Extended Description

$ cat f.c
void f() {}

$ clang -c f.c
$ ld.lld -shared --defsym=g=f f.o
$ objdump -T a.out
DYNAMIC SYMBOL TABLE:
00000000000012a0 g DF .text 0000000000000006 f
00000000000012a0 g D .text 0000000000000000 g

f is marked STT_FUNC, but g is not. It might be hard to do in the general case (where e.g. you can have arithmetic in the defsym expression), but in this case, it seems desirable for the alias to get the same symbol type as the original.

From Peter Smith:

There can be a problem on Arm as no interworking will be performed for symbols that are not STT_FUNC.

$ cat h.c
extern void f();
extern void g();
void h() { f(); g(); }

$ clang --target=armv7a-none-eabi -c f.c
$ clang --target=armv7a-none-eabi -c h.c -mthumb
$ ld.lld f.o h.o --defsym g=f # No --shared to prevent a PLT entry.
$ objdump -d a.out
000200e8 :
200e8: b580 push {r7, lr}
200ea: 466f mov r7, sp
200ec: f7ff effa blx 200e4
200f0: f7ff fff8 bl 200e4
200f4: bd80 pop {r7, pc}

The blx to f() is correct as a state change is required. The bl to f() will likely crash the program.

ld.bfd correctly marks g as STT_FUNC so it gets the state change correct for both calls.
00008004 :
8004: b580 push {r7, lr}
8006: 466f mov r7, sp
8008: f7ff effa blx 8000
800c: f7ff eff8 blx 8000
8010: bd80 pop {r7, pc}