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98 lines
3.6 KiB
Makefile
98 lines
3.6 KiB
Makefile
##
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## Create an ABI stub named '<lib>.abi.so'
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##
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## Invoked from the library's build directory within the lib cache.
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## The following variables must be passed when calling this file:
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##
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## BASE_DIR - base directory of the build system
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## VERBOSE - build verboseness modifier
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## LIB_CACHE_DIR - library build cache location
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## LIB - library name
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## SYMBOLS - path of symbols file
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## SPECS - build specs (i.e., CPU architecture)
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##
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#
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# An ABI-stub library does not contain any code or data but only the symbol
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# information of the binary interface (ABI) of the shared library.
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#
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# The ABI stub is linked by the users of the library (executables or shared
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# objects) instead of the real library. This effectively decouples the library
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# users from the concrete library instance but binds them merely to the
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# library's binary interface. Note that the ABI stub is not used at runtime at
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# all. At runtime, the real library that implements the ABI is loaded by the
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# dynamic linker.
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#
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# The symbol information are incorporated into the ABI stub via an assembly
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# file named 'symbols.s' that is generated from the library's symbol list.
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#
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ABI_SO := $(addsuffix .abi.so,$(LIB))
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SYMBOLS := $(wildcard $(SYMBOLS))
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ifeq ($(SYMBOLS),)
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all:
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else
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all: $(ABI_SO)
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endif
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include $(BASE_DIR)/mk/util.inc
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include $(SPEC_FILES)
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include $(BASE_DIR)/mk/global.mk
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include $(BASE_DIR)/mk/generic.mk
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#
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# Generate assembler file from symbol list
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#
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# For undefined symbols (type U), we create a hard dependency by referencing
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# the symbols from the assembly file. The reference is created in the form of
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# a '.long' value with the address of the symbol. On x86_64, this is not
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# possible for PIC code. Hence, we reference the symbol via a PIC-compatible
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# movq instruction instead.
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#
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# If we declared the symbol as '.global' without using it, the undefined symbol
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# gets discarded at link time unless it is directly referenced by the target.
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# This is a problem in situations where the undefined symbol is resolved by an
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# archive rather than the target. I.e., when linking posix.lib.a (which
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# provides 'Libc::Component::construct'), the 'construct' function is merely
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# referenced by the libc.lib.so's 'Component::construct' function. But this
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# reference apparently does not suffice to keep the posix.lib.a's symbol. By
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# adding a hard dependency, we force the linker to resolve the symbol and don't
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# drop posix.lib.a.
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#
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ASM_SYM_DEPENDENCY := .long \1
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ifeq ($(filter-out $(SPECS),x86_64),)
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ASM_SYM_DEPENDENCY := movq \1@GOTPCREL(%rip), %rax
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endif
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symbols.s: $(SYMBOLS)
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$(MSG_CONVERT)$@
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$(VERBOSE)\
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sed -e "s/^\(\w\+\) D \(\w\+\)\$$/.data; .global \1; .type \1,%object; .size \1,\2; \1: .skip 1/" \
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-e "s/^\(\w\+\) V/.data; .weak \1; .type \1,%object; \1: .skip 1/" \
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-e "s/^\(\w\+\) T/.text; .global \1; .type \1,%function; \1:/" \
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-e "s/^\(\w\+\) R \(\w\+\)\$$/.section .rodata; .global \1; .type \1,%object; .size \1,\2; \1:/" \
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-e "s/^\(\w\+\) W/.text; .weak \1; .type \1,%function; \1:/" \
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-e "s/^\(\w\+\) B \(\w\+\)\$$/.bss; .global \1; .type \1,%object; .size \1,\2; \1:/" \
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-e "s/^\(\w\+\) U/.text; .global \1; $(ASM_SYM_DEPENDENCY)/" \
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$< > $@
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#
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# The '.PRECIOUS' special target prevents make to remove the intermediate
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# assembler file. Otherwise make would spill the build log with messages
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# like "rm libc.symbols.s".
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#
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.PRECIOUS: symbols.s
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ABI_SONAME := $(addsuffix .lib.so,$(LIB))
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all: # prevent 'Nothing to be done' message
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@true
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$(ABI_SO): symbols.o
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$(MSG_MERGE)$(ABI_SO)
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$(VERBOSE)$(LD) -o $(ABI_SO) -soname=$(ABI_SONAME) -shared --eh-frame-hdr $(LD_OPT) \
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-T $(LD_SCRIPT_SO) $<
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$(ABI_SO): $(LD_SCRIPT_SO)
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