Specifications

Related Information
• Porting to GCC 4.7
For more information about how GNU also provides a porting guide to GCC4.7 to document
common issues.
• GCC Releases
For more information about full GCC release notes.
Nios II Specific Changes
• Use __buildin_custom_* instead of -mcustom-* or #pragma to reliably generate Nios II Floating
Point Custom Instructions (FPCI), independent of compiler optimization level and command line
flags.
• To use -mcustom-* or #pragma for Nios II Floating Point Custom Instructions (FPCI):
• The -ffinite-math-only flag must be used to generate fmins and fmax FPCI
• The optimization (non -O0 flag) must be used to generate fsqrts FPCI
• Users implementing transcendental functions in hardware must use the -funsafe-math-optimiza-
tions flag to generate the FPCI for the transcendental functions fsins(), fcoss(), ftans(),
fatans(), fexps(), flogs() and corresponding double-precision functions.
• The Pragma format has changed from eg. #pragma custom_fadds 253 to #pragma GCC
target("custom-fadds=253") and function attributes provide an alternative format
__attribute__((target("custom-fadds=253"))).
• Use the -mel/-meb flags instead of -EL/-EB for endian settings. Software Build Tool for Eclipse
(SBTE) users must regenerate the BSP for this setting to take effect.
• The -mreverse-bitfields flag and reverse_bitfields pragma are no longer supported.
• The -fstack-check flag must be used instead of -mstack-check to enable stack checking.
GCC Changes and Enhancements
• The -Wa,-relax-all flag in nios2-elf-gcc GCC 4.7.3 supports function calls and programs
exceeding the 256 MB limit.
• When used with optimization, inline assembly code with the asm operator needs to declare values
imported from C and exported back to C, using the mechanisms described on the "Exteded Asm -
Assembler Instructions with C Expression Operands" page.
• Pre-standard C++ headers are not supported in GCC 4.7.3. Replace pre-standard C++ with standard C
++ eg. #include <iostream.h>, cout, endl with #include <iostream>, std::cout and
std::endl, respectively.
• The compile flag -Wl,--defsym foo=bar where bar is an undefined symbol, will generate error at the
linker level in GCC 4.7.3. GCC 4.1.2 does not include this check.
Related Information
• Nios II Software Build Tools on page 4-1
For more information about the GCC toolchains.
• Getting Started from the Command Line on page 3-1
• Extended Asm - Assembler Instructions with C Expression Operands
• Altera Software Installation and Licensing Manual
For more information about installing the Altera Complete Design Suite.
NII5V2
2015.05.14
Nios II Specific Changes
2-35
Getting Started with the Graphical User Interface
Altera Corporation
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