When I run the editor with

valgrind --keep-debuginfo=yes --trace-children=yes ./local/godot/bin/godot.linuxbsd.editor.dev.x86_64

I see a number of Invalid read of size 8 reports, they are all inside a call to dl_open, e.g.

Invalid read of size 8
at 0xBDA8708: strncmp (strcmp.S:172)
by 0xBD8668D: is_dst (dl-load.c:216)
by 0xBD8810E: _dl_dst_count (dl-load.c:253)
by 0xBD8810E: expand_dynamic_string_token (dl-load.c:395)
by 0xBD882B7: fillin_rpath.isra.0 (dl-load.c:483)
by 0xBD88602: decompose_rpath (dl-load.c:654)
by 0xBD8ABF5: cache_rpath (dl-load.c:696)
by 0xBD8ABF5: cache_rpath (dl-load.c:677)
by 0xBD8ABF5: _dl_map_object (dl-load.c:2165)
by 0xBD83494: openaux (dl-deps.c:64)
by 0xC849C47: _dl_catch_exception (dl-error-skeleton.c:208)
by 0xBD83C7B: _dl_map_object_deps (dl-deps.c:248)
by 0xBD8EA0E: dl_open_worker_begin (dl-open.c:592)
by 0xC849C47: _dl_catch_exception (dl-error-skeleton.c:208)
by 0xBD8DF99: dl_open_worker (dl-open.c:782)
Address 0x13c628a9 is 9 bytes inside a block of size 15 alloc'd
at 0xC5C8899: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
by 0xBDA723F: malloc (rtld-malloc.h:56)
by 0xBDA723F: strdup (strdup.c:42)
by 0xBD88594: decompose_rpath (dl-load.c:629)
by 0xBD8ABF5: cache_rpath (dl-load.c:696)
by 0xBD8ABF5: cache_rpath (dl-load.c:677)
by 0xBD8ABF5: _dl_map_object (dl-load.c:2165)
by 0xBD83494: openaux (dl-deps.c:64)
by 0xC849C47: _dl_catch_exception (dl-error-skeleton.c:208)
by 0xBD83C7B: _dl_map_object_deps (dl-deps.c:248)
by 0xBD8EA0E: dl_open_worker_begin (dl-open.c:592)
by 0xC849C47: _dl_catch_exception (dl-error-skeleton.c:208)
by 0xBD8DF99: dl_open_worker (dl-open.c:782)
by 0xC849C47: _dl_catch_exception (dl-error-skeleton.c:208)
by 0xBD8E34D: _dl_open (dl-open.c:883)

It happens when starting the editor, before loading a project. Is this concerning? I'm having malloc issues with one of my own shared libraries, that is why I ask.

Later I also see Conditional jump or move depends on uninitialised value(s) and Syscall param writev(vector[...]) points to uninitialised byte(s) reports.

Thanks a lot!

Considering these seem to happen deep inside the code for dl_open() I wouldn't worry too much about them.
In fact, looking a bit around I found a SO thread with the very same stacktrace running SDL. Check the accepted answer there, which I'll just quote here:

Considering the source file and function names in the associated stack traces, the "invalid read" errors appear to be occurring inside the dynamic loader. Not only is that not the fault of your code, it probably isn't [SDL's] Godot's fault, either.