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Enable building with lld #75

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Commits on Jan 27, 2024

  1. libsel4utils: Fix TLS page fault if PT_PHDR exists 

    PT_PHDR is emitted by ld.lld but not ld.bfd. This segment should only
exist if the program header *is* part of the program memory image itself
(which is not the case in seL4, as it copies the program header in the
stack). This is important as muslc’s TLS init is relying on the existence
of PT_PHDR to get the base address of the image in memory and from that,
it calculates the TLS base for the source ELF. The calculation will be
wrong in seL4 as the program header is copied in the stack; thus it may
trigger a page fault if the new TLS base is not mapped, or affects the
integrity of programs relying on TLS variables (e.g., those with
__thread).

By setting PT_PHDR's segment to PT_NULL, muslc will skip this search and
won't do any relocations for the TLS segment which is part of the
loaded ELF image itself, thus getting the correct mapped address.

Sponsored by: DARPA.

Signed-off-by: Hesham Almatary <hesham.almatary@cl.cam.ac.uk>
    @heshamelmatary
    heshamelmatary committed Jan 27, 2024
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  2. libsel4test: retain _test_type and _test_case 

    unused attribute does not prevent the sections from being
garbage-collected during link-time optimisation. This may trigger
undefined references errors to [__start|__stop]_test_case symbols
that are expected to be emitted by the linker anyway.

Adding "retain" attribute makes sure that the section and its
associated symbols are kept regardless of linker's garbage
collection. Another fix could be adding "nostart-stop-gc" to the
linker flags, but since it is only one section (_test_case)
where its __start/__stop symbols are references, adding retain to
it makes more sense. This additional functionality requires
binutils version 2.36 or later.

Sponsored by: DARPA.

Signed-off-by: Hesham Almatary <hesham.almatary@cl.cam.ac.uk>
    @heshamelmatary
    heshamelmatary committed Jan 27, 2024
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