Load a register with either a 32-bit immediate value or an address.
NoteThis describes the
LDRpseudo-instruction only, and not the
is an optional condition code.
is an optional instruction width specifier.
is the register to be loaded.
evaluates to a numeric value.
is a PC-relative or external expression of an address in the form of a label plus or minus a numeric value.
When using the
- If the value of
exprcan be loaded with a valid
MVNinstruction, the assembler uses that instruction.
If a valid
MVNinstruction cannot be used, or if the
label_exprsyntax is used, the assembler places the constant in a literal pool and generates a PC-relative
LDRinstruction that reads the constant from the literal pool.
- An address loaded in this way is fixed at link time, so the code is not position-independent.
- The address holding the constant remains valid regardless of where
the linker places the ELF section containing the
The assembler places the value of
label_expr in a literal pool and generates a PC-relative
LDR instruction that loads the value from the literal pool.
label_expr is an external expression,
or is not contained in the current section, the assembler places a linker relocation
directive in the object file. The linker generates the address at link time.
label_expr is either a named or
numeric local label, the assembler places a linker relocation directive in the object file
and generates a symbol for that local label. The address is generated at link time. If the
local label references T32 code, the T32 bit (bit 0) of the address is set.
The offset from the PC to the value in the literal pool must be less than ±4KB (in an A32 or 32-bit T32 encoding) or in the range 0 to +1KB (16-bit T32 encoding). You are responsible for ensuring that there is a literal pool within range.
If the label referenced is in T32 code, the
LDR pseudo-instruction sets the T32 bit (bit 0) of
NoteIn RealView Compilation Tools (RVCT) v2.2, the T32 bit of the address was not set. If you have code that relies on this behavior, use the command line option
--untyped_local_labelsto force the assembler not to set the T32 bit when referencing labels in T32 code.
LDR in T32 code
You can use the
.W width specifier to
LDR to generate a 32-bit instruction in T32 code.
LDR.W always generates a 32-bit instruction, even if the
immediate value could be loaded in a 16-bit
MOV, or there
is a literal pool within reach of a 16-bit PC-relative load.
If the value to be loaded is not known in the first pass of the assembler,
generates a 16-bit instruction in T32 code, even if that results in a 16-bit PC-relative
load for a value that could be generated in a 32-bit
MVN instruction. However, if the value is known in the
first pass, and it can be generated using a 32-bit
MVN instruction, the
MVN instruction is used.
In UAL syntax, the
pseudo-instruction never generates a 16-bit flag-setting
MOV instruction. Use the
assembler command line option to check when a 16-bit instruction could have been used.
You can use the
for generating immediate values or addresses without loading from a literal pool.
LDR r3,=0xff0 ; loads 0xff0 into R3 ; => MOV.W r3,#0xff0 LDR r1,=0xfff ; loads 0xfff into R1 ; => LDR r1,[pc,offset_to_litpool] ; ... ; litpool DCD 0xfff LDR r2,=place ; loads the address of ; place into R2 ; => LDR r2,[pc,offset_to_litpool] ; ... ; litpool DCD place