33 Document Revision History

Revision A (August 2018)

Initial revision of the document.

Revision B (April 2020)

The document was re-formatted throughout, including paragraph numbering and minor editing changes.
Added new topic How Do I Stop My Project's Checksum From Changing? to the How To’s section.
Corrected description of option -fenforce-eh-specs in Table 4-7.
Revised Command-line Driver section extensively.
Updated Case 3 and Case 4 in Using an Application-Defined Memory Region.
Added examples for keep and noload in the Function Attributes and Specifiers.
Adding more information to Jump to NMI Handler (_nmi_handler) if an NMI Occurred.

Revision C (May 2023)

Updated the stated size and information relating to the double type, which is now 64 bits wide.
Corrected examples of using the __pack specifier.
Updated information on the compiler option controls available in the MPLAB X IDE.
Provided dedicated sections on all compiler options in addition to a summary table.
Added new section on the compiler's code coverage feature.
Added a new section on the stack and the stack guidance feature.
Added -f[no-]common option description, which controls the placement of global variables defined without an initializer.
Added -Warray-bounds option description, which can warn on out-of-bounds array indices and pointer offsets.
Added -Wmultistatement-macros option description, which warns on unsafe macro expansion.
Added -Wsizeof-pointer-div option description, which warns on suspicious divisions involving pointers.
Indicated that the -foptimize-register-move option no longer has any effect.
Added information on the iar argument to the -mext option.
Added information on the used variable attribute.
Added information on the externally_visible function attribute and variable attribute.
Expanded information on the naked function attribute.
Updated and expanded the sections relating to variables in program memory, reflecting changes in the compiler.
Expanded information on fixed-point types and arithmetic.
Expanded information on interrupt context switching.
Updated information on the runtime startup code, including information on the data initialization template.
Added information on smart IO library features.
Expanded information on optimizations performed.
Added section on preprocessor arithmetic.
Added information on the default_function_attributes, default_variable_attributes, message, GCC optimize, pack, and weak pragmas.
Removed reference to the __PIC__ and __pic__ position independent code macros, which are no longer supported.
Indicated in the default linker script information that selecting an alternate DFP will affect the script used.
Added information on __builtin_mfc0 and __builtin_mtc0 built-in functions.
Corrected information relating to the return value for the __builtin_bcc0, __builtin_bsc0, and __builtin_bcsc0 built-in functions.

Revision D (September 2023)

Merged the MIPS-related library content in the 32-Bit Language Tools Libraries document into this guide.
Updated references to the C++ standard to reflect that the ISO/IEC 14882:2014 C++ program language is now supported.
Renamed references to the MPLAB XC16 compiler to be MPLAB XC-DSC to reflect the change in product name.
Defined the compiler's implementation-defined behavior for the C++14 standard in a new section.
Clarified information in the runtime startup section.
Updated Common C Interface chapter to reflect recent changes in MPLAB XC compilers.
Removed reference to MPLAB XC8 in the Embedded Compiler Compatibility Mode chapter, as this compiler no longer supports this mode.

Revision E (June 2024)

Added new How To explaining how the stack usage for each function in a module can be displayed
Updated compiler options used with the Linktime Optimizations setting in XC32 Global options tab of the MPLAB X IDE Project Properties
Added option present in the xc32-ar (Library Archive) tab of the MPLAB X IDE Project Properties
Added a diagram indicating the internal compiler applications
Updated information relating to runtime startup files

Added the following option descriptions to the guide:


`-mmalloc-variant`	`-mips16e`	`--version`
`-mlibc-variant`	`-std`	`-Wformat-smart-io`
`-dA`	`-fdiagnostics-show-caret`	`-fframe-base-loclist`
`-mno-info-linker`	`-ffat-lto-objects`	`-finline-small-functions`
`-flto-partition`	`-fpeel-loops`	`-ftracer`
`-fuse-linker-plugin`	`-T`

Corrected typo in the name of what should have been the --dint-compression option and specified this with the -Wl, prefix, since it is a linker option
Updated the Dynamic Memory Allocation section to include the new allocation schemes
Updated several items in the Common C Interface section to improve readability and include the XC-DSC compiler
Expanded the description of the __builtin_disable_interrupts and __builtin_enable_interrupts Built-in Functions

Revision F (June 2025)

Modified compiler command-line examples to now use the -mdfp option
Update dreferenced compiler installation paths from pic32mx to pic32m
Updated the paths where the runtime startup code files can be found after extraction from the shipped archive file
Indicated that improved object file compatibility might mean that some Microchip-specific features may not work with third party tools_p
Added more information to the -mdfp option regarding the use of DFPs
Indicated in the descriptions of the -o and -save-temps options that they additionally control the name and location of aux and dump files
Added new options: -Warray-compare, -Warray-parameter, -Wenum-int-mismatch, -Wmismatched-dealloc, -Wmismatched-new-delete, -Wself-move, -Wsizeof-array-div, -Wvla-parameter, -Wzero-length-bounds, -Wabsolute-value, -Waddress-of-packed-member, -Wbidi-chars, -Wc++11-extensions, -Wc++14-extensions, -Wc++17-extensions, -Wc++20-extensions, -Wc++23-extensions, -Wctad-maybe-unsupported, -Wdangling-reference, -Wdeprecated-enum-enum-conversion, -Wdeprecated-enum-float-conversion, -Wmissing-requires,-Wrange-loop-construct, -Wstring-compare, -Wstringop-overread, -Wvexing-parse, and -Wxor-used-as-pow
Adjusted the default setting for the feature controlled by -fcommon, which has recently changed in the compiler
Removed the section for -aux-info, as this option is not fully supported
Corrected information in the -D and -U preprocessor macro option sections relating to when this option is processed
Corrected the name give to sections used to hold objects or functions that use the address attribute
Added description of the -msemihost option
Added description of the -finline option
Added description of the -ftree-vrp option
Added description of the -nostdlib++ option
Clarified that objects and library archives built with LTO enabled are platform dependent
Corrected typo in -fcall-used-reg option description
Removed floating-point macro definitions that are now documented in the Microchip Unified Standard Library Reference Guide
Removed information on the default_function_attributes and default_variable_attributes, which had been incorrectly added
Indicated that section names associated with persistent objects can vary if other attributes are used with the object
Indicated that section names associated with absolute objects and function have arbitrary names
Added description of new __has_builtin operator
Added description of new access attribute
Added description of new __builtin_has_attribute built-in function
Added descriptions for new __builtin_bswap16, __builtin_bswap32, and __builtin_bswap64 built-in functions
Provided more examples of function attributes
Clarified that care must be taken when using inline assembly code that defines labels
Included xc32-objdump command to generate an assembly listing in the How Do I Know What Code the Compiler Is Producing? How To
Clarified the difference between Free and PRO compilers in the What's the Difference Between a Free and PRO Compiler? How To.

Revision G (December 2025)

Added information relating to the new Picolibc library, an alternative to MUSL, selectable using the --mchp-stdlibc option
Updated the -mreserve option to more accurately describe its use with XC32 compilers
Added a section for the copy variable and function attributes, which have been recently added to the compiler
Added description of the uninitialized and variable attribute
Added sections for the alias function and variable attributes
Added sections for the -fzero-call-used-regs and -ftrivial-auto-var-init options, which are new to the compiler
Added descriptions of the -Wextra option and expanded the description of the -Werror option
Added descriptions of the -Wtrivial-auto-var-init, -Wuninitialized, and -Wno-analyzer-use-of-uninitialized-value warning options
Added information relating to the new word-oriented data initialization feature and associated --mchp-dinit option
Added descriptions of graphical controls for the compiler options available when using the MPLAB Extensions for VS Code
Removed ye olde ASCII table

Revision H (April 2026)

Removed PRO licensing information relating to activation and use of some optimizations
Added new section relating to the thread-local storage (TLS) memory management feature, relevant for programs using threads
Added description of new __thread object qualifier
Added information relating to the picolibc library, with support for thread-local storage
Reworded information relating to ECC memory and the runtime startup sequence