Merge pull request #2152 from ghaerr/alloca

[libc] Add __stackavail and __alloca for C86

elks/arch/i86/mm/malloc.c

@@ -284,7 +284,6 @@ int sys_sbrk(int increment, segoff_t *pbrk)
     err = verify_area(VERIFY_WRITE, pbrk, sizeof(*pbrk));
     if (err)
         return err;
-    /* FIXME test for brk+increment overflow/underflow here */
     err = set_brk(brk, increment);
     if (err)
         return err;

libc/c86/Makefile

@@ -6,6 +6,7 @@ LIB ?= out.lib
 include $(TOPDIR)/libc/$(COMPILER).inc
 
 OBJS = $(patsubst %.s,%.ocj,$(wildcard *.s))
+OBJS += stackavail.o
 
 all: $(LIB)
 

libc/c86/c86lib.s

@@ -12,13 +12,26 @@
 ;
 ; C86 helper functions
 ;
-        .global __alloca
-__alloca:
+        .global ___alloca
+        .comm   ___stacklow,2   ; lowest protected SP value
+___alloca:
         pop     bx              ; ret address
         pop     ax              ; alloca size
+        inc     ax
+        and     ax,#0xfffe
+        mov     dx,ax           ; DX = size
+        mov     ax,sp
+        sub     ax,[___stacklow] ; AX = remaining
+        cmp     ax,#0           ; fail if remaining < 0
+        jc      .1
+        cmp     ax,dx           ; fail if remaining < size
+        jc      .1
+        mov     ax,dx           ; OK to extend stack
         sub     sp,ax
         mov     ax,sp           ; AX = mem
         jmp     bx              ; return (compiler won't readjust stack)
+.1:     xor     ax,ax
+        jmp     bx
 
         .global stackcheck
 stackcheck:

libc/c86/stackavail.c

@@ -0,0 +1,12 @@
+#include <alloca.h>
+/* C86 stack checking helper routines */
+
+/* Return true if stack can be extended by size bytes */
+int __stackavail(unsigned int size)
+{
+    unsigned int remaining = (unsigned)&size - __stacklow;
+
+    if ((int)remaining >= 0 && remaining >= size)
+        return 1;
+    return 0;
+}

libc/include/alloca.h

@@ -1,19 +1,17 @@
 #ifndef __ALLOCA_H
 #define __ALLOCA_H
 /*
- * Stack-checking alloca for GCC and OWC
+ * Stack-checking alloca for GCC, OWC and C86
  */
 
-// void *alloca(size_t);
-
-int __stackavail(unsigned int size);
+int __stackavail(unsigned int size);    /* return 1 if size bytes stack available */
+extern unsigned int __stacklow;         /* lowest protected SP value */
 
+#ifdef __GNUC__
 #define alloca(s)           (__stackavail(__ALLOCA_ALIGN(s))?   \
                                  __alloca(__ALLOCA_ALIGN(s)): (void *)0)
-
 #define __ALLOCA_ALIGN(s)   (((s)+(sizeof(int)-1))&~(sizeof(int)-1))
 
-#ifdef __GNUC__
 /* The compiler alloca auto-aligns the stack from the parameter somewhat strangely:
  * 0 -> 0, 1 -> 2, 2 -> 4, 3 -> 4, 4 -> 6 etc.
  * Thus, __stackavail should check for two more bytes available than asked for.
@@ -22,6 +20,10 @@ int __stackavail(unsigned int size);
 #endif
 
 #ifdef __WATCOMC__
+#define alloca(s)           (__stackavail(__ALLOCA_ALIGN(s))?   \
+                                 __alloca(__ALLOCA_ALIGN(s)): (void *)0)
+#define __ALLOCA_ALIGN(s)   (((s)+(sizeof(int)-1))&~(sizeof(int)-1))
+
 #pragma aux __stackavail "*" __modify __nomemory
 
 extern void __based(__segname("_STACK")) *__alloca(unsigned int __size);
@@ -32,4 +34,9 @@ extern void __based(__segname("_STACK")) *__alloca(unsigned int __size);
     __modify __exact __nomemory [__sp]
 #endif
 
+#ifdef __C86__
+void *__alloca(size_t);
+#define alloca(s)           __alloca(s)
+#endif
+
 #endif

libc/watcom/syscall/crt0.c

@@ -44,7 +44,7 @@ int __argc;
 char **__argv;
 char *__program_filename;
 char **environ;
-unsigned int __stacklow;        /* lowest valid SP value */
+unsigned int __stacklow;        /* lowest protected SP value */
 unsigned char _HShift = 12;     /* huge pointer support required by pia.asm */
 
 #if defined(__SMALL__) || defined(__MEDIUM__)   /* near data models */