Ports/gdb: Use mmap instead of malloc for sigaltstack()

Stack regions can't be made volatile, which makes it impossible for malloc to manage memory that's used for `sigaltstack()`. Let's use mmap instead. Co-authored-by: Idan Horowitz <idan.horowitz@gmail.com>
Author: https://github.com/BertalanD Commit: https://github.com/SerenityOS/serenity/commit/9f2e8683de4 Pull-request: https://github.com/SerenityOS/serenity/pull/11278
2025-01-24 02:03:06 -05:00 · 2021-12-16 19:20:45 +01:00 · 2021-12-16 19:20:45 +01:00 · 9f2e8683de · 2024-07-17 22:00:41 +09:00
commit 9f2e8683de
parent bd3bbd0329
1 changed files with 70 additions and 0 deletions
--- a/Ports/gdb/patches/alt-stack-no-malloc.patch
+++ b/Ports/gdb/patches/alt-stack-no-malloc.patch
@ -0,0 +1,70 @@
+diff --git a/gdbsupport/alt-stack.h b/gdbsupport/alt-stack.h
+index 056ea41..b638533 100644
+--- a/gdbsupport/alt-stack.h
+++ b/gdbsupport/alt-stack.h
+@@ -20,7 +20,9 @@
+ #ifndef GDBSUPPORT_ALT_STACK_H
+ #define GDBSUPPORT_ALT_STACK_H
+ 
+#include "common-defs.h"
+ #include <signal.h>
+#include <sys/mman.h>
+ 
+ namespace gdb
+ {
+@@ -36,31 +38,44 @@ class alternate_signal_stack
+ public:
+   alternate_signal_stack ()
+   {
+    // We can't use xmalloc here on Serenity, because stack regions
+    // do not play well with how malloc manages its memory.
+ #ifdef HAVE_SIGALTSTACK
+-    m_stack.reset ((char *) xmalloc (SIGSTKSZ));
+-
+-    stack_t stack;
+-    stack.ss_sp = m_stack.get ();
+-    stack.ss_size = SIGSTKSZ;
+-    stack.ss_flags = 0;
+-
+-    sigaltstack (&stack, &m_old_stack);
+    void *ptr = mmap (nullptr, SIGSTKSZ, PROT_READ | PROT_WRITE,
+                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (ptr == MAP_FAILED)
+      {
+        warning ("could not mmap alternate signal stack");
+      }
+    else
+      {
+        m_stack = ptr;
+        stack_t stack;
+        stack.ss_sp = m_stack;
+        stack.ss_size = SIGSTKSZ;
+        stack.ss_flags = 0;
+
+        sigaltstack (&stack, &m_old_stack);
+      }
+ #endif
+   }
+ 
+   ~alternate_signal_stack ()
+   {
+ #ifdef HAVE_SIGALTSTACK
+-    sigaltstack (&m_old_stack, nullptr);
+    if (m_stack != nullptr)
+      {
+        sigaltstack (&m_old_stack, nullptr);
+        munmap (m_stack, SIGSTKSZ);
+      }
+ #endif
+   }
+ 
+   DISABLE_COPY_AND_ASSIGN (alternate_signal_stack);
+ 
+ private:
+-
+ #ifdef HAVE_SIGALTSTACK
+-  gdb::unique_xmalloc_ptr<char> m_stack;
+  void *m_stack{ nullptr };
+   stack_t m_old_stack;
+ #endif
+ };