Re: [PATCH 02/10] gdbstub: introduce target independent gdb register helper

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2025/03/20 3:22, Alex Bennée wrote:
> The current helper.h functions rely on hard coded assumptions about
> target endianess to use the tswap macros. We also end up double
> swapping a bunch of values if the target can run in multiple endianess
> modes. Avoid this by getting the target to pass the endianess and size
> via a MemOp and fixing up appropriately.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

The overall idea looks good to me. I have a few nitpicks:

> ---
>   include/gdbstub/registers.h | 30 ++++++++++++++++++++++++++++++
>   gdbstub/gdbstub.c           | 22 ++++++++++++++++++++++
>   2 files changed, 52 insertions(+)
>   create mode 100644 include/gdbstub/registers.h
> 
> diff --git a/include/gdbstub/registers.h b/include/gdbstub/registers.h
> new file mode 100644
> index 0000000000..4abc7a6ae7
> --- /dev/null
> +++ b/include/gdbstub/registers.h
> @@ -0,0 +1,30 @@
> +/*
> + * GDB Common Register Helpers
> + *
> + * Copyright (c) 2025 Linaro Ltd
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#ifndef GDB_REGISTERS_H
> +#define GDB_REGISTERS_H
> +
> +#include "exec/memop.h"
> +
> +/**
> + * gdb_get_register_value() - get register value for gdb
> + * mo: size and endian MemOp
> + * buf: GByteArray to store in target order
> + * val: pointer to value in host order
> + *
> + * This replaces the previous legacy read functions with a single
> + * function to handle all sizes. Passing @mo allows the target mode to
> + * be taken into account and avoids using hard coded tswap() macros.
> + *
> + * Returns the number of bytes written to the array.
> + */
> +int gdb_get_register_value(MemOp op, GByteArray *buf, uint8_t *val);
> +
> +#endif /* GDB_REGISTERS_H */
> +
> +
> diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
> index 282e13e163..3d7b1028e4 100644
> --- a/gdbstub/gdbstub.c
> +++ b/gdbstub/gdbstub.c
> @@ -32,6 +32,7 @@
>   #include "exec/gdbstub.h"
>   #include "gdbstub/commands.h"
>   #include "gdbstub/syscalls.h"
> +#include "gdbstub/registers.h"
>   #ifdef CONFIG_USER_ONLY
>   #include "accel/tcg/vcpu-state.h"
>   #include "gdbstub/user.h"
> @@ -45,6 +46,7 @@
>   #include "system/runstate.h"
>   #include "exec/replay-core.h"
>   #include "exec/hwaddr.h"
> +#include "exec/memop.h"
>   
>   #include "internals.h"
>   
> @@ -551,6 +553,26 @@ static int gdb_write_register(CPUState *cpu, uint8_t *mem_buf, int reg)
>       return 0;
>   }
>   
> +/*
> + * Target helper function to read value into GByteArray, target
> + * supplies the size and target endianess via the MemOp.
> + */
> +int gdb_get_register_value(MemOp op, GByteArray *buf, uint8_t *val)
> +{
> +    size_t bytes = memop_size(op);
> +
> +    if (op & MO_BSWAP) {
> +        for ( int i = bytes ; i > 0; i--) {

memop_size() returns unsigned, but bytes is size_t and i is int, and 
this function returns int. Let's keep them consistent.

There is an extra whitespace between "(" and "int".

Regards,
Akihiko Odaki

> +            g_byte_array_append(buf, &val[i - 1], 1);
> +        };
> +    } else {
> +        g_byte_array_append(buf, val, bytes);
> +    }
> +
> +    return bytes;
> +}
> +
> +
>   static void gdb_register_feature(CPUState *cpu, int base_reg,
>                                    gdb_get_reg_cb get_reg, gdb_set_reg_cb set_reg,
>                                    const GDBFeature *feature)