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Linker magic for aliases an external symbol... how to?


I'm packaging a daemon (a Tacacs+ proxy for SSSD authentication, if anyone is interested) and using the libtac library.

I'm using an external packaging of libtac (as a .so) which was compiled with -DTACDEBUG_AT_RUNTIME=1 which had the net effect of causing the tracing macro TACDEBUG() to expand to:

#define TACDEBUG(level, format, ...) \
do { if (tac_debug_enable) logmsg(level, format, ## __VA_ARGS__); } while (0)

problem is, the daemon doesn't provide the logmsg() function... but it does link to libc and hence provides syslog()... And yes, "level" corresponds to LOG_xxxx in <syslog.h> in the sources of the library. And no, I can't recompile or otherwise modify I need to use it as is.

I've tried several different ways to specify at either compile time or link time that I want logmsg to be an alias to syslog().

I've tried in main.c:

void logmsg(int, const char *, ...)    asm("syslog");


void logmsg(int, const char *, ...) __attribute__ ((weak, alias ("syslog")));

as well as various link-time options like:


as well as:


where contains:

  .text :
      logmsg = syslog;


I looked around on google, codebase, stackoverflow, etc. and couldn't find a solution to this problem (external library [libtac] referencing external symbol (logmsg) that I want to alias to an entry point (syslog) in another library, in this case libc).

With all of the options that gcc and ld provide, I was sure I'd be able to do this but now it's looking like I'll have to use objcopy to do some --redefine-sym magic... but I'm not even sure I can do that since libtac is a shared-object library and I don't want to rewrite that...

Seems there's no good solution that I can find. Can someone please tell me the correct way to resolve (no pun intended) this dilemma?



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