有没有办法用最新的内核创建vDSO？

Question

我正在尝试使用最新的内核源代码做一个vDSO。我一直在学习本教程，但是我没有在linux-4.20.13/ https://www.linuxjournal.com/content/creating-vdso-colonels-other-chicken?page=0,0 /x86/ vdso中找到像update_vsyscall()和vdso directory这样的函数。我的问题是:有没有一种方法可以使用新的内核代码创建一个虚拟的syscall，比如gettimeofday()？

Answer 1

中的vdso目录

arch/x86/entry/vdso

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/x86/entry/vdso?h=v4.20.13

例如，将函数直接添加到vclock_gettime.c中，重新构建内核，然后重新引导

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index 007b3fe9d727..a49bef48a9dc 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -238,3 +238,8 @@ notrace time_t __vdso_time(time_t *t)
 }
 time_t time(time_t *t)
    __attribute__((weak, alias("__vdso_time")));
+
+notrace int __vdso_add(int x, int y)
+{
+   return x + y;
+}
diff --git a/arch/x86/entry/vdso/vdso.lds.S b/arch/x86/entry/vdso/vdso.lds.S
index d3a2dce4cfa9..4b976c119845 100644
--- a/arch/x86/entry/vdso/vdso.lds.S
+++ b/arch/x86/entry/vdso/vdso.lds.S
@@ -25,6 +25,7 @@ VERSION {
            __vdso_getcpu;
            time;
            __vdso_time;
+           __vdso_add;
    local: *;
    };
 }

在用户模式下编写测试用例

gcc -otest test.c vdso64.so

#include <stdio.h>

extern int __vdso_add(int x, int y);

int main()
{
    printf("vdso_add: %d\n", __vdso_add(1, 3));
    return 0;
}