我正在手册页中阅读有关信号安全的abort内容，它是 POSIX 标准要求的异步信号安全功能之一。然而，根据abort的手册页，它说
直到 glibc 2.26，如果 abort() 函数导致进程终止，所有打开的流都会被关闭并刷新（与 fclose(3) 一样）。
fclose未列为异步信号安全（尽管close是）。这是否意味着abort2.27 之前的 glibc 版本中异步信号不安全？
我认为这exit(3)不是异步信号安全的另一个原因，因为它会刷新 stdio 缓冲区，这就是abort过去的做法。
fclose未列为异步信号安全（尽管close是）。这是否意味着abort2.27 之前的 glibc 版本中异步信号不安全？
是的，你是对的。abort在早期版本中不是异步信号安全的。在某个阶段，它将[尝试]fclose所有打开的流。并且，它将通过它设置的内部信号处理程序来执行此操作。
给定的流可能被锁定或处于不确定状态。TL;DR 是abort 不异步安全的，因为fclose过去和现在都不是异步安全的。
缺乏异步安全性的原因之一是mallocet。等人。不是异步安全的。尽管它们将访问包装在互斥体中，但它们不屏蔽信号。进程/线程可以set*buf在涉及执行操作的流上执行操作realloc。信号处理程序中的调用可能会损坏堆和/或崩溃。
能够查看较旧的来源可能会有所帮助。这是glibc源页面：
https://www.gnu.org/software/libc/sources.html
在该页面上，我们可以克隆glibcgit 存储库：
git clone https://sourceware.org/git/glibc.git
cd glibc
git checkout master
这将为我们提供一个相当现代的版本。
但是，通过对那里的说明进行轻微更改，我们可以查看早期版本：
git checkout release/2.25/master
然后，如果我们查看stdlib/abort.c，我们会看到：
/* Now close the streams which also flushes the output the user
defined handler might has produced. */
if (stage == 4)
{
++stage;
__fcloseall ();
}
在更高版本中，第 4 阶段缺少调用__fcloseall：
/* Now try to abort using the system specific command. */
if (stage == 4)
{
++stage;
ABORT_INSTRUCTION;
}
这是 [手动] 与当前 2.25 的差异：
--- abort.c 2022-12-11 22:42:33.064470777 -0500
+++ /tmp/abort.c 2022-12-11 22:42:21.106728443 -0500
@@ -1,4 +1,4 @@
-/* Copyright (C) 1991-2017 Free Software Foundation, Inc.
+/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -13,7 +13,7 @@
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
+ <https://www.gnu.org/licenses/>. */
#include <libc-lock.h>
#include <signal.h>
@@ -21,6 +21,7 @@
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
+#include <internal-signals.h>
/* Try to get a machine dependent instruction which will make the
program crash. This is used in case everything else fails. */
@@ -30,11 +31,8 @@
# define ABORT_INSTRUCTION
#endif
-#include <libio/libioP.h>
-#define fflush(s) _IO_flush_all_lockp (0)
-
/* Exported variable to locate abort message in core files etc. */
-struct abort_msg_s *__abort_msg __attribute__ ((nocommon));
+struct abort_msg_s *__abort_msg;
libc_hidden_def (__abort_msg)
/* We must avoid to run in circles. Therefore we remember how far we
@@ -50,32 +48,24 @@
abort (void)
{
struct sigaction act;
- sigset_t sigs;
/* First acquire the lock. */
__libc_lock_lock_recursive (lock);
/* Now it's for sure we are alone. But recursive calls are possible. */
- /* Unlock SIGABRT. */
+ /* Unblock SIGABRT. */
if (stage == 0)
{
++stage;
- if (__sigemptyset (&sigs) == 0 &&
- __sigaddset (&sigs, SIGABRT) == 0)
- __sigprocmask (SIG_UNBLOCK, &sigs, (sigset_t *) NULL);
- }
-
- /* Flush all streams. We cannot close them now because the user
- might have registered a handler for SIGABRT. */
- if (stage == 1)
- {
- ++stage;
- fflush (NULL);
+ internal_sigset_t sigs;
+ internal_sigemptyset (&sigs);
+ internal_sigaddset (&sigs, SIGABRT);
+ internal_sigprocmask (SIG_UNBLOCK, &sigs, NULL);
}
/* Send signal which possibly calls a user handler. */
- if (stage == 2)
+ if (stage == 1)
{
/* This stage is special: we must allow repeated calls of
`abort' when a user defined handler for SIGABRT is installed.
@@ -93,7 +83,7 @@
}
/* There was a handler installed. Now remove it. */
- if (stage == 3)
+ if (stage == 2)
{
++stage;
memset (&act, '\0', sizeof (struct sigaction));
@@ -103,30 +93,22 @@
__sigaction (SIGABRT, &act, NULL);
}
- /* Now close the streams which also flushes the output the user
- defined handler might has produced. */
- if (stage == 4)
- {
- ++stage;
- __fcloseall ();
- }
-
/* Try again. */
- if (stage == 5)
+ if (stage == 3)
{
++stage;
raise (SIGABRT);
}
/* Now try to abort using the system specific command. */
- if (stage == 6)
+ if (stage == 4)
{
++stage;
ABORT_INSTRUCTION;
}
/* If we can't signal ourselves and the abort instruction failed, exit. */
- if (stage == 7)
+ if (stage == 5)
{
++stage;
_exit (127);