9.116 __ldrexd intrinsic

The __ldrexd intrinsic lets you load doubleword data from memory in your C or C++ code using an LDREXD instruction.


The compiler does not guarantee to preserve the state of the exclusive monitor. It might generate load and store instructions between the LDREXD instruction generated for the __ldrexd intrinsic and the STREXD instruction generated for the __strexd intrinsic. Because memory accesses can clear the exclusive monitor, code using the __ldrexd and __strexd intrinsics can have unexpected behavior. Where LDREXD and STREXD instructions are needed, ARM recommends using embedded assembly.


unsigned long long __ldrexd(volatile void *ptr)
points to the address of the data to be loaded from memory. To specify the type of the data to be loaded, cast the parameter to an appropriate pointer type.

Table 9-9 Access widths that the __ldrex intrinsic supports

Instruction Size of data loaded Pointer type
LDREXD long long long long *

Return value

The __ldrexd intrinsic returns the data loaded from the memory address pointed to by ptr.


The compiler does not recognize the __ldrexd intrinsic when compiling for a target that does not support the LDREXD instruction. The compiler generates either a warning or an error in this case, depending on the source language:
  • In C code: Warning: #223-D: function "__ldrexd" declared implicitly.
  • In C++ code: Error: #20: identifier "__ldrexd" is undefined.
The __ldrexd intrinsic only supports access to doubleword data. The compiler generates an error if you specify an access width that is not supported.
Related reference
9.115 __ldrex intrinsic
9.136 __strex intrinsic
9.137 __strexd intrinsic
Related information
Non-ConfidentialPDF file icon PDF versionARM DUI0375F
Copyright © 2007, 2008, 2011, 2012, 2014 ARM. All rights reserved.