opcode, directory and file tables to a .debug_line
section with line statements for function foo emitted to
.debug_line.foo and for bar to .debug_line.bar, trusting that the
linker will combine these sections in order to create an output
.debug_line section.  If foo code is excluded then .debug_line.foo
info will also be dropped if section groups are used.

-- 
Alan Modra
Australia Development Lab, IBM


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