On 9/23/20 7:38 AM, Florian Weimer via Libc-alpha wrote: > Returning its argument without further checks is almost always > wrong for la_version. What you write here is the way I understand the interface to work. As Andreas noted there is one typo. I suggest changing the example to match, otherwise people might keep cribbing that code ;-) > Signed-off-by: Florian Weimer <fweimer@xxxxxxxxxx> > I agree that la_version should return LAV_CURRENT, that is the expected way to implement the function, and returning less than LAV_CURRENT is required to implement older interfaces and be more compatible with older releases. As an example I encouraged Ludovic to solve a Guix path problem with LD_AUDIT and you can see it here: https://issues.guix.gnu.org/41189 +unsigned int +la_version (unsigned int v) +{ + if (v != LAV_CURRENT) + error (1, 0, "cannot handle interface version %u", v); + ... + return v; +} While this is OK, in that if it's not an exact match the audit module errors out, or if it is a match returns v which is LAV_CURRENT. It could have been more relaxed: if (v < LAV_CURRENT) error (...) ... return LAV_CURRENT; Your changes here int he man page would have clarified that to some extent. > --- > man7/rtld-audit.7 | 31 ++++++++++++++++++++++--------- > 1 file changed, 22 insertions(+), 9 deletions(-) > > diff --git a/man7/rtld-audit.7 b/man7/rtld-audit.7 > index b1b7dfebc..ca8afa752 100644 > --- a/man7/rtld-audit.7 > +++ b/man7/rtld-audit.7 > @@ -70,17 +70,30 @@ the auditing library. > When invoking this function, the dynamic linker passes, in > .IR version , > the highest version of the auditing interface that the linker supports. > -If necessary, the auditing library can check that this version > -is sufficient for its requirements. > .PP > -As its function result, > -this function should return the version of the auditing interface > -that this auditing library expects to use (returning > +A typical implementation of this function simply returns the constant > +.BR LAV_CURRENT , > +which indicates the version of > +.I <link.h> > +that was used to build the audit module. If the dynamic linker does > +not support this version of the audit interface, it will refuse to > +activate this audit module. If the function returns zero, the dynamic > +linker also does not activate this audit module. > +.PP > +In order to enable backwards compatibility with older dynamic linkers, > +an audit module can examine the > +.I version > +argument and return an earlier version than > +.BR LAV_CURRENT , > +assuming the module can adjust its implement to match the requirements s/implement/implementation/g (Andreas caught this in his review) > +of the previous version of the audit interface. The > +.B la_version > +function should not return the value of > .I version > -is acceptable). > -If the returned value is 0, > -or a version that is greater than that supported by the dynamic linker, > -then the audit library is ignored. > +without further checks because it could correspond to an interface > +that does not match the > +.I <link.h> > +definitions used to build the audit module. > .SS la_objsearch() > \& > .nf > May I additionally suggest something like this to the example? diff --git a/man7/rtld-audit.7 b/man7/rtld-audit.7 index b1b7dfebc..8a4008b2a 100644 --- a/man7/rtld-audit.7 +++ b/man7/rtld-audit.7 @@ -510,7 +510,11 @@ la_version(unsigned int version) { printf("la_version(): %u\en", version); - return version; + if (version > LAV_CURRENT) + printf ("la_version(): rtld supports newer interfaces.\n"); + + /* Request the version we knew about at compile time. */ + return LAV_CURRENT; } char * --- Post a v2? -- Cheers, Carlos.
