[PATCH] [ELF] Fix allocation of program headers

[Patrick Oppenlander via llvm-commits]

Hi,

I'm posting this here following the one-off patch recommendations from
the LLVM developer policy.

While porting an embedded project to LLVM/clang I ran into a problem
with how lld allocates program headers into the program image.

The target requires a link script similar to:

PHDRS {
    ph1 PT_LOAD FILEHDR PHDRS;
    ph2 PT_LOAD;
}

MEMORY {
    mem1 : ORIGIN = 0x1000000000000000, LENGTH = 64K
    mem2 : ORIGIN = 0, LENGTH = 128K
}

SECTIONS {
    .text ORIGIN(mem1) + SIZEOF_HEADERS : {
        *(.text*)
    } >mem1 :ph1
    .data : {
        *(.data*)
    } >mem2 :ph2
}

GNU ld happily links this, but unfortunately lld fails with "error:
could not allocate headers".

I've attached a patch for review which is my attempt to address the
issue. It passes the lld testsuite and includes a new test case.

Kind regards,

Patrick
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