loader: Provide memset, and use weak linkage instead of symbol renaming.

[maleadt]

This ensures that the compiler may generate calls to these functions. Fixes #51680

Also, since we're using -ffreestanding for non-Windows platforms too, shouldn't the definitions of memset etc be put in loader_lib.c?

julia/cli/Makefile

Lines 10 to 11 in e949236

	LOADER_CFLAGS = $(JCFLAGS) -I$(BUILDROOT)/src -I$(JULIAHOME)/src -I$(JULIAHOME)/src/support -I$(build_includedir) -ffreestanding
	LOADER_LDFLAGS = $(JLDFLAGS) -ffreestanding -L$(build_shlibdir) -L$(build_libdir)

GCC requires the freestanding environment provide memcpy, memmove, memset and memcmp

cc @gbaraldi

[gbaraldi]

Apparently we get them from libgcc on other platforms.

[staticfloat]

I think this is an innovative solution, but I'd like @vtjnash to rubber-stamp this. My only concern is that we will need to follow the function signature of the "real" functions quite closely to avoid difficult-to-debug errors.

[vtjnash]

IIRC, weak will interact very badly with loading shared libraries later. I think you just want JL_HIDDEN here?

[gbaraldi]

Though will the compiler find that?

[maleadt]

__attribute__((hidden)) is not available on Windows, and JL_HIDDEN is a no-op:

julia/cli/loader.h

Lines 55 to 61 in 8a847d5

	#ifdef _OS_WINDOWS_
	# ifdef JL_LIBRARY_EXPORTS
	# define JL_DLLEXPORT __declspec(dllexport)
	# endif
	# define JL_DLLIMPORT __declspec(dllimport)
	#define JL_HIDDEN
	#else

Or is that what you mean, i.e., that the default visibility would work fine for this?

[vtjnash]

Default visibility is fine. It is what we do for the other interceptors too (eg float16 ABI correction)

[gbaraldi]

Won't this override memcpy for the whole process though?

[vtjnash]

No, the windows linker is (fortunately) incapable of causing such chaos