RISC-V eXpress Software Development Manual
- Standard Library Porting -

Kyuseung Han, Sukho Lee, Jae-Jin Lee
ETRI, Daejeon, South Korea

v2025-07-10 or later

Simple Replacement of Headers

Availability of standard libraries

stddef.h stdint.h stdio.h stdlib.h

O O X X

stddef.h	stdint.h	stdio.h	stdlib.h
O	O	X	X

Available variables and functions

Variable/Function	Original Header	Modified Header
u?intXX_t	stdint.h	-
size_t	stddef.h	-
NULL	stddef.h	-
assert	assert.h	ervp_assert.h
EOF	stdio.h	ervp_fakefile.h
printf	stdio.h	ervp_printf.h
malloc	stdlib.h	ervp_malloc.h
calloc	stdlib.h	ervp_malloc.h
free	stdlib.h	ervp_malloc.h
realloc	stdlib.h	ervp_malloc.h
atoi	stdlib.h	ervp_stdlib.h
atof	stdlib.h	ervp_stdlib.h

When replacing header files:
- You do not need to change how the functions are used in the code.
- Original functions are redefined using macros and automatically mapped to the provided alternatives.
- The replacement function names follow the format: #(original function)_rvx.
- Therefore, the original functions must not be included in the compiled ELF file.

File I/O Porting

Overview

Standard file I/O is not supported in RVX. Instead, RVX provides a feature called fakefile to simplify porting.
Fakefile is not a general-purpose file I/O mechanism. Instead, it converts input files into header files that can be accessed through the provided functions.
Because this method relies on compile-time file conversion, only predefined files can be used.
It is suitable for data sizes under a few megabytes. For larger files, RVX is not appropriate due to limitations in functionality and performance.
Output files are stored in the SoC’s main memory and can be retrieved to a PC using the ocd program.
The fakefile feature is supported only on hardware implementations such as FPGA prototypes and is not available in RTL simulation.

Converting Input Files to Headers

cmd) cd #(platform dir)
cmd) make user
cmd) make util
cmd) cd #(platform dir)/util
cmd) make fakefile
cmd) cd #(platform dir)/util/fakefile
cmd) mkdir target
inst) Copy the input files into the ‘target’ directory.
cmd) make all

Modifying C Code

Original		Modified
Variable/Function	Header	Variable/Function	Header
SEEK_SET	stdio.h	-	ervp_fakefile.h
SEEK_CUR	stdio.h	-	ervp_fakefile.h
SEEK_END	stdio.h	-	ervp_fakefile.h
FILE	stdio.h	FAKEFILE	ervp_fakefile.h
fopen	stdio.h	ffopen	ervp_fakefile.h
fputc	stdio.h	ffputc	ervp_fakefile.h
fgetc	stdio.h	ffgetc	ervp_fakefile.h
feof	stdio.h	ffeof	ervp_fakefile.h
fclose	stdio.h	ffclose	ervp_fakefile.h
fgetline	stdio.h	ffgetline	ervp_fakefile.h
fread	stdio.h	ffread	ervp_fakefile.h
ftell	stdio.h	fftell	ervp_fakefile.h
fseek	stdio.h	ffseek	ervp_fakefile.h

Setting Up Compilation Environment

cmd) cd #(app dir)
cmd) make rvx_each
inst) Uncomment ‘USE_FAKEFILE=true’ in rvx_each.mh

Retrieving Output Files to a PC

cmd) cd #(imp dir)
cmd) make dump

Simple Replacement of Headers

File I/O Porting

Overview

Converting Input Files to Headers

Modifying C Code

Setting Up Compilation Environment

Retrieving Output Files to a PC

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