vdso linker scripts: explicitly specify output arch and target

[emaste]

LGTM for lld, which ignores OUTPUT_ARCH and does not do much with TARGET

void ScriptParser::readOutputArch() {
  // OUTPUT_ARCH is ignored for now.
  expect("(");
  while (!errorCount() && !consume(")"))
    skip();
}

void ScriptParser::readTarget() {
  // TARGET(foo) is an alias for "--format foo". Unlike GNU linkers,
  // we accept only a limited set of BFD names (i.e. "elf" or "binary")
  // for --format. We recognize only /^elf/ and "binary" in the linker
  // script as well.
  expect("(");
  StringRef tok = next();
  expect(")");

  if (tok.startswith("elf"))
    config->formatBinary = false;
  else if (tok == "binary")
    config->formatBinary = true;
  else
    setError("unknown target: " + tok);
}

from ld docs:

• OUTPUT_ARCH ( bfdname ) Specify a particular output machine architecture, with one of the names used by the BFD back-end routines (see section BFD). This command is often unnecessary; the architecture is most often set implicitly by either the system BFD configuration or as a side effect of the OUTPUT_FORMAT command.
• OUTPUT_FORMAT ( bfdname ) When ld is configured to support multiple object code formats, you can use this command to specify a particular output format. bfdname is one of the names used by the BFD back-end routines (see section BFD). The effect is identical to the effect of the `--oformat' command-line option. This selection affects only the output file; the related command TARGET affects primarily input files.

[kib]

Even more weird. I remember I had to add OUTPUT_ARCH() for ia32 vdso. Might be it was due to ld.bfd. But John reports that it cannot be built with ld.bfd anyway.

[jhb]

Only tried with the TARGET line added to vdso_amd64_ia32.ldscript and that did work.

[emaste]

IMO it's worth noting in the commit (or maybe even a comment in the file) that these are for ld.bfd and lld doesn't do much with them, the only thing it does is produce ELF or binary based on TARGET

[kib]

In D34157#773704, @jhb wrote:

Only tried with the TARGET line added to vdso_amd64_ia32.ldscript and that did work.

Do you mean, you want me to remove OUTPUT_ARCH() from both scripts?

[kib]

Add comments.

[jhb]

In D34157#773726, @kib wrote:

In D34157#773704, @jhb wrote:

Only tried with the TARGET line added to vdso_amd64_ia32.ldscript and that did work.

Do you mean, you want me to remove OUTPUT_ARCH() from both scripts?

No, I didn't try with the OUTPUT_ARCH removed from the i386 script (I meant I only tried that part of your patch and didn't change vdso_amd64.ldscript). I think you can either merge as-is or only add the change to vdso_amd64_ia32.ldscript and leave vdso_amd64.ldscript alone.