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this overhaul further reduces the amount of arch-specific code needed
by the dynamic linker and removes a number of assumptions, including:
- that symbolic function references inside libc are bound at link time
via the linker option -Bsymbolic-functions.
- that libc functions used by the dynamic linker do not require
access to data symbols.
- that static/internal function calls and data accesses can be made
without performing any relocations, or that arch-specific startup
code handled any such relocations needed.
removing these assumptions paves the way for allowing libc.so itself
to be built with stack protector (among other things), and is achieved
by a three-stage bootstrap process:
1. relative relocations are processed with a flat function.
2. symbolic relocations are processed with no external calls/data.
3. main program and dependency libs are processed with a
fully-functional libc/ldso.
reduction in arch-specific code is achived through the following:
- crt_arch.h, used for generating crt1.o, now provides the entry point
for the dynamic linker too.
- asm is no longer responsible for skipping the beginning of argv[]
when ldso is invoked as a command.
- the functionality previously provided by __reloc_self for heavily
GOT-dependent RISC archs is now the arch-agnostic stage-1.
- arch-specific relocation type codes are mapped directly as macros
rather than via an inline translation function/switch statement.
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the main motivation for this change is to aid in debugging. since the
main program's entry point is also named _start, it was difficult to
set breakpoints or quickly identify which _start execution stopped in.
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two actual issues: one is that __dynlink no longer wants/needs a GOT
pointer argument, so the code to generate that argument can be
removed. the other issue was that in the i386 code, argc/argv were
being loaded into registers that would be call-clobbered, then copied
to preserved registers, rather than just being loaded into the proper
call-preserved registers to begin with.
this cleanup is in preparation for adding new dynamic linker
functionality (ability to explicitly invoke the dynamic linker to run
a program).
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leaving it uninitialized caused unpredictable crashes or worse due to
calling an indeterminate function pointer.
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some notes:
- library search path is hard coded
- x86_64 code is untested and may not work
- dlopen/dlsym is not yet implemented
- relocations in read-only memory won't work
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