[Bug ld/24576] New: Feature request: error out when passed the same linker script with -T and as an object file

[jwerner at chromium dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=24576

            Bug ID: 24576
           Summary: Feature request: error out when passed the same linker
                    script with -T and as an object file
           Product: binutils
           Version: 2.32
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: jwerner at chromium dot org
  Target Milestone: ---

This is just a small feature request to help people notice mistakes. When using
Makefiles to build things, it's easy to write rules like:

linker_script.ld: linker_script.ld.S
  <preprocess with CPP>

my.elf: $(myobjects) $(somelibrary) linker_script.ld
  $(LD) $(LDFLAGS) -o $@ -T linker_script.ld $^

There's a subtle error in the above: sincer linker_script.ld is part of the
prerequisites, it will be part of the $^ variable expansion, despite already
being listed explicitly for the -T flag. This means the linker will both use it
as the default linker script and then use it again to "augment" that script.
This will often not lead to an obvious error but cause all kinds of subtle
hijinks with symbol placement. The resulting binary may still run and contain
hard to understand rare errors.

I don't think there could ever be a valid use case where you'd want to pass the
same file as an argument to -T and as an augment linker script later on, so
could you just add a check to error out somewhere if that happens? That could
save the people running into this a lot of headache.

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