relocations

Relocations.
------------

Xtensa uses RELA relocations:

typedef struct {
	Elf32_Addr r_offset;
	uint32_t   r_info;
	int32_t    r_addend;
} Elf32_Rela;

r_offset  This member gives the location at which to apply the
	  relocation action. For a relocatable file, the value is
	  the byte offset from the beginning of the section to the
	  storage unit affected by the relocation. For an executable
	  file or shared object, the value is the virtual address of
	  the storage unit affected by the relocation.

r_info    This member gives both the symbol table index with respect
	  to which the relocation must be made and the type of
	  relocation to apply. Relocation types are processor-
	  specific. When the text refers to a relocation entry's
	  relocation type or symbol table index, it means the result
	  of applying ELF32_R_TYPE (LSB) or ELF32_R_SYM (3 MSB),
	  respectively, to the entry's r_info member.

r_addend  This member specifies a constant addend used to compute the
	  value to be stored into the relocatable field.


Xtensa TLS descriptor structures:

typedef struct dl_tls_index
{
	unsigned long int ti_module;
	unsigned long int ti_offset;
} tls_index;

ti_module  Internal index of the module containing TLS variable used by
	   the dynamic linker. This index is used to access DTV array.

ti_offset  Offset of the variable inside module's TLS area.

struct tlsdesc_dynamic_arg
{
	tls_index tlsinfo;
	size_t gen_count;
};


Relocation calculation symbols:

A	Addend encoded in the relocation.
S	Address of a symbol referred to by relocation.
T	Module's offset in the static TLS block.
v	Value at location being relocated.


Xtensa relocation types:

Name:		R_XTENSA_NONE
Meaning:	Placeholder, no actual relocation.
Generated by:	Linker.
Reloc type:	N/A
ELF types:	REL, DYN, EXEC
Sections:	.rela.*
Calculation:	N/A


Name:		R_XTENSA_32
Meaning:	Reference to a symbol.
		For local symbols, symbol referred to is of the section that
		contains target symbol.
		It turns into R_XTENSA_GLOB_DAT in DYN and EXEC when linked
		against dynamic symbol.
		It turns into R_XTENSA_RELATIVE when linked statically.
Generated by:	Assembler.
Reloc type:	Partial in place.
		Both the value of the field being relocated and addend may be
		non-zero. For historical reasons, BFD mention issues with
		DWARF after partial linking.
ELF types:	REL
Sections:	.rela.<referenced section name>
Calculation:	S + A + v


Name:		R_XTENSA_RTLD
Meaning:	Special relocations for runtime linker. Runtime linker replaces
		data pointed to by relocation with r_addend == 1 with a pointer
		to runtime linker dynamic resolver function, and data pointed
		to by relocation with r_addend == 2 with a pointer to the link
		map for the shared object. R_XTENSA_RTLD point to two words at
		the beginning of each .got.plt chunk. PLT entry code calls
		runtime linker dynamic resolver function with two arguments:
		pointer to the link map for the shared object and relocation
		index.
Generated by:	Linker.
Reloc type:	Custom.
ELF types:	DYN, EXEC
Sections:	.rela.dyn
Calculation:	Filled in by dynamic linker.


Name:		R_XTENSA_GLOB_DAT
Meaning:	Reference to a dynamic symbol.
Generated by:	Linker.
Reloc type:	True RELA.
ELF types:	DYN, EXEC
Sections:	.rela.dyn
Calculation:	S + A


Name:		R_XTENSA_JMP_SLOT
Meaning:	Reference to a dynamic function-type symbol.
Generated by:	Linker.
Reloc type:	True RELA.
ELF types:	DYN, EXEC
Sections:	.rela.plt
Calculation:	S + A


Name:		R_XTENSA_RELATIVE
Meaning:	Reference to a location in the same object.
Generated by:	Linker.
Reloc type:	Partial in place, not marked as such in BFD.
ELF types:	DYN, EXEC
Sections:	.rela.dyn
Calculation:	v


Name:		R_XTENSA_PLT
Meaning:	Reference to a symbol, for which the linker will have to
		create PLT entry.
		It turns into R_XTENSA_JMP_SLOT in .rela.plt in DYN and EXEC.
Generated by:	Assembler. @plt suffix.
Reloc type:	True RELA.
ELF types:	REL
Sections:	.rela.<referenced section name>
Calculation:	S + A


Name:		R_XTENSA_OP{0..2}
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_ASM_EXPAND
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_ASM_SIMPLIFY
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_32_PCREL
Meaning:	PC-relative reference to a local symbol. May not be used with
		code, only with data. Gets resolved and disappears completely
		after final linking.
		Used to prepare data for exception handling code.
Generated by:	Assembler. @pcrel suffix.
Reloc type:	True RELA.
ELF types:	REL
Sections:	.rela.<referenced section name>
Calculation:	S + A - PC


Name:		R_XTENSA_GNU_VTINHERIT
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_GNU_VTENTRY
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_DIFF8
Name:		R_XTENSA_DIFF16
Name:		R_XTENSA_DIFF32
Meaning:	1-, 2- or 4-byte signed difference between two defined
		locations in the same section. Only kept for relaxation, may
		be ignored when relaxation is not performed.
Generated by:	Assembler.
Reloc type:	This relocation type is deprecated because its semantic is
		inconsistent: it cannot support both unsigned and signed 8-
		and 16-bit values, resulting in linking errors. It is no
		longer generated by assembler, but still supported by linker
		with the existing semantic.
		Partial in place, not marked as such in BFD.
		The value of the field being relocated is the current
		difference. S + A points to the subtrahend. If minuend is a
		global symbol S points to it, otherwise it points to the
		containing section.
ELF types:	REL
Sections:	.rela.<referenced section name>
Calculation:	v(relaxed) = (S + A + v(sign extended))(relaxed) - (S + A)(relaxed)


Name:		R_XTENSA_SLOT{0..14}_OP
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_SLOT{0..14}_ALT
Meaning:
ELF types:
Calculation:


Name:		R_XTENSA_TLSDESC_FN
Meaning:	Reference to a __tls_get_addr-like function. Function is
		chosen by the dynamic linker depending on whether the space for
		module's TLS variables was allocated statically or dynamically.
Generated by:	Assembler. @tlsfunc suffix mentioned in movi relaxed to l32r.
Reloc type:	Custom.
ELF types:	REL, DYN, EXEC
Sections:	.rela.<referenced section name>, .rela.dyn
Calculation:	Filled in by dynamic linker.


Name:		R_XTENSA_TLSDESC_ARG
Meaning:	Reference to a __tls_get_addr-like function argument. The
		argument may be a TLS variable descriptor pointer or an offset
		inside the static TLS allocation. Dynamic linker has to make
		it match the type of the __tls_get_addr-like function in the
		corresponding R_XTENSA_TLSDESC_FN relocation.
		See Xtensa TLS descriptor structures above.
Generated by:	Assembler. @tlsarg suffix mentioned in movi relaxed to l32r.
Reloc type:	True RELA.
ELF types:	REL, DYN, EXEC
Sections:	.rela.<referenced section name>, .rela.dyn
Calculation:	S + A or S + A + T


Name:		R_XTENSA_TLS_DTPOFF
Meaning:	TLS variable offset relative to its module's TLS variable
		block. It either disappears when linking into DYN, or turns
		into R_XTENSA_TLS_TPOFF when linking into EXEC.
Generated by:	Assembler. @dtpoff suffix mentioned in movi relaxed to l32r.
ELF types:	REL
Calculation:


Name:		R_XTENSA_TLS_TPOFF
Meaning:	TLS variable offset relative to the TLS pointer.
Generated by:	Assembler or linker. @tpoff suffix mentioned in movi relaxed
		to l32r.
Reloc type:	True RELA.
ELF types:	REL, EXEC
Sections:	.rela.<referenced section name>, .rela.dyn
Calculation:	S + A + T


Name:		R_XTENSA_TLS_FUNC
Meaning:	Opcode loading __tls_get_addr-like function address into
		register.
		It is used for link-time relaxation only.
Generated by:	Assembler. @tlsfunc suffix mentioned in movi relaxed to l32r.
ELF types:	REL
Calculation:


Name:		R_XTENSA_TLS_ARG
Meaning:	Opcode loading __tls_get_addr-like function parameter (TLS
		variable index pointer) into register.
		It is used for link-time relaxation only.
Generated by:	Assembler. @tlsarg suffix mentioned in movi relaxed to l32r.
ELF types:	REL
Calculation:


Name:		R_XTENSA_TLS_CALL
Meaning:	__tls_get_addr-like function call.
		It is used for link-time relaxation only.
Generated by:	Assembler. @tlscall suffix to additional call*.tls argument.
ELF types:	REL
Calculation:


Name:		R_XTENSA_PDIFF8
Name:		R_XTENSA_PDIFF16
Name:		R_XTENSA_PDIFF32
Meaning:	1-, 2- or 4-byte unsigned positive difference between two
		defined locations in the same section. Only kept for
		relaxation, may be ignored when relaxation is not performed.
Generated by:	Assembler.
Reloc type:	Partial in place, not marked as such in BFD.
		The value of the field being relocated is the current
		difference. S + A points to the subtrahend. If minuend is a
		global symbol S points to it, otherwise it points to the
		containing section.
ELF types:	REL
Sections:	.rela.<referenced section name>
Calculation:	v(relaxed) = (S + A + v(zero extended))(relaxed) - (S + A)(relaxed)


Name:		R_XTENSA_NDIFF8
Name:		R_XTENSA_NDIFF16
Name:		R_XTENSA_NDIFF32
Meaning:	1-, 2- or 4-byte unsigned negative difference between two
		defined locations in the same section. Only kept for
		relaxation, may be ignored when relaxation is not performed.
Generated by:	Assembler.
Reloc type:	Partial in place, not marked as such in BFD.
		The value of the field being relocated is the current
		difference. S + A points to the subtrahend. If minuend is a
		global symbol S points to it, otherwise it points to the
		containing section.
ELF types:	REL
Sections:	.rela.<referenced section name>
Calculation:	v(relaxed) = (S + A + v(one extended))(relaxed) - (S + A)(relaxed)