On 06.08.21 15:34, Philippe Gerum wrote: > > Jan Kiszka <jan.kis...@siemens.com> writes: > >> On 06.08.21 15:09, Philippe Gerum wrote: >>> >>> Jan Kiszka <jan.kis...@siemens.com> writes: >>> >>>> Hi all, >>>> >>>> just wanted to debug the RTnet issues we now see in CI on arm and arm64. >>>> I picked arm as first target, but that apparently starts to break with >>>> gcc-9 or newer (tried 9.2 and 10.2): >>>> >>>> make[5]: Entering directory '/xenomai/lib/cobalt/arch/arm' >>>> CC libarch_la-features.lo >>>> features.c: In function 'cobalt_arch_check_features': >>>> features.c:82:1: error: r7 cannot be used in 'asm' here >>>> 82 | } >>>> | ^ >>>> >>>> That seems to be related to passing the syscall number via r7 on ARM. Is >>>> our ABI soon no longer compilable, or can we fix this? >>>> >>>> Jan >>> >>> r7 may be used as a scratch register by gcc in some >>> cases. -fomit-frame-pointer for debug builds may help (i.e. when the >>> optimizer is switched off). >>> >> >> Good hint. I had --enable-debug=full set, and it builds without it (and >> now reports other issues that Debian's gcc-10 sees). >> >> But how to resolve this properly? >> >> Jan > > XENOMAI_SYSCALL2(sc_cobalt_archcall) in features.c is likely the issue. > > Either move those bits into some new syscall wrapper which would live in > lib/cobalt/internal.c, where there is no register allocation conflict so > far. Or discourage gcc from using r7 as a scratch register in > arm/features.c entirely? e.g.: > > diff --git a/lib/cobalt/arch/arm/Makefile.am b/lib/cobalt/arch/arm/Makefile.am > index a5095be3d..d5e542ebe 100644 > --- a/lib/cobalt/arch/arm/Makefile.am > +++ b/lib/cobalt/arch/arm/Makefile.am > @@ -6,6 +6,7 @@ libarch_la_SOURCES = features.c > > libarch_la_CPPFLAGS = \ > @XENO_COBALT_CFLAGS@ \ > + -fomit-frame-pointer \ > -I$(srcdir)/../.. \ > -I$(top_srcdir)/include/cobalt \ > -I$(top_srcdir)/include >
-fomit-frame-pointer does not help with -O0. It even keeps the problem alive with -O2. Looks like arm needs a non-unlined helper function for syscalls, to be safe. Jan -- Siemens AG, T RDA IOT Corporate Competence Center Embedded Linux
