Re: [PATCH v3 3/6] syscall.h: introduce syscall_set_nr()

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 28/01/2025 à 10:16, Dmitry V. Levin a écrit :
> Similar to syscall_set_arguments() that complements
> syscall_get_arguments(), introduce syscall_set_nr()
> that complements syscall_get_nr().
> 
> syscall_set_nr() is going to be needed along with
> syscall_set_arguments() on all HAVE_ARCH_TRACEHOOK
> architectures to implement PTRACE_SET_SYSCALL_INFO API.
> 
> Signed-off-by: Dmitry V. Levin <ldv@strace.io>
> Tested-by: Charlie Jenkins <charlie@rivosinc.com>
> Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
>   arch/arc/include/asm/syscall.h        | 11 +++++++++++
>   arch/arm/include/asm/syscall.h        | 24 ++++++++++++++++++++++++
>   arch/arm64/include/asm/syscall.h      | 16 ++++++++++++++++
>   arch/hexagon/include/asm/syscall.h    |  7 +++++++
>   arch/loongarch/include/asm/syscall.h  |  7 +++++++
>   arch/m68k/include/asm/syscall.h       |  7 +++++++
>   arch/microblaze/include/asm/syscall.h |  7 +++++++
>   arch/mips/include/asm/syscall.h       | 14 ++++++++++++++
>   arch/nios2/include/asm/syscall.h      |  5 +++++
>   arch/openrisc/include/asm/syscall.h   |  6 ++++++
>   arch/parisc/include/asm/syscall.h     |  7 +++++++
>   arch/powerpc/include/asm/syscall.h    | 10 ++++++++++
>   arch/riscv/include/asm/syscall.h      |  7 +++++++
>   arch/s390/include/asm/syscall.h       | 12 ++++++++++++
>   arch/sh/include/asm/syscall_32.h      | 12 ++++++++++++
>   arch/sparc/include/asm/syscall.h      | 12 ++++++++++++
>   arch/um/include/asm/syscall-generic.h |  5 +++++
>   arch/x86/include/asm/syscall.h        |  7 +++++++
>   arch/xtensa/include/asm/syscall.h     |  7 +++++++
>   include/asm-generic/syscall.h         | 14 ++++++++++++++
>   20 files changed, 197 insertions(+)
> 

> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
> index 76020b66286b..712daa90e643 100644
> --- a/arch/arm64/include/asm/syscall.h
> +++ b/arch/arm64/include/asm/syscall.h
> @@ -61,6 +61,22 @@ static inline void syscall_set_return_value(struct task_struct *task,
>   	regs->regs[0] = val;
>   }
>   
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->syscallno = nr;
> +	if (nr == -1) {
> +		/*
> +		 * When the syscall number is set to -1, the syscall will be
> +		 * skipped.  In this case the syscall return value has to be
> +		 * set explicitly, otherwise the first syscall argument is
> +		 * returned as the syscall return value.
> +		 */
> +		syscall_set_return_value(task, regs, -ENOSYS, 0);
> +	}
> +}
> +
>   #define SYSCALL_MAX_ARGS 6
>   
>   static inline void syscall_get_arguments(struct task_struct *task,

> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
> index 521f279e6b33..7505dcfed247 100644
> --- a/arch/powerpc/include/asm/syscall.h
> +++ b/arch/powerpc/include/asm/syscall.h
> @@ -39,6 +39,16 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>   		return -1;
>   }
>   
> +static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
> +{
> +	/*
> +	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
> +	 * the target task is stopped for tracing on entering syscall, so
> +	 * there is no need to have the same check syscall_get_nr() has.
> +	 */
> +	regs->gpr[0] = nr;

Doesn't the same as for ARM64 apply here as well ?

> +}
> +
>   static inline void syscall_rollback(struct task_struct *task,
>   				    struct pt_regs *regs)
>   {

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