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Message-ID: <284bc1ed837f0994114534ae7e3d4f6cc0d64f4e.camel@physik.fu-berlin.de>
Date: Wed, 29 Jan 2025 19:32:11 +0100
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Ivan Kokshaysky <ink@...een.parts>, Richard Henderson
<richard.henderson@...aro.org>, Matt Turner <mattst88@...il.com>, Oleg
Nesterov <oleg@...hat.com>, Al Viro <viro@...iv.linux.org.uk>, Arnd
Bergmann <arnd@...db.de>, "Paul E. McKenney" <paulmck@...nel.org>
Cc: "Maciej W. Rozycki" <macro@...am.me.uk>, Magnus Lindholm
<linmag7@...il.com>, linux-alpha@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] alpha/uapi: do not expose kernel-only stack frame
structures
Hi Ivan,
On Wed, 2025-01-29 at 10:43 +0100, Ivan Kokshaysky wrote:
> Parts of asm/ptrace.h went into UAPI with commit 96433f6ee490
> ("UAPI: (Scripted) Disintegrate arch/alpha/include/asm") back in 2012.
> At first glance it looked correct, as many other architectures expose
> 'struct pt_regs' for ptrace(2) PTRACE_GETREGS/PTRACE_SETREGS requests.
> On Alpha, however, these requests have never been implemented;
> 'struct pt_regs' describes internal kernel stack frame which has
> nothing to do with userspace. Same applies to 'struct switch_stack',
> as PTRACE_GETFPREG/PTRACE_SETFPREG are not implemented either.
>
> Move this stuff back into internal asm, where we can ajust it
> without causing a lot of confusion about possible UAPI breakage.
>
> Fixes: 96433f6ee490 ("UAPI: (Scripted) Disintegrate arch/alpha/include/asm")
> Signed-off-by: Ivan Kokshaysky <ink@...een.parts>
> ---
> arch/alpha/include/asm/ptrace.h | 62 +++++++++++++++++++++++++-
> arch/alpha/include/uapi/asm/ptrace.h | 66 +---------------------------
> 2 files changed, 62 insertions(+), 66 deletions(-)
>
> diff --git a/arch/alpha/include/asm/ptrace.h b/arch/alpha/include/asm/ptrace.h
> index 3557ce64ed21..693d4c5b4dc7 100644
> --- a/arch/alpha/include/asm/ptrace.h
> +++ b/arch/alpha/include/asm/ptrace.h
> @@ -2,8 +2,68 @@
> #ifndef _ASMAXP_PTRACE_H
> #define _ASMAXP_PTRACE_H
>
> -#include <uapi/asm/ptrace.h>
> +/*
> + * This struct defines the way the registers are stored on the
> + * kernel stack during a system call or other kernel entry
> + *
> + * NOTE! I want to minimize the overhead of system calls, so this
> + * struct has as little information as possible. It does not have
> + *
> + * - floating point regs: the kernel doesn't change those
> + * - r9-15: saved by the C compiler
> + *
> + * This makes "fork()" and "exec()" a bit more complex, but should
> + * give us low system call latency.
> + */
>
> +struct pt_regs {
> + unsigned long r0;
> + unsigned long r1;
> + unsigned long r2;
> + unsigned long r3;
> + unsigned long r4;
> + unsigned long r5;
> + unsigned long r6;
> + unsigned long r7;
> + unsigned long r8;
> + unsigned long r19;
> + unsigned long r20;
> + unsigned long r21;
> + unsigned long r22;
> + unsigned long r23;
> + unsigned long r24;
> + unsigned long r25;
> + unsigned long r26;
> + unsigned long r27;
> + unsigned long r28;
> + unsigned long hae;
> +/* JRP - These are the values provided to a0-a2 by PALcode */
> + unsigned long trap_a0;
> + unsigned long trap_a1;
> + unsigned long trap_a2;
> +/* These are saved by PAL-code: */
> + unsigned long ps;
> + unsigned long pc;
> + unsigned long gp;
> + unsigned long r16;
> + unsigned long r17;
> + unsigned long r18;
> +};
> +
> +/*
> + * This is the extended stack used by signal handlers and the context
> + * switcher: it's pushed after the normal "struct pt_regs".
> + */
> +struct switch_stack {
> + unsigned long r9;
> + unsigned long r10;
> + unsigned long r11;
> + unsigned long r12;
> + unsigned long r13;
> + unsigned long r14;
> + unsigned long r15;
> + unsigned long r26;
> +};
>
> #define arch_has_single_step() (1)
> #define user_mode(regs) (((regs)->ps & 8) != 0)
> diff --git a/arch/alpha/include/uapi/asm/ptrace.h b/arch/alpha/include/uapi/asm/ptrace.h
> index 5ca45934fcbb..2c08d74deac5 100644
> --- a/arch/alpha/include/uapi/asm/ptrace.h
> +++ b/arch/alpha/include/uapi/asm/ptrace.h
> @@ -2,72 +2,8 @@
> #ifndef _UAPI_ASMAXP_PTRACE_H
> #define _UAPI_ASMAXP_PTRACE_H
>
> -
> -/*
> - * This struct defines the way the registers are stored on the
> - * kernel stack during a system call or other kernel entry
> - *
> - * NOTE! I want to minimize the overhead of system calls, so this
> - * struct has as little information as possible. It does not have
> - *
> - * - floating point regs: the kernel doesn't change those
> - * - r9-15: saved by the C compiler
> - *
> - * This makes "fork()" and "exec()" a bit more complex, but should
> - * give us low system call latency.
> - */
> -
> -struct pt_regs {
> - unsigned long r0;
> - unsigned long r1;
> - unsigned long r2;
> - unsigned long r3;
> - unsigned long r4;
> - unsigned long r5;
> - unsigned long r6;
> - unsigned long r7;
> - unsigned long r8;
> - unsigned long r19;
> - unsigned long r20;
> - unsigned long r21;
> - unsigned long r22;
> - unsigned long r23;
> - unsigned long r24;
> - unsigned long r25;
> - unsigned long r26;
> - unsigned long r27;
> - unsigned long r28;
> - unsigned long hae;
> -/* JRP - These are the values provided to a0-a2 by PALcode */
> - unsigned long trap_a0;
> - unsigned long trap_a1;
> - unsigned long trap_a2;
> -/* These are saved by PAL-code: */
> - unsigned long ps;
> - unsigned long pc;
> - unsigned long gp;
> - unsigned long r16;
> - unsigned long r17;
> - unsigned long r18;
> -};
> -
> /*
> - * This is the extended stack used by signal handlers and the context
> - * switcher: it's pushed after the normal "struct pt_regs".
> + * We have nothing to say to userspace.
> */
> -struct switch_stack {
> - unsigned long r9;
> - unsigned long r10;
> - unsigned long r11;
> - unsigned long r12;
> - unsigned long r13;
> - unsigned long r14;
> - unsigned long r15;
> - unsigned long r26;
> -#ifndef __KERNEL__
> - unsigned long fp[32]; /* fp[31] is fpcr */
> -#endif
> -};
> -
>
> #endif /* _UAPI_ASMAXP_PTRACE_H */
This seems to break the build for the bpf tool on alpha:
In file included from libbpf.c:36:
/build/reproducible-path/linux-6.13~rc7/tools/include/uapi/linux/bpf_perf_event.h:14:28: error: field ‘regs’ has incomplete type
14 | bpf_user_pt_regs_t regs;
| ^~~~
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
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