Re: git: 8f23665fed2f - main - pcb.h: mark struct pcb to be preserved

Ideally this should be applied to sys/mips/include/pcb.h when MFCed to stable/13. However, considering that stable/13 EOL is two months away and there wouldn't be breaking change to mips's pcb.h, it should be fine to ignore it.

> On Feb 8, 2026, at 23:18, Konstantin Belousov <kib@FreeBSD.org> wrote:
> 
> The branch main has been updated by kib:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=8f23665fed2fbaf4481359b4d2fcdd7b9feb40e3
> 
> commit 8f23665fed2fbaf4481359b4d2fcdd7b9feb40e3
> Author:     Minsoo Choo <minsoochoo0122@proton.me>
> AuthorDate: 2026-02-06 20:03:53 +0000
> Commit:     Konstantin Belousov <kib@FreeBSD.org>
> CommitDate: 2026-02-09 04:17:16 +0000
> 
>    pcb.h: mark struct pcb to be preserved
> 
>    There are programs that depend on this structure (e.g. kernel debuggers)
>    that breaks when the ABI changes.
> 
>    Signed-off-by:  Minsoo Choo <minsoochoo0122@proton.me>
>    Reviewed by:    kib
>    MFC after:      1 week
>    Differential Revision:  https://reviews.freebsd.org/D55149
> ---
> sys/amd64/include/pcb.h   | 21 +++++++++++----------
> sys/arm/include/pcb.h     |  4 ++++
> sys/arm64/include/pcb.h   |  5 +++++
> sys/i386/include/pcb.h    | 17 +++++++++--------
> sys/powerpc/include/pcb.h |  5 +++++
> sys/riscv/include/pcb.h   |  5 +++++
> 6 files changed, 39 insertions(+), 18 deletions(-)
> 
> diff --git a/sys/amd64/include/pcb.h b/sys/amd64/include/pcb.h
> index 27e1dce08ee1..5a1e8529ad8b 100644
> --- a/sys/amd64/include/pcb.h
> +++ b/sys/amd64/include/pcb.h
> @@ -44,18 +44,19 @@
> 
> #ifdef __amd64__
> /*
> - * NB: The fields marked with (*) are used by kernel debuggers.  Their
> - * ABI should be preserved.
> + * struct pcb is known to and used by kernel debuggers. Its layout must be kept
> + * stable. When adding extra fields that are accessed by kernel debuggers,
> + * debuggers should be backward compatible by using osreldate.
>  */
> struct pcb {
> -	register_t	pcb_r15;	/* (*) */
> -	register_t	pcb_r14;	/* (*) */
> -	register_t	pcb_r13;	/* (*) */
> -	register_t	pcb_r12;	/* (*) */
> -	register_t	pcb_rbp;	/* (*) */
> -	register_t	pcb_rsp;	/* (*) */
> -	register_t	pcb_rbx;	/* (*) */
> -	register_t	pcb_rip;	/* (*) */
> +	register_t	pcb_r15;
> +	register_t	pcb_r14;
> +	register_t	pcb_r13;
> +	register_t	pcb_r12;
> +	register_t	pcb_rbp;
> +	register_t	pcb_rsp;
> +	register_t	pcb_rbx;
> +	register_t	pcb_rip;
> 	register_t	pcb_fsbase;
> 	register_t	pcb_gsbase;
> 	register_t	pcb_kgsbase;
> diff --git a/sys/arm/include/pcb.h b/sys/arm/include/pcb.h
> index fd77544c22c1..810b1e665b19 100644
> --- a/sys/arm/include/pcb.h
> +++ b/sys/arm/include/pcb.h
> @@ -42,6 +42,10 @@
> #include <machine/vfp.h>
> 
> /*
> + * struct pcb is known to and used by kernel debuggers. Its layout must be kept
> + * stable. When adding extra fields that are accessed by kernel debuggers,
> + * debuggers should be backward compatible by using osreldate.
> + *
>  * WARNING!
>  * Keep pcb_regs first for faster access in switch.S
>  */
> diff --git a/sys/arm64/include/pcb.h b/sys/arm64/include/pcb.h
> index c0feb1149cf5..9955f5b22714 100644
> --- a/sys/arm64/include/pcb.h
> +++ b/sys/arm64/include/pcb.h
> @@ -46,6 +46,11 @@ struct trapframe;
> #define	PCB_FP		10
> #define	PCB_LR		11
> 
> +/*
> + * struct pcb is known to and used by kernel debuggers. Its layout must be kept
> + * stable. When adding extra fields that are accessed by kernel debuggers,
> + * debuggers should be backward compatible by using osreldate.
> + */
> struct pcb {
> 	uint64_t	pcb_x[12];
> 	/* These two need to be in order as we access them together */
> diff --git a/sys/i386/include/pcb.h b/sys/i386/include/pcb.h
> index 1b14efa425b5..1385bfeeef31 100644
> --- a/sys/i386/include/pcb.h
> +++ b/sys/i386/include/pcb.h
> @@ -44,16 +44,17 @@
> #include <machine/npx.h>
> 
> /*
> - * NB: The fields marked with (*) are used by kernel debuggers.  Their
> - * ABI should be preserved.
> + * struct pcb is known to and used by kernel debuggers. Its layout must be kept
> + * stable. When adding extra fields that are accessed by kernel debuggers,
> + * debuggers should be backward compatible by using osreldate.
>  */
> struct pcb {
> -	int	pcb_edi;	/* (*) */
> -	int	pcb_esi;	/* (*) */
> -	int	pcb_ebp;	/* (*) */
> -	int	pcb_esp;	/* (*) */
> -	int	pcb_ebx;	/* (*) */
> -	int	pcb_eip;	/* (*) */
> +	int	pcb_edi;
> +	int	pcb_esi;
> +	int	pcb_ebp;
> +	int	pcb_esp;
> +	int	pcb_ebx;
> +	int	pcb_eip;
> 	struct segment_descriptor pcb_fsd;
> 	struct segment_descriptor pcb_gsd;
> 	int	pcb_ds;
> diff --git a/sys/powerpc/include/pcb.h b/sys/powerpc/include/pcb.h
> index 0230cf78aba7..7ebd13dd0ed1 100644
> --- a/sys/powerpc/include/pcb.h
> +++ b/sys/powerpc/include/pcb.h
> @@ -41,6 +41,11 @@
> #include <machine/setjmp.h>
> 
> #ifndef _STANDALONE
> +/*
> + * struct pcb is known to and used by kernel debuggers. Its layout must be kept
> + * stable. When adding extra fields that are accessed by kernel debuggers,
> + * debuggers should be backward compatible by using osreldate.
> + */
> struct pcb {
> 	register_t	pcb_context[20];	/* non-volatile r12-r31 */
> 	register_t	pcb_cr;			/* Condition register */
> diff --git a/sys/riscv/include/pcb.h b/sys/riscv/include/pcb.h
> index bb88516a1385..bcec4c3fd478 100644
> --- a/sys/riscv/include/pcb.h
> +++ b/sys/riscv/include/pcb.h
> @@ -39,6 +39,11 @@
> 
> struct trapframe;
> 
> +/*
> + * struct pcb is known to and used by kernel debuggers. Its layout must be kept
> + * stable. When adding extra fields that are accessed by kernel debuggers,
> + * debuggers should be backward compatible by using osreldate.
> + */
> struct pcb {
> 	uint64_t	pcb_ra;		/* Return address */
> 	uint64_t	pcb_sp;		/* Stack pointer */