This is a syscall implementation and (only slightly modified) linker script for use with Newlib on the Sony PlayStation. Newlib is a portable libc/stdlib implementation that doesn't require a Linux or BSD kernel like most libc's, and is complete and standards-compliant unlike a custom libc.

The PlayStation includes a BIOS ROM that has a number of system support functions, which we use to implement device-specific system calls. However, it additionally includes a few libc functions itself that do not interact with peripherals. As such, Newlib can either be used for all libc functions except as necessary to interact with hardware, or Newlib can be patched to use BIOS routines whereever possible. The second option may run slower in some cases but will result in a smaller executable. Patching newlib is also required if you set any exception handlers, link with the legacy PsyQ libraries (which set exception handlers), or debug with the pcsx-redux emulator.

Option 1: Using a pre-patched, pre-compiled Newlib

Download a pre-compiled bundle from the releases page and install it into your existing MIPSEL prefix. Make sure to use -nodefaultlibs -Tpsx.ld in the linker flags, or if using another linker script, add -lpsxsys manually.

Option 2: Using plain Newlib

1. Copy psx.c and psx.ld to libgloss/mips/.

2. Add them to libgloss/mips/Makefile.in, for example with:

    PSXOBJS = psx.o syscalls.o getpid.o kill.o putnum.o
    libpsxsys.a: $(PSXOBJS)
        ${AR} ${ARFLAGS} $@ $(PSXOBJS)
        ${RANLIB} $@
   

Then continue with "Configuring and compiling Newlib" below.

Option 3: Patching Newlib

1. Copy psx.c, psx.ld, psx-bonus.c, and psx-printf.S to libgloss/mips/.
2. In the top-level Newlib source, run patch -p1 <psx.patch (using the full path of psx.patch).

Then continue with "Configuring and compiling Newlib" below.

Configuring and compiling Newlib

1. Configure Newlib with these flags:
   • --target=mipsel-elf: Required for the platform. The mipsel-unknown-elf triple is sometimes recommended in other tutorials, but it does the same thing.
   • CFLAGS (or CFLAGS_FOR_TARGET for a unified build) set to:
     • -DHAVE_BLKSIZE: Required. PSX file I/O can only be done in block units, so this tells Newlib to enable "optimizations" that transform FS calls to block alignment.
     • -g -O2: From the default configuration.
     • -DHAVE_RENAME: Not required, but you'll need to remove _rename from psx.c if you don't add the flag.
   • --prefix=/usr/local/psxsdk or whatever. Optional but recommended to keep your host system root clean.
   • --disable-multilib: Optional, but recommended to keep the prefix clean. Disables building extra, unnecessary big-endian and hard-float versions of target libraries.
   • --enable-lto: Optional but recommended. Enables link-time-optimization, building intermediate code so that optimizations can be performed all at once during linking.
   • --disable-libssp: Optional. Disables support for stack protection.
   • --disable-libstdcxx: Optional. Disables support for GNU libstdc++-v3.
   • --disable-newlib-hw-fp: Optional. Enforces disabling hard-float support.
   • --disable-newlib-io-float: Optional. Disables floating point in format strings.
   • --disable-newlib-multithread: Optional. Disables threading support.
   • --disable-shared: Optional. Do not build shared libraries.
   • --enable-lite-exit: Optional. Console games don't typically exit, so why spend time there?
   • --enable-newlib-nano-malloc: Optional. Enables an alternative malloc implementation, "which is for small systems with very limited memory."

For example, here's my full configure line, using a "unified" build alongside binutils and GCC:

../configure --prefix=/usr/local/psxsdk --target=mipsel-elf \
    --disable-gcov \
    --disable-libssp \
    --disable-libstdcxx \
    --disable-multilib \
    --disable-newlib-hw-fp \
    --disable-newlib-io-float \
    --disable-newlib-multithread \
    --disable-nls \
    --disable-shared \
    --enable-gold \
    --enable-languages=c,c++ \
    --enable-lite-exit \
    --enable-lto \
    --enable-serial-configure \
    --with-float=soft \
    --with-isl \
    --with-newlib \
    --with-no-pic \
    CFLAGS_FOR_TARGET="-g -O2 -DHAVE_BLKSIZE -DHAVE_RENAME"

Then make and make install as usual. Add the new prefix to your PATH if necessary, then you can use mipsel-elf-gcc with -flto -msoft-float -march=r3000 to build things, and mipsel-elf-gcc-ld with -nodefaultlibs -Tpsx.ld to link things.

Platform support

Stubbed OS subroutines (meaningless on the system, but do not return error)

• environ
• getpid
• kill

Library functions affected by stubbed OS subroutines (may not behave as expected)

• assert
• getenv, _getenv_r
• raise, _raise_r
• tmpfile, tmpfile_r
• tmpfile64, _tmpfile64_r
• tmpnam, tempnam, _tmpnam_r, _tempnam_r

Unsupported OS subroutines (always return error)

• gettimeofday
• link

Library functions affected by unsupported OS subroutines (always return error)

• _gettimeofday_r
• _link_r
• time

Unimplemented OS subroutines (programs that use these will fail to link)

• dup2
• execve
• execvpe
• fcntl
• fork
• fstat64
• lseek64
• mkdir
• open64
• pipe
• sched_setparam
• sched_setscheduler
• setegid
• seteuid
• setpgid
• sigaction
• sigprocmask
• symlink
• times
• vfork
• wait
• waitpid

Library functions affected by unimplemented OS subroutines (programs that use these will fail to link)

• _execve_r
• _fcntl_r
• _fork_r
• _fstat64_r
• _lseek64_r
• _mkdir_r
• _open64_r
• _times_r
• _wait_r
• clock
• fopen64, _fopen64_r
• freopen64, _freopen64_r
• fseeko64, _fsseko64_r
• fsetpos64, _fsetpos64_r
• mktemp, mkdtemp, mkstemp, mkstemps, mkostemp, mkostemps, _mktemp_r, _mkdtemp_r, _mkstemp_r, _mkstemps_r, _mkostemp_r, _mkostemps_r
• popen, pclose
• posix_spawn, posix_spawnp
• pread64
• pwrite64
• system, _system_r
• tmpfile64, _tmpfile64_r

To do

• Make a custom, slimmer crt0.s. The built-in one is great, but 1) supplies _exit, which could be done as a syscall, and 2) zeroes .bss and does some other system initialization that the BIOS boot sequence already does.
• Pass argv to main. Syscall A(0x43) passes parameters to r4 and r5, presumably argc and argv (though they are 0 and null for the boot executable)
• The boot executable copies some of system.cnf to 0x180—could this be used for environment?
• Add syscall versions of malloc and memset.
• Consider -O2 vs -Os vs -O3.

Thanks

• Adrian Siekierka for candyk, which helped me figure out some of the configure flags
• Nicolas Noble for Openbios, which helped me figure out how some of the BIOS calls work, and also how to do them inline in C
• Nocash for the PSX Specifications
• NextVolume and Lameguy64 for their existing PS1 SDKs