Re: [PATCH v3 2/2] tools/nolibc: add support for 32-bit parisc

[Thomas Weißschuh]

On 2026-04-09 00:15:54+0200, Helge Deller wrote:
> * Thomas Weißschuh <linux@xxxxxxxxxxxxxx>:
> > Extend nolibc to target the 32-bit parisc architecture.
> > 64-bit is not yet supported.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
> > ---
> >  tools/include/nolibc/Makefile                  |   2 +-
> >  tools/include/nolibc/arch-parisc.h             | 178 +++++++++++++++++++++++++
> >  tools/include/nolibc/arch.h                    |   2 +
> >  tools/testing/selftests/nolibc/Makefile.nolibc |   6 +
> >  tools/testing/selftests/nolibc/run-tests.sh    |   8 +-
> >  5 files changed, 194 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile
> > index 7455097cff69..81187126bf93 100644
> > --- a/tools/include/nolibc/Makefile
> > +++ b/tools/include/nolibc/Makefile
> > @@ -17,7 +17,7 @@ endif
> >  # it defaults to this nolibc directory.
> >  OUTPUT ?= $(CURDIR)/
> >  
> > -architectures := arm arm64 loongarch m68k mips powerpc riscv s390 sh sparc x86
> > +architectures := arm arm64 loongarch m68k mips parisc powerpc riscv s390 sh sparc x86
> >  arch_files := arch.h $(addsuffix .h, $(addprefix arch-, $(architectures)))
> >  all_files := \
> >  		byteswap.h \
> > diff --git a/tools/include/nolibc/arch-parisc.h b/tools/include/nolibc/arch-parisc.h
> > new file mode 100644
> > index 000000000000..8580be5c9c58
> > --- /dev/null
> > +++ b/tools/include/nolibc/arch-parisc.h
> > @@ -0,0 +1,178 @@
> > +/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
> > +/*
> > + * parisc/hppa (32-bit) specific definitions for NOLIBC
> > + * Copyright (C) 2026 Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
> > + */
> > +
> > +#ifndef _NOLIBC_ARCH_PARISC_H
> > +#define _NOLIBC_ARCH_PARISC_H
> > +
> > +#if defined(__LP64__)
> > +#error 64-bit not supported
> > +#endif
> > +
> > +#include "compiler.h"
> > +#include "crt.h"
> > +
> > +/* Syscalls for parisc :
> > + *   - syscall number is passed in r20
> > + *   - arguments are in r26 to r21
> > + *   - the system call is performed by calling "ble 0x100(%sr2, %r0)",
> > + *     the instruction after that is executed first, use it to load the number
> better:
>    the instruction after that is in the delay slot and executed before the jump
>    to 0x100 actually happens.

Ack.

> > + *   - syscall return comes in r28
> > + *   - the arguments are cast to long and assigned into the target
> > + *     registers which are then simply passed as registers to the asm code,
> > + *     so that we don't have to experience issues with register constraints.
> 
> side-note:
> this is actually really tricky.
> I've seen cases, where the syscalls were not using the given registers,
> because the callers were too complicated and the compiler could not guarantee
> to actually use the given register.

This is weird. We are using the same pattern for all other
architectures, too and so far that worked fine.
Was it a compiler bug?

(...)

> > +#ifndef NOLIBC_NO_RUNTIME
> > +/* startup code */
> > +void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
> > +{
> > +	__asm__ volatile (
> > +		".import $global$\n"           /* Set up the dp register */
> > +		"ldil L%$global$, %dp\n"
> > +		"ldo R%$global$(%r27), %dp\n"
> > +
> > +		"ldo -4(%r24), %r26\n"         /* The sp register is special on parisc.
> > +						* r24 points to argv. Subtract 4 to get &argc.
> > +						* Pass that as first argument to _start_c.
> > +						*/
> > +
> > +		"b,n _start_c\n"
> 
> you can change that to "b _start_c\" (without ",n") and move it
> one line up before the "ldo -4..." instruction. It's a little bit faster".
> The ldo is then in the delay slot.

Ack.

> > +	);
> > +	__nolibc_entrypoint_epilogue();
> > +}
> > +#endif /* NOLIBC_NO_RUNTIME */

(...)

> >  QEMU_ARCH_USER_ppc64le = ppc64le
> > @@ -199,6 +203,7 @@ QEMU_ARGS_sparc32    = -M SS-5 -m 256M -append "console=ttyS0,115200 panic=-1 $(
> >  QEMU_ARGS_sparc64    = -M sun4u -append "console=ttyS0,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
> >  QEMU_ARGS_m68k       = -M virt -append "console=ttyGF0,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
> >  QEMU_ARGS_sh4        = -M r2d -serial file:/dev/stdout -append "console=ttySC1,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
> > +QEMU_ARGS_parisc32   = -append "console=ttyS0 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
> 
> You could change that to (untested):
> QEMU_ARGS_parisc32   = -M B160L -append "panic=-1 $(TEST:%=NOLIBC_TEST=%)" -nographic

Will try.

> >  QEMU_ARGS            = -m 1G $(QEMU_ARGS_$(XARCH)) $(QEMU_ARGS_BIOS) $(QEMU_ARGS_EXTRA)
> >  
> >  # OUTPUT is only set when run from the main makefile, otherwise
> > @@ -215,6 +220,7 @@ CFLAGS_i386 = $(call cc-option,-m32)
> >  CFLAGS_x32 = -mx32
> >  CFLAGS_arm = -marm
> >  CFLAGS_armthumb = -mthumb -march=armv6t2
> > +CFLAGS_parisc32 = -mfast-indirect-calls
> 
> would be good if we could go without this...
> But for the beginning it's ok.

Why? As nolibc is compiled again for each application, any users which
don't want this don't get it. For nolibc-test it avoids a dependency on
libgcc.


Thomas