Hi Rui,
On Sat, 14 Jan 2023, Rui Ueyama wrote:
On Sat, 7 Jan 2023, Rui Ueyama wrote:
It looks like compiler-generated code always uses `b`, `bl` or `blx`
instructions for function calls. These instructions have a 24-bit
immediate and therefore can jump anywhere between PC +- 16 MiB.
This hand-written assembly code instead uses `bge` and `beq` for
interprocedural jumps. Since these instructions have only a 19-bit
immediate (we have less bits for condition code), they can jump only
within PC +- 512 KiB. This sometimes causes a "relocation R_ARM_THM_JUMP19
out of range" error when linked with the mold linker. This error can
easily be avoided by using `b` instead of `bge` or `beq`.
Can you add a bit more explanation about what happens in mold in this case
and context about the setup - I don't quite understand how this can happen
(even if the code admittedly is a bit unusual)?
Since .L_swri_oldapi_conv_flt_to_s16_neon and
.L_swri_oldapi_conv_fltp_to_s16_2ch_neon are local symbols, they don't get
emitted by the assembler, and the branch instructions are encoded with
fixed offsets and no relocations. And even if there would be a relocation,
the destination is within the same text section chunk in the object file,
so it shouldn't be possible for it to be out of range.
The only possibility for this to be out of range, is if the destination is
treated as a global and routed via the PLC?
There was confusion on our side. ffmpeg used to contain two
audio_convert_neon.S as below
libswresample/arm/audio_convert_neon.S
libavresample/arm/audio_convert_neon.S
and the latter had a problem that I explained in the previous mail.
But that file has been removed, so there's no problem with the
existing code. I'll retract the patch I sent before. Sorry for the
confusion.
Ah, I see - that explains it!
Ok, good then, that there's no issue with that code pattern in assembly -
otherwise there could be a whole lot of issues to run into...
// Martin
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