setcontext（）Valgrind大小为8的无效读取

Question

我目前面临一个非常奇怪的问题。我正在建立一个图书馆并将其链接到我的程序。一切运行正常，没有分段错误（也用gdb进行了检查），但是当我使用Valgrind运行程序时，它会疯狂地用行说：

==11972== Invalid read of size 8
==11972==    at 0x509509C: setcontext (setcontext.S:73)
==11972==    by 0x509764F: ??? (in /lib/x86_64-linux-gnu/libc-2.15.so)
==11972==  Address 0x541f060 is 128 bytes inside a block of size 936 alloc'd
==11972==    at 0x4C2B3F8: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==11972==    by 0x402090: environment_get (env.c:99)
==11972==    by 0x401ED6: environment_new (env.c:36)
==11972==    by 0x40124B: thr_new (thr.c:156)
==11972==    by 0x400EBE: main (itest1.c:31)

但是程序运行正常，setcontext的参数已正确分配，没有问题。我有什么理由担心这些台词吗？

谢谢

Answer 1

推迟了七年才进入线程，但是：我通过确保堆栈至少为SIGSTKSZ来解决此问题。因此，以下代码可以解决这个问题：

#include <valgrind/valgrind.h>

//technically, the below doesn't need to be dynamically allocated, but for demonstration:
ucontext_t context = (ucontext_t*) malloc(sizeof(ucontext_t));

getcontext(&context);
void* stack = malloc(SIGSTKSZ);
VALGRIND_STACK_REGISTER(stack, stack + SIGSTKSZ);
context->uc_stack.ss_sp     = stack;
context->uc_stack.ss_size   = SIGSTKSZ;
context->uc_stack.ss_flags  = 0;
sigemptyset(&context->uc_sigmask);
context->uc_link            = &someOtherContextToGoToAfterwards;
makecontext(context, functionForContextToExecute);

然后，在清理它时，您可以做一些负责任的事情，例如：

VALGRIND_STACK_DEREGISTER(context->uc_stack.ss_sp);
free(context->uc_stack.ss_sp);
free(context).