Configure misidentifies clock_gettime and getentropy on macOS Sierra/XCode8 when compiling for iOS 8

libSystem.dylib provides clock_gettime and getentropy from iOS 10 onward but not below but the configure script does not detect that. Even with the -Wl,-no_weak_imports

linker flag. The only way I managed to compile for iOS8 and iOS9 on macOS Sierra with XCode8 was to patch out detection of clock_gettime and getentropy from the configure script. This is less-than-ideal but the only fix I know. I attached the patch that I used on configure.

Trac:
Username: rainwolf

changed milestone to %Tor: 0.2.9.x-final

added 028-backport 8 Sierra XCode clock_gettime component::core tor/tor getentropy libSystem.dylib milestone::Tor: 0.2.9.x-final osx priority::medium reporter::rainwolf resolution::fixed severity::normal status::closed type::defect version::tor 0.2.8.8 labels

Trac:
Username: rainwolf

tor-configure.diff

configure patch

Trac:
Username: rainwolf

(#20241 (moved) is related to this, but not the same.)

Does Apple provide a general way to target a specific version of their APIs, other than downgrading your developer tools?

Trac:
Milestone: N/A to Tor: 0.2.9.x-final
Keywords: libSystem.dylib deleted, libSystem.dylib 028-backport added

Trac:
Component: Core Tor to Core Tor/Tor
Keywords: libSystem.dylib 028-backport deleted, libSystem.dylib 028-backport osx added

Replying to nickm:

They mention here that the new linker flag -Wl,-no_weak_imports should fail to link if the link would be a leak link. (This happens when you use the Apple-supplied headers and they indicate the symbol was added after your current deployment target.)

This should cause the tests for clock_gettime and getentropy to fail correctly if you were to target an OS version that doesn't supply them.

(#20241 (moved) is related to this, but not the same.)

Does Apple provide a general way to target a specific version of their APIs, other than downgrading your developer tools?

Trac:
Username: rainwolf

Oh! Hm.

I tried making an example program as small as possible to still use getentropy():

#include <sys/types.h>
#include <sys/random.h>
#include <stdio.h>

int main(int argc, char **argv)
{
  unsigned x;
  if (getentropy(&x, sizeof(x)) < 0)
    perror("getentropy");
  else
    printf("%u\n", x);
  return 0;
}

I tried compiling it in lots of different ways, but I couldn't find a way to tell gcc to ignore the presence of getentropy()....

% gcc -Wall -Wl,-no_weak_imports getentropy_test.c -o get
% gcc -Wall -mmacosx-version-min=10.10 -Wl,-no_weak_imports getentropy_test.c -o get
% ( export MACOSX_DEPLOYMENT_TARGET=10.10 ; gcc -Wall -mmacosx-version-min=10.10 -Wl,-no_weak_imports getentropy_test.c -o get )

I wonder if Apple messed up somehow and forgot to tag these APIs as 10.12 only? Or maybe I'm doing something wrong with the above.

This is broken on Tor 0.2.8.9 too, right? So it's not a regression?

It seems smart to get Tor building on this new esoteric platform with its new bugs, so we will have a Tor stable that builds on it. But also it seems smart to not let this ticket hold up the 0.2.9 stable if it's the only ticket remaining and we haven't solved it by then.

Replying to nickm:

Oh! Hm.

I tried making an example program as small as possible to still use getentropy(): {{{ #include <sys/types.h> #include <sys/random.h> #include <stdio.h>

int main(int argc, char **argv) { unsigned x; if (getentropy(&x, sizeof(x)) < 0) perror("getentropy"); else printf("%u\n", x); return 0; } }}}

I tried compiling it in lots of different ways, but I couldn't find a way to tell gcc to ignore the presence of getentropy().... {{{ % gcc -Wall -Wl,-no_weak_imports getentropy_test.c -o get % gcc -Wall -mmacosx-version-min=10.10 -Wl,-no_weak_imports getentropy_test.c -o get % ( export MACOSX_DEPLOYMENT_TARGET=10.10 ; gcc -Wall -mmacosx-version-min=10.10 -Wl,-no_weak_imports getentropy_test.c -o get ) }}}

I wonder if Apple messed up somehow and forgot to tag these APIs as 10.12 only? Or maybe I'm doing something wrong with the above.

Yes, Apple messed up and forgot to tag the APIs. So any tor built on Sierra won't run on older OS X.

So it's a platform bug, not a tor version bug. Let's fix it if we can, probably by testing MACOSX_DEPLOYMENT_TARGET ourselves (ugh).

Possible fix in branch sierra_fix_028 in my public repository. I haven't tested it on OSX yet though.

Trac:
Status: new to needs_review

For the record, my github branch weak_link_getentropy is an alternative solution.

But I think it's much more complex in the clock_gettime case, and in general, it has more failure modes, so I would prefer nickm's solution.

I have reviewed nickm's branch and it looks good, but I have no OS X 10.11 or earlier to test it on.

(To test, we need to compile on macOS 10.12 with export MACOSX_DEPLOYMENT_TARGET=10.11, then try to run the binary on an earlier OS X version.)

Merged to maint-0.2.8 and forward.

Trac:
Status: needs_review to closed
Resolution: N/A to fixed

closed

mentioned in issue #20241 (moved)

mentioned in issue #26251 (moved)

mentioned in issue #26876 (moved)

moved to tpo/core/tor#20235 (closed)