Re: [FFmpeg-devel] [PATCH 6/7] avutil/riscv/asm: add generic push/pop helpers

[Niklas Haas <ffmpeg@haasn.xyz>]

On Tue, 13 Aug 2024 18:55:24 +0300 Rémi Denis-Courmont <remi@remlab.net> wrote:
> 
> 
> Le 13 août 2024 17:03:35 GMT+03:00, "J. Dekker" <jdek@itanimul.li> a écrit :
> >From: Niklas Haas <git@haasn.dev>
> >
> >Generic helper macros to push/pop multiple registers at once. Expands to
> >a single `addi` plus a sequence of XLEN-sized stores/loads.
> >---
> > libavutil/riscv/asm.S | 37 +++++++++++++++++++++++++++++++++++++
> > 1 file changed, 37 insertions(+)
> >
> >diff --git a/libavutil/riscv/asm.S b/libavutil/riscv/asm.S
> >index db190e99ca..3955530e4e 100644
> >--- a/libavutil/riscv/asm.S
> >+++ b/libavutil/riscv/asm.S
> >@@ -288,3 +288,40 @@
> >         .macro  count_args args:vararg
> >         count_args_inner 0, \args
> >         .endm
> >+
> >+        /**
> >+         * Helper macro to iterate over constant sized elements in memory
> >+         * @param op operation to perform on each element (sized load/store)
> >+         * @param size size in bytes per element
> >+         * @param offset starting offset of first element
> >+         * @param addr base address to load/store
> >+         * @param regs registers to iterate over
> >+         */
> >+        .macro  for_mem op, size, offset, addr, reg, regs:vararg
> >+        .ifnb \reg
> >+        \op     \reg, \offset(\addr)
> >+        for_mem \op, \size, \offset + \size, \addr, \regs
> >+        .endif
> >+        .endm
> >+
> >+        /**
> >+         * Push a variable number of registers to the stack.
> >+         * @param n number of registers to push
> >+         * @param regs registers to push
> >+         */
> >+        .macro  push regs:vararg
> >+        count_args \regs
> >+        addi    sp, sp, -(num_args * (__riscv_xlen >> 3))
> >+        for_mem sx, __riscv_xlen >> 3, 0, sp, \regs
> >+        .endm
> 
> This is not in line with the psABI specification for RV32 and RV64. Ditto below.

Missing alignment to multiples of 16 bytes, what else?

> 
> It's also not in line with the RV128 ABI since that doesn't even exist yet.
> 
> >+
> >+        /**
> >+         * Pop a variable number of registers from the stack.
> >+         * @param n number of registers to pop
> >+         * @param[out] regs registers to pop
> >+         */
> >+        .macro  pop regs:vararg
> >+        count_args \regs
> >+        for_mem lx, __riscv_xlen >> 3, 0, sp, \regs
> >+        addi    sp, sp, num_args * (__riscv_xlen >> 3)
> >+        .endm
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