add needstack

Signed-off-by: Mattias Andrée <maandree@member.fsf.org>

3 files changed, 199 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 562d9d4..2393065 100644
--- a/Makefile
+++ b/Makefile
@@ -22,7 +22,7 @@ CCFLAGS_UNHOSTED = -nostdinc -ffreestanding
 
 # Preprocessor flags defined by slibc that are required to build the slibc.
 CCFLAGS_SLIBC_DEFS = -D_SLIBC_SOURCE=1 -D_GNU_SOURCE=1 -D_BSD_SOURCE=1 -D_SLIBC_SUPPRESS_WARNINGS=1 \
-                     -D_POSIX_C_SOURCE=999999L -D_XOPEN_SOURCE=9999 -D__BUILDING_SLIBC=1
+                     -D_POSIX_C_SOURCE=999999L -D_XOPEN_SOURCE=9999 -D_PLAN9_SOURCE=1 -D__BUILDING_SLIBC=1
 # __BUILDING_SLIBC is used to that make all prototypes visible, that are otherwise
 # hidden because the library is compiled with a too old revision of C.
 
diff --git a/include/alloca.h b/include/alloca.h
index d54d18d..49d8879 100644
--- a/include/alloca.h
+++ b/include/alloca.h
@@ -53,6 +53,50 @@ void* alloca(size_t);
 #endif
 
 
+#if defined(__PLAN9_SOURCE)
+/**
+ * Check for execution stack overflow. If the stack of
+ * overflow, or will overflow, the program shall abort.
+ * 
+ * It is possible that the process is killed by SIGSEGV
+ * instead of aborting.
+ * 
+ * This is a Plan 9 from Bell Labs extension.
+ * 
+ * @etymology  I (need) addition (stack) space.
+ * 
+ * @param  n  The number of bytes the stack will grow by.
+ *            0 can be used to check for a current stack
+ *            overflow. Must be non-negative.
+ * 
+ * @since  Always.
+ */
+void (needstack)(int);
+# elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)
+#  define needstack(n)  __needstack(n, __FILE__, __LINE__, __func__)
+# else
+#  define needstack(n)  __needstack(n, __FILE__, __LINE__, NULL)
+# endif
+#endif
+
+
+/**
+ * This function is called if the `needstack` macro is called.
+ * It enhances the `needstack` function with detail on where
+ * the program failed.
+ * 
+ * You should not use this function directly.
+ * 
+ * @param  n     The number of bytes the stack will grow by. 0 can be used
+ *               to check for a current stack overflow. Must be non-negative.
+ * @param  file  The filename of the source cose whence the check was made.
+ * @param  line  The line in the source code whence the check was made.
+ * @param  func  The function in the source code whence the check was made,
+ *               `NULL` if unknown (C99 is required.)
+ */
+void __needstack(int, const char*, int, const char*)
+
+
 
 #endif
 #endif
diff --git a/src/alloca/needstack.c b/src/alloca/needstack.c
new file mode 100644
index 0000000..b75eb02
--- /dev/null
+++ b/src/alloca/needstack.c
@@ -0,0 +1,154 @@
+/**
+ * slibc — Yet another C library
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <slibc/internals.h>
+#include <alloca.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <signal.h>
+
+
+
+/**
+ * Unless the stack can grow with `n` bytes
+ * without overflowing, the program shall
+ * either be killed by the kernel (SIGSEGV)
+ * or this function shall indicate that the
+ * stack cannot be grown.
+ * 
+ * @param   n  The number of bytes the stack must be able to grow.
+ * @return     0 if the stack can grow, 1 otherwise.
+ */
+int stack_will_overflow(intptr_t n)
+{
+  void* prev_brk;
+  
+  /* TODO This function shall block calls to brk and sbrk. */
+  
+  prev_brk = sbrk(n);
+  if (prev_brk == (void*)-1)
+    return 1;
+  if (brk(prev_brk))
+    return 1; /* Should not happen. */
+  
+  {
+    /* TODO This function shall block calls to signal.h functions. */
+    
+    sigset_t old_mask;
+    sigset_t new_mask;
+    void* old_sigsegv_handler;
+    
+    old_sigsegv_handler = signal(SIGSEGV, SIG_DFL);
+    if (old_sigsegv_handler == SIG_ERR)
+      return 1;
+    
+    if (sigprocmask(SIG_UNBLOCK, &new_mask, &old_mask))
+      return 1;
+    
+    (void) alloca((size_t)n);
+    
+    if (sigprocmask(SIG_SETMASK, &old_mask, NULL))
+      return 1;
+    
+    if (signal(SIGSEGV, Sold_sigsegv_handler) == SIG_ERR)
+      return 1;
+  }
+  
+  return 0;
+}
+
+
+/**
+ * Check for execution stack overflow. If the stack of
+ * overflow, or will overflow, the program shall abort.
+ * 
+ * It is possible that the process is killed by SIGSEGV
+ * instead of aborting.
+ * 
+ * This is a Plan 9 from Bell Labs extension.
+ * 
+ * @etymology  I (need) addition (stack) space.
+ * 
+ * @param  n  The number of bytes the stack will grow by.
+ *            0 can be used to check for a current stack
+ *            overflow. Must be non-negative.
+ * 
+ * @since  Always.
+ */
+void (needstack)(int n)
+{
+  int tty;
+  
+  if (stack_will_overflow((intptr_t)n) == 0)
+    return;
+  
+  tty = isatty(STDERR_FILENO);
+  fprintf(stderr,
+	  _("%(\033[00;01m%)%s%(\033[00m%): "
+	    "%(\033[31m%)%s%(\033[00m%)"
+	    "%(: %(\033[31m%)hinted stack growth: %i bytes%(\033[00m%)%)\n"),
+	  tty, program_invocation_name, tty,
+	  tty, (n ? _("imminent stack overflow detected") : _("stack overflow detected")), tty,
+	  n != 0, tty, n, tty);
+  
+  fflush(NULL); /* Flush all streams. */
+  abort();
+}
+
+
+/**
+ * This function is called if the `needstack` macro is called.
+ * It enhances the `needstack` function with detail on where
+ * the program failed.
+ * 
+ * You should not use this function directly.
+ * 
+ * @param  n     The number of bytes the stack will grow by. 0 can be used
+ *               to check for a current stack overflow. Must be non-negative.
+ * @param  file  The filename of the source cose whence the check was made.
+ * @param  line  The line in the source code whence the check was made.
+ * @param  func  The function in the source code whence the check was made,
+ *               `NULL` if unknown (C99 is required.)
+ */
+void __needstack(int n, const char* file, int line, const char* func)
+{
+  int tty;
+  
+  if (stack_will_overflow((intptr_t)n) == 0)
+    return;
+  
+  tty = isatty(STDERR_FILENO);
+  fprintf(stderr,
+	  _("%(\033[00;01m%)%s%(\033[00m%): "
+	    "%(\033[31m%)%s%(\033[00m%) "
+	    "at line %(\033[33m%)%i%(\033[00m%) "
+	    "of file %(\033[35m%)%s%(\033[00m%)"
+	    "%(, function %(\033[1;34m%)%s%(\033[00m%)%)"
+	    "%(: %(\033[31m%)hinted stack growth: %i bytes%(\033[00m%)%)\n"),
+	  tty, program_invocation_name, tty,
+	  tty, (n ? _("imminent stack overflow detected") : _("stack overflow detected")), tty,
+	  tty, line, tty,
+	  tty, file, tty,
+	  func != NULL, tty, func, tty,
+	  n != 0, tty, n, tty);
+  
+  fflush(NULL); /* Flush all streams. */
+  abort();
+}
+