On Fri, Aug 19, 2011 at 05:38:19PM +0200, Denys Vlasenko wrote: > On Fri, 2011-08-19 at 00:02 +0400, Dmitry V. Levin wrote: [...] > > > --- strace.5/defs.h 2011-08-18 11:57:30.512416447 +0200 > > > +++ strace.6/defs.h 2011-08-18 11:46:56.349540479 +0200 > > > @@ -64,7 +64,7 @@ > > > #define DEFAULT_ACOLUMN 40 /* default alignment column for results > > > */ > > > #endif > > > #ifndef MAX_ARGS > > > -# ifdef HPPA > > > +# if defined HPPA || defined X86_64 || defined I386 > > > # define MAX_ARGS 6 /* maximum number of args to a syscall > > > */ > > > # else > > > /* Way too big. Switch your arch to saner size after you tested that it > > > works */ > > > > What about other architectures? Is there any with MAX_ARGS > 6? > > Can we assume MAX_ARGS == 6 on linux? > > I looked deeper. Apparently FREEBSD needs MAX_ARGS = 8. Also there's > a bug in sys_mmap64 where it will try to access (but not write to) > u_args[6,7] wrongly - see other mail. > > My current knowledge is summed up by this comment: > > /* Maximum number of args to a syscall. > * > * Make sure that all entries in all syscallent.h files > * have nargs <= MAX_ARGS! > * linux/<ARCH>/syscallent.h: ia64 has many syscalls with > * nargs = 8, mips has two with nargs = 7 (both are printargs), > * all others are <= 6. > * freebsd/i386/syscallent.h: one syscall with nargs = 8 > * (sys_sendfile, looks legitimate) > * and one with nargs = 7 (sys_mmap, maybe it should have 6?). > * sunos4/syscallent.h: all are <= 6. > * svr4/syscallent.h: all are -1. > */ > > Basically, all linux arches sans ia64 should be ok with MAX_ARGS = 6.
All linux/ia64/syscallent.h entries with nargs == 8 are printargs. I checked those 3 of them that have meaningful sys_name (other than SYS_*), they definitely take less than 6 arguments. So I suppose ia64 entries with nargs == 8 are just wrong, and we can safely assume MAX_ARGS == 6 on linux. -- ldv
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