There are a few assembler files in the hotspot tree:
$ find src/hotspot/ -name \*.S -o -name \*.s
src/hotspot/os_cpu/linux_x86/linux_x86_64.s
src/hotspot/os_cpu/linux_x86/linux_x86_32.s
src/hotspot/os_cpu/linux_sparc/linux_sparc.s
src/hotspot/os_cpu/bsd_x86/bsd_x86_32.s
src/hotspot/os_cpu/bsd_x86/bsd_x86_64.s
src/hotspot/os_cpu/linux_arm/linux_arm_32.s
src/hotspot/os_cpu/linux_arm/linux_arm_64.s
src/hotspot/os_cpu/solaris_sparc/solaris_sparc.s
src/hotspot/os_cpu/solaris_x86/solaris_x86_64.s
src/hotspot/os_cpu/linux_aarch64/threadLS_linux_aarch64.s
src/hotspot/os_cpu/linux_aarch64/copy_linux_aarch64.s
src/hotspot/os_cpu/linux_aarch64/linux_aarch64.S
src/hotspot/cpu/aarch64/aarch64_linkage.S

However, when assembling them and configuring with:
--with-native-debug-symbols=internal
no debug info gets generated. Other files contain debug info as expected.

Example for SpinPause which is in linux_x86_64.s:

$ gdb -ex 'set confirm off' -ex 'handle SIGSEGV pass nostop noprint' -ex 'set breakpoint pending on' -ex 'break SpinPause' -ex 'run' -ex 'bt' -ex 'quit' --args ./build/linux-x86_64-normal-server-release/images/jdk/bin/java -version
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Reading symbols from ./build/linux-x86_64-normal-server-release/images/jdk/bin/java...done.
Signal Stop Print Pass to program Description
SIGSEGV No No Yes Segmentation fault
Function "SpinPause" not defined.
Breakpoint 1 (SpinPause) pending.
Starting program: /disk/openjdk/upstream-sources/openjdk-head/build/linux-x86_64-normal-server-release/images/jdk/bin/java -version
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x7ffff7fc8700 (LWP 129968)]
[New Thread 0x7fffd85c7700 (LWP 129969)]
[New Thread 0x7fffc1657700 (LWP 129970)]
[New Thread 0x7fffc1555700 (LWP 129971)]
[New Thread 0x7fffc0c4b700 (LWP 129972)]
[New Thread 0x7fffc0b49700 (LWP 129973)]
[New Thread 0x7fffc0247700 (LWP 129974)]
[Switching to Thread 0x7fffc0c4b700 (LWP 129972)]

Thread 6 "G1 Refine#0" hit Breakpoint 1, 0x00007ffff689ccc0 in SpinPause () from /disk/openjdk/upstream-sources/openjdk-head/build/linux-x86_64-normal-server-release/images/jdk/lib/server/libjvm.so
#0 0x00007ffff689ccc0 in SpinPause () at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/runtime/mutex.cpp:1200
#1 0x00007ffff69d144d in Monitor::TrySpin (this=this@entry=0x7ffff000c780, Self=Self@entry=0x7ffff01e0800) at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/runtime/mutex.cpp:361
#2 0x00007ffff69d17a3 in Monitor::TrySpin (Self=0x7ffff01e0800, this=0x7ffff000c780) at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/runtime/os.hpp:229
#3 Monitor::ILock (this=0x7ffff000c780, Self=0x7ffff01e0800) at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/runtime/mutex.cpp:450
#4 0x00007ffff69d1c6f in Monitor::IWait (this=this@entry=0x7ffff000c780, Self=Self@entry=0x7ffff01e0800, timo=timo@entry=1)
    at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/runtime/mutex.cpp:818
#5 0x00007ffff69d2bd9 in Monitor::wait (this=0x7ffff000c780, no_safepoint_check=no_safepoint_check@entry=true, timeout=timeout@entry=1, as_suspend_equivalent=as_suspend_equivalent@entry=false)
    at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/runtime/mutex.cpp:1097
#6 0x00007ffff64c33a8 in ConcurrentGCThread::wait_for_universe_init (this=0x7ffff01e0800) at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/gc/shared/concurrentGCThread.cpp:62
#7 ConcurrentGCThread::run (this=0x7ffff01e0800) at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/share/gc/shared/concurrentGCThread.cpp:79
#8 0x00007ffff6a189f0 in thread_native_entry (thread=0x7ffff01e0800) at /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/os/linux/os_linux.cpp:698
#9 0x00007ffff79a7594 in start_thread () from /lib64/libpthread.so.0
#10 0x00007ffff72c702f in clone () from /lib64/libc.so.6

Note this:

SpinPause () from /disk/openjdk/upstream-sources/openjdk-head/build/linux-x86_64-normal-server-release/images/jdk/lib/server/libjvm.so

Should be something like this:

SpinPause () from /disk/openjdk/upstream-sources/openjdk-head/src/hotspot/os_cpu/linux_x86/linux_x86_64.s:45