gcc - Using LD_PRELOAD to overload call to a C function of a shared library -

-

i'm following this answer override call c function of c library.

i think did correctly, doesn't work:

i want override "dibopen"-function. code of library pass ld_preload environment-variable when running application:

dibstatus dibopen(void **ctx, enum board b) {     printf("look @ me, wrapped\n");      static dibstatus (*func)(void **, enum board) = null;     if(!func)         func = dlsym(rtld_next, "dibopen");     printf("overridden!\n");     return func(pcontextaddr, boardtype, boardhdl); }

the output of nm lib.so | grep dibopen shows

000000000001d711 t dibopen

when run program this

ld_preload=libpreload.so ./program

i link program -ldl ldd program not show link libdl.so

it stops with

 symbol lookup error: libpreload.so: undefined symbol: dlsym

. can debug further? mistake?

when create shared library (whether or not used in ld_preload), need name of libraries it needs resolve dependencies. (under circumstances, dlopened shared object can rely on executable provide symbols it, best practice not rely on this.) in case, need link libpreload.so against libdl. in makefile-ese:

libpreload.so: x.o y.o z.o         $(cc) -shared -wl,-z,defs -wl,--as-needed -o $@ $^ -ldl

the option -wl,-z,defs tells linker should issue error if shared library has unresolved undefined symbols, future problems of type caught earlier. option -wl,--as-needed tells linker not record dependency on libraries don't satisfy undefined symbols. both of these should on default, historical reasons, aren't.


Popular posts from this blog

How to calculate SNR of signals in MATLAB? -

-
i've encountered simple, yet fundamental problem on calculating snr: there several signals : s1 = original , pure clean signal without noise. n1 = white gaussian noise going added s1. s2 = s1 + n1 (the noisy signal before performing noise-reduction algorithm) s3 = noise-reduced signal (after performing noise reduction algorithm) n2 = s3 - s1 (the amount of noise after performing noise-reduction algorithm) now want compare snr before , after performing noise-reduction algorithm. which signals should consider snr_before!? s1/n1 or s2/n1 ? which signals should consider snr_after!? s3/n1 or s3/n2 ? which commands or functions should use in matlab in order compute snr_before , snr_after? thanks billion putting time on helping me. what know calculating snr before : snrbeforenoise = mean( signal .^ 2 ) / mean( noise .^ 2 ); and snr after : residual_noise = signal - noise_reduced_signal; snr_after = mean( signal .^ 2 ) / mean( residual_noise .^ 2
Read more

c# - Attempting to upload to FTP: System.Net.WebException: System error -

-
i have api takes in xml , uploads files based on information in xml. uploads on schedule (also xml), , have tested surrounding , know works. i getting error 40% of time on first file attempt upload in each time cycle (time cycle = 45 minutes files, 30 minutes others). here code upload: try { loggerftp.log("uploading file: " + filename, false); // create request. ftpwebrequest request = (ftpwebrequest)webrequest.create(appsettingsftp.ftpurl + @"/" + filename); request.method = webrequestmethods.ftp.uploadfile; request.timeout = 6000000; //set 100 minutes //request.timeout = -1; //set infinite // add login credentials. request.credentials = new networkcredential(appsettingsftp.ftplogin, appsettingsftp.ftppassword); // grab file contents. streamreader sourcestream = new streamreader(appsettingsftp.uploadfiledirectory + filename); byte[] filecontents = encoding.utf8.getbytes(sourcestream.readtoend()); sourcest
Read more

ios - UISlider customization: how to properly add shadow to custom knob image -

-
Image
i need place custom knob image shadow uislider. far have image of 38x38, of there region defines shadow of knob. now while using image, when slide knob extreme ends actual knob not able cover end points, hence end points visible under transparent region of knob image this code using customize uislider uiimage *slidebtimg = [uiimage imagenamed:sliderknobimg]; [self.ratingslider setthumbimage:slidebtimg forstate:uicontrolstatenormal]; [self.ratingslider setthumbimage:slidebtimg forstate:uicontrolstatehighlighted]; how can implement custom knob shadow beneath it, covering end points?? look inside uislider.h , there methods let customize slider knob , track needed. (ios 2.0 , above) // lets subclass lay out track , thumb needed - (cgrect)minimumvalueimagerectforbounds:(cgrect)bounds; - (cgrect)maximumvalueimagerectforbounds:(cgrect)bounds; - (cgrect)trackrectforbounds:(cgrect)bounds; - (cgrect)thumbrectforbounds:(cgrect)bounds trackrect:(cgrect)rect value:
Read more