Hojun-Cho ecf0a84127 6l: dynamic linking with symbol versioning ...

Teach the linker to consume ET_DYN shared objects and emit a
dynamically-linked ELF executable. Snake et al. can now link
against libncurses + libc through the system dynamic loader.

Pipeline additions:

- dyn.c: read ET_DYN, parse .dynsym + DT_SONAME, walk
  .gnu.version_d / .gnu.version to learn each export's default
  version (skip hidden entries).
- pass.c: when an undefined sym is provided by some Lso,
  promote it to dynamic, assign a PLT slot, record the
  matched version on the Lsym.
- dynout.c: emit PT_INTERP + PT_DYNAMIC, .dynsym/.dynstr/.hash,
  .plt + .got.plt + .rela.plt, .gnu.version + .gnu.version_r,
  and the full DT_* set with DT_BIND_NOW. Patch PC32/PLT32
  references against dyn syms to point at their PLT stubs.
- main.c: -L<dir> and -l<name> flag parsing; resolve <name>
  via .so / .so.<N> / .a in libdir order, skipping GNU ld
  linker scripts (libc.so on most distros).
- ww driver: collect -l/-L (joined and split forms) and pass
  through to 6l.

Design choices:

- DT_BIND_NOW so the loader resolves all PLT slots at startup;
  no PLT0 lazy resolver stub.
- SysV .hash, not .gnu.hash. One bucket; loader scans the
  chain. Slow at scale, fine for snake-class binaries.
- Non-PIE at fixed 0x400000.
- No section headers — loader uses program headers, but
  readelf -V/-S won't display anything.

Symbol versioning is the only correctness item beyond the
basic PLT/GOT machinery: glibc symbols default to versions
later than GLIBC_2.2.5 (e.g. clock_gettime → GLIBC_2.17 for
the vDSO impl), and the loader rejects unversioned references
to those without a matching Vernaux entry.

test/wwc/810_dyn covers four cases: bare libc dyn call,
multi-PLT, clock_gettime versioning, and fn-pointer to FFI
binding (which exercises the codegen fixes from the parent
commit alongside the new linker path).

2026-05-11 09:42:27 +09:00

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