1) Add new rtld option to display error messages

[peterj]

Summary

The runtime linker internally saves details of errors it encounters but
these are are only exposed if dlerror(3) is called. Setting LD_PRINT_ERROR
to a non-empty string will automatically print all errors detected by the
runtime linker to stderr.

MFC after: 1 week

Test Plan

Compile the following code and execute with and without LD_PRINT_ERROR set
to a non-empty string. Note that the error is printed twice, apparently
because there's a second attempt to resolve the missing symbol during the
program cleanup.

---

#include <dlfcn.h>
#include <err.h>
#include <stdio.h>

int main(int argc, char **argv)
{

if (dlsym(NULL, "symbol_missing") != NULL)
    errx(1, "Found unexpected symbol");
return (0);

}

[kib]

I must note that for my whole-time usage of FreeBSD, I never needed such functionality. Rather, when I needed anything close to the proposed patch, I needed much more information, enabled by the LD_DEBUG knob. The only complication with LD_DEBUG is that we still do not compile rtld in this mode by default, but recompilation is trivial.

Also I am not convinced that adding a verbose features to the userspace runtime components is safe, the printing depends on too many assumptions about the program environment, like that the fd 2 is stderr, printing into it is safe etc.

Wouldn't utrace patch enough to diagnose ?

libexec/rtld-elf/rtld.c

457

Compare your usage of the LD prefix wrapping and the same usage one line above.

[wblock]

libexec/rtld-elf/rtld.1

205

Is this still valid if we make it more active?

to print error messages that are available to the application from

(Also avoiding "via", which only seems valid to me when given with a network or highway-type map.)

[peterj]

Based on kib's comments, I'll withdraw this revision. r312984 is similar functionality.

libexec/rtld-elf/rtld.c

457

That's what I get for forward-porting a patch and not adequately verifying changes.