Re: [PATCH v2 ] MicroBlaze: Add microblaze_get_next_pcs

Simon Marchi
2025-09-03T17:57:51Z

On 9/2/25 8:27 AM, Gopi Kumar Bulusu wrote:
> From 7f2bacc6fffa6830991da36c2044431237bacba1 Mon Sep 17 00:00:00 2001
> From: Gopi Kumar Bulusu <gopi@sankhya.com>
> Date: Tue, 12 Aug 2025 09:42:48 +0530
> Subject: [PATCH v2] MicroBlaze: Add microblaze_get_next_pcs
>
> This patch enables software single stepping for gdbserver target
>
> * gdb/microblaze-tdep.c: Add microblaze_get_next_pcs
>
> Signed-off-by: David Holsgrove <david.holsgrove@petalogix.com>
> Signed-off-by: Nathan Rossi <nathan.rossi@petalogix.com>
> Signed-off-by: Mahesh Bodapati <mbodapat@xilinx.com>
> Signed-off-by: Gopi Kumar Bulusu <gopi@sankhya.com>
> ---
> gdb/microblaze-tdep.c | 91 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 91 insertions(+)
>
> diff --git a/gdb/microblaze-tdep.c b/gdb/microblaze-tdep.c
> index 7b58220871c..cacec8ba186 100644
> --- a/gdb/microblaze-tdep.c
> +++ b/gdb/microblaze-tdep.c
> @@ -590,6 +590,95 @@ microblaze_stabs_argument_has_addr (struct gdbarch *gdbarch, struct type *type)
> return (type->length () == 16);
> }
>
> +/* Return next pc values : next in sequence and/or branch/return target. */
> +
> +static std::vector<CORE_ADDR>
> +microblaze_get_next_pcs (regcache *regcache)
> +{
> + CORE_ADDR pc = regcache_read_pc (regcache);
> + long insn = microblaze_fetch_instruction (pc);
> +
> + enum microblaze_instr_type insn_type;
> + short delay_slots;
> + bool isunsignednum;
> +
> + /* If the current instruction is an imm, look at the inst after. */
> +
> + get_insn_microblaze (insn, &isunsignednum, &insn_type, &delay_slots);
> +
> + int imm;
> + bool immfound = false;
> +
> + if (insn_type == immediate_inst)
> + {
> + int rd, ra, rb;
> + immfound = true;
> + microblaze_decode_insn (insn, &rd, &ra, &rb, &imm);
> + pc += INST_WORD_SIZE;
> + insn = microblaze_fetch_instruction (pc);
> + get_insn_microblaze (insn, &isunsignednum, &insn_type, &delay_slots);
> + }
> +
> + std::optional<CORE_ADDR> next_pc, branch_or_return_pc;
> +
> + /* Compute next instruction address - skip delay slots if any. */
> +
> + if (insn_type != return_inst)
> + next_pc = pc + INST_WORD_SIZE + (delay_slots * INST_WORD_SIZE);
> +
> + microblaze_debug ("single-step insn_type=0x%x pc=0x%lx insn=0x%lx\n",
> + insn_type, pc, insn);

You shouldn't need the trailing \n. Apply elsewhere too.

> +
> + /* Compute target instruction address for branch or return instruction. */
> + if (insn_type == branch_inst || insn_type == return_inst)
> + {
> + int limm;
> + int lrd, lra, lrb;
> + long ra, rb;
> + bool targetvalid;
> + bool unconditionalbranch;

Declare when first use, where possible (ra and rb).

ra and rb should probably be of the type ULONGEST.

> +
> + microblaze_decode_insn (insn, &lrd, &lra, &lrb, &limm);
> + ra = regcache_raw_get_unsigned (regcache, lra);
> + rb = regcache_raw_get_unsigned (regcache, lrb);
> +
> + branch_or_return_pc = microblaze_get_target_address (insn, immfound,
> + imm, pc, ra, rb, &targetvalid, &unconditionalbranch);

Format like this:

branch_or_return_pc
= microblaze_get_target_address (insn, immfound,
imm, pc, ra, rb, &targetvalid,
&unconditionalbranch);

> +
> + microblaze_debug (
> + "single-step uncondbr=%d targetvalid=%d target=0x%lx\n",
> + unconditionalbranch, targetvalid,
> + branch_or_return_pc.value () );

Format like this:

microblaze_debug ("single-step uncondbr=%d targetvalid=%d target=0x%lx",
unconditionalbranch, targetvalid,
branch_or_return_pc.value ());

> +
> + /* Can't reach next address. */
> + if (unconditionalbranch)
> + next_pc.reset ();
> +
> + /* Can't reach a distinct (not here) target address. */
> + if (! targetvalid || branch_or_return_pc == pc ||
> + (next_pc && (branch_or_return_pc == next_pc)))
> + branch_or_return_pc.reset ();

Format like this:

/* Can't reach a distinct (not here) target address. */
if (!targetvalid
|| branch_or_return_pc == pc
|| (next_pc.has_value () && branch_or_return_pc == next_pc))
branch_or_return_pc.reset ();

> + } /* if (branch or return instruction). */
> +
> + /* Create next_pcs vector to return. */
> +
> + std::vector<CORE_ADDR> next_pcs;
> +
> + if (next_pc)

.has_value ()

> + {
> + next_pcs.push_back (next_pc.value () );

We typically use `*next_pc` to access the value (apply elsewhere too).

Remove the space before closing parenthesis (apply elsewhere too).

> + microblaze_debug ("push_back next_pc(0x%lx)\n", next_pc.value () );
> + }
> +
> + if (branch_or_return_pc)
> + {
> + next_pcs.push_back ( branch_or_return_pc.value () );
> + microblaze_debug ("push_back branch_or_return_pc(0x%lx)\n",
> + branch_or_return_pc.value ());

Align the last line properly.

The patch LGTM with those fixed. Let me know if you need help pushing
the patch.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon