Can't we just add libsys.so to the /usr/lib/libc.so linker script? That would 
work for everything except static linking?

-Dimitry

> On 21 Feb 2024, at 21:00, Brooks Davis <bro...@freebsd.org> wrote:
> 
> TL;DR: you can work around this by adding -lsys to the link line and I
> aim to improve the situation soon.
> 
> The sanitizers reach somewhat questionably into libc internals that are
> exported to allow rtld to update them.  I was unable to find an solution
> that didn't break this and I felt that fixing things like closefrom()
> using non-deprecated syscalls was more important than avoiding changes
> to the sanitizer interface.
> 
> I'm trying to find a way to better solution to the sanitizer.  A few
> ideas I'm considering:
> - Teach clang to add -lsys when linking with sanitizers on sufficently
>   new systems (con: doesn't fix gcc).
> - Make the symbol weak in the sanitizer and complain when it's not
>   found or call back to using environ.  The latter migth have
>   limitations around direct exec with rtld.
> - Relocate __elf_aux_vector to csu so the symbol is always available.
> - Adding a new interface to access __elf_aux_vector directly.
> 
> I'll continue to work on this.
> 
> -- Brooks
> 
> On Wed, Feb 21, 2024 at 09:52:23AM +0000, hartmut.bra...@dlr.de wrote:
>> Hi,
>> 
>> I updated yesterday and now event a minimal program with
>> 
>> cc -fsanitize=address
>> 
>> produces
>> 
>> ld: error: undefined symbol: __elf_aux_vector
>>>>> referenced by sanitizer_linux_libcdep.cpp:950 
>>>>> (/usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:950)
>>>>>              sanitizer_linux_libcdep.o:(__sanitizer::ReExec()) in archive 
>>>>> /usr/lib/clang/17/lib/freebsd/libclang_rt.asan-x86_64.a
>> cc: error: linker command failed with exit code 1 (use -v to see invocation)
>> 
>> I think this is caused by the libsys split.
>> 
>> Cheers,
>> Harti
>> 
>> -----Original Message-----
>> From: owner-freebsd-curr...@freebsd.org <owner-freebsd-curr...@freebsd.org> 
>> On Behalf Of Brooks Davis
>> Sent: Friday, February 2, 2024 11:32 PM
>> To: curr...@freebsd.org
>> Subject: libc/libsys split coming soon
>> 
>> TL;DR: The implementation of system calls is moving to a seperate library 
>> (libsys).  No changes are required to existing software (except to ensure 
>> that libsys is present when building custom disk images).
>> 
>> Code: https://github.com/freebsd/freebsd-src/pull/908
>> 
>> After nearly a decade of intermittent work, I'm about to land a series of 
>> patches which moves system calls, vdso support, and libc's parsing of the 
>> ELF auxiliary argument vector into a separate library (libsys).  I plan to 
>> do this early next week (February 5th).
>> 
>> This change serves three primary purposes:
>>  1. It's easier to completely replace system call implementations for
>>     tracing or compartmentalization purposes.
>>  2. It simplifies the implementation of restrictions on system calls such
>>     as those implemented by OpenBSD's msyscall(2)
>>     (https://man.openbsd.org/msyscall.2).
>>  3. It allows language runtimes to link with libsys for system call
>>     implementations without requiring libc.
>> 
>> libsys is an auxiliary filter for libc.  This means that for any symbol 
>> defined by both, the libsys version takes precedence at runtime.  For system 
>> call implementations, libc contains empty stubs.  For others it contains 
>> copies of the functions (this could be further refined at a later date).  
>> The statically linked libc contains the full implementations so linking 
>> libsys is not required.
>> 
>> Additionally, libthr is now linked with libsys to provide _umtx_op_err().
>> 
>> The overall implementation follows https://reviews.freebsd.org/D14609,
>> but is redone from scratch as multiple commits to facilitate review and 
>> assist git's rename detection.
>> 
>> Testing:
>>  - Boot testing on amd64, aarch64, and riscv
>>  - make tinderbox (prior version, final run in progress)
>>  - exp-run: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=276391
>>  - Kyua tests in poudriere amd64 jails: same 359 failures as with the
>>    latest freebsdci build
>> 
>> Thanks to Ali Mashtizadeh and Tal Garfinkel for D14609 and many apologies 
>> for not landing this in a timely manner.  Additional thanks to kib@ for many 
>> rounds of review, markj@ and kib@ for debugging rtld issues exposed by this 
>> patch, and antoine@ for exp-runs.
>> 
>> Future work:
>>  - Purely functional interfaces to system calls (no errorno).
>>    Unfortunately there isn't an obvious way to do this without
>>    significant (possibly generated) assembly code.
>>  - Investigate msyscall(2) and pinsyscalls(2).
>>  - Reduce the size of stubs in libc.  I????????ve errored on the
>>    side of not touching the copies that end up in libc to keep diff
>>    size down.  We might want to generate empty stubs instead.
>> 
>> See also:
>>  - Solaris Linker and Libraries Guide:
>>    https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter4-4.html
>> 
>> -- Brooks



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