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From: Lv Ying <lvying.system.thoughts@gmail.com>
To: kernelnewbies@kernelnewbies.org
Subject: Why does dump_stack need asmlinkage?
Date: Wed, 14 Apr 2021 07:54:35 -0700	[thread overview]
Message-ID: <20210414145422.GA33226@localhost.localdomain> (raw)

Hi all:

asmlinkage is only defined in arch ia64 and x86_32:
1. arch/x86/include/asm/linkage.h:
#ifdef CONFIG_X86_32
#define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
#endif /* CONFIG_X86_32 */

2. arch/ia64/include/asm/linkage.h:
#define asmlinkage CPP_ASMLINKAGE __attribute__((syscall_linkage))

3. arch independent include/linux/linkage.h:
#ifdef __cplusplus
#define CPP_ASMLINKAGE extern "C"
#else
#define CPP_ASMLINKAGE
#endif

#ifndef asmlinkage
#define asmlinkage CPP_ASMLINKAGE
#endif

As kernelnewbies FAQ(https://kernelnewbies.org/FAQ/asmlinkage) said, in short, asmlinkage tells your compiler to look on the CPU stack for the function parameters, instead of registers.

So, there are two questions:
1. asmlinkage is only defined in x86_32 and ia64, what about other archs? How do they achieve the same effect as mentioned above?
2. "asmlinkage __visible void dump_stack(void)", dump_stack does not have any parameter, so why do it need asmlinkage?

Thanks!
Lv Ying

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                 reply	other threads:[~2021-04-14 14:56 UTC|newest]

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