[DTrace-devel] [PATCH] Provide the maximum string length as BPF symbol STRSZ

[Kris Van Hees]

On Fri, Aug 20, 2021 at 12:16:05PM -0400, Eugene Loh wrote:
> Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
> though the value isn't so much provided by STRSZ as by &STRSZ.  So, the 
> subject line could perhaps be a little more precise, though I suppose it 
> doesn't matter.  Good enough as is.

It is provided by the STRSZ symbol, but the way we need to access use it is
as &STRSZ because of the way we use relocations for this.  So yes, it does not
matter.  I am documenting it from the implementtion side where the symbol that
gets added to the list of symbols and to the reloc resolver is named STRSZ.

> On 8/20/21 2:46 AM, Kris Van Hees wrote:
> > Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> > ---
> >   libdtrace/dt_bpf.h   | 7 ++++---
> >   libdtrace/dt_cc.c    | 4 ++++
> >   libdtrace/dt_dlibs.c | 1 +
> >   3 files changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/libdtrace/dt_bpf.h b/libdtrace/dt_bpf.h
> > index dcc82b80..68e4aa07 100644
> > --- a/libdtrace/dt_bpf.h
> > +++ b/libdtrace/dt_bpf.h
> > @@ -23,9 +23,10 @@ extern "C" {
> >   #define DT_CONST_CLID	3
> >   #define DT_CONST_ARGC	4
> >   #define DT_CONST_STBSZ	5
> > -#define DT_CONST_STKOFF	6
> > -#define DT_CONST_STKSIZ	7
> > -#define DT_CONST_BOOTTM	8
> > +#define DT_CONST_STRSZ	6
> > +#define DT_CONST_STKOFF	7
> > +#define DT_CONST_STKSIZ	8
> > +#define DT_CONST_BOOTTM	9
> >   
> >   extern int perf_event_open(struct perf_event_attr *attr, pid_t pid, int cpu,
> >   			   int group_fd, unsigned long flags);
> > diff --git a/libdtrace/dt_cc.c b/libdtrace/dt_cc.c
> > index 2a6904a0..f69c750d 100644
> > --- a/libdtrace/dt_cc.c
> > +++ b/libdtrace/dt_cc.c
> > @@ -2348,6 +2348,10 @@ dt_link_construct(dtrace_hdl_t *dtp, const dt_probe_t *prp, dtrace_difo_t *dp,
> >   			case DT_CONST_STBSZ:
> >   				nrp->dofr_data = dtp->dt_strlen;
> >   				continue;
> > +			case DT_CONST_STRSZ:
> > +				nrp->dofr_data =
> > +					dtp->dt_options[DTRACEOPT_STRSIZE];
> > +				continue;
> >   			case DT_CONST_STKOFF:
> >   				nrp->dofr_data = roundup(dtp->dt_maxreclen, 8);
> >   				continue;
> > diff --git a/libdtrace/dt_dlibs.c b/libdtrace/dt_dlibs.c
> > index 35a18596..53abe2f7 100644
> > --- a/libdtrace/dt_dlibs.c
> > +++ b/libdtrace/dt_dlibs.c
> > @@ -78,6 +78,7 @@ static const dt_ident_t		dt_bpf_symbols[] = {
> >   	DT_BPF_SYMBOL_ID(CLID, DT_IDENT_SCALAR, DT_CONST_CLID),
> >   	DT_BPF_SYMBOL_ID(ARGC, DT_IDENT_SCALAR, DT_CONST_ARGC),
> >   	DT_BPF_SYMBOL_ID(STBSZ, DT_IDENT_SCALAR, DT_CONST_STBSZ),
> > +	DT_BPF_SYMBOL_ID(STRSZ, DT_IDENT_SCALAR, DT_CONST_STRSZ),
> >   	DT_BPF_SYMBOL_ID(STKOFF, DT_IDENT_SCALAR, DT_CONST_STKOFF),
> >   	DT_BPF_SYMBOL_ID(STKSIZ, DT_IDENT_SCALAR, DT_CONST_STKSIZ),
> >   	DT_BPF_SYMBOL_ID(BOOTTM, DT_IDENT_SCALAR, DT_CONST_BOOTTM),
> 
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