"H.J. Lu" <hjl.to...@gmail.com> wrote: >On Mon, Mar 18, 2013 at 10:02 AM, Paul Pluzhnikov ><ppluzhni...@google.com> wrote: >> +cc libc-alpha >> >> On Mon, Mar 18, 2013 at 9:05 AM, Xinliang David Li ><davi...@google.com> wrote: >>> Interesting idea about lazy IFUNC relocation. >> >>> On Mon, Mar 18, 2013 at 2:02 AM, Richard Biener >>> <richard.guent...@gmail.com> wrote: >> >>>> On Fri, Mar 15, 2013 at 10:55 PM, Sriraman Tallam ><tmsri...@google.com> wrote: >> >>>>> This patch is meant for google/gcc-4_7 but I want this to be >>>>> considered for trunk when it opens again. This patch makes it easy >to >>>>> test for code coverage of multiversioned functions. Here is a >>>>> motivating example: >> >>>> Err. As we are using IFUNCs isn't it simply possible to do this in >>>> the dynamic loader - for example by simlply pre-loading a library >>>> with the IFUNC relocators implemented differently? Thus, shouldn't >>>> we simply provide such library as a convenience? >> >> A similar need exists in glibc itself: it too has multiversioned >functions, >> and lack of testing has led to recent bugs in some of them. >> >> HJ has added a framework to test IFUNCs to glibc late last year, but >it >> would be nice to have a more general IFUNC control, so I could e.g. >run >> a binary on SSE4-capable machine A as that binary would run on >SSE2-only >> capable machine B. >> >> (We've had a few bugs recently, were the crash would only show on >machine >> B and not A. These are a pain to debug, as I may not have access to >B.) >> >> If such a controller is implemented, I'd think it would have to be >part >> of GLIBC (or part of the ld-linux itself), and not of libgcc. >> >> LD_CPU_FEATURES=sse,sse2 ./a.out # run as if only sse and sse2 are >available >> > >We can pass environment variables to IFUNC selector. Maybe we can >enable it for debug build.
I was asking for the ifunc selector to be Overridable by ld_preload or a similar mechanism at dynamic load time. Richard.
