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libinterp/comp-386: Fix native compiler for Linux/386

On Linux/386, malloc()ed code cannot be executed. Replace
malloc()/mallocz()/free() with newly defined functions xalloc(),
xallocz(), xfree(), xactivate().

The new functions are implemented using mmap() to allocate executable
pages. Through the use of xactivate(), they also support W/X.

All other 386 platforms define xalloc() as malloc(),
xallocz() as mallocz(..., 0), xfree() as free(), and xactivate()
as NOP for compatibility.

--- a/libinterp/comp-386.c

+++ b/libinterp/comp-386.c

@@ -2,6 +2,7 @@

 #include "isa.h"

 #include "interp.h"

 #include "raise.h"

+#include "xalloc.h"

 #define DOT			((ulong)code)

@@ -1520,7 +1521,7 @@

 	if(comvec)

 		return;

-	comvec = malloc(32);

+	comvec = xalloc(32);

 	if(comvec == nil)

 		error(exNomem);

 	code = (uchar*)comvec;

@@ -1536,6 +1537,7 @@

 	modrm(Ojmprm, O(REG, PC), RTMP, 4);

 	segflush(comvec, 32);

+	xactivate(comvec);

 }

 static void

@@ -1855,7 +1857,7 @@

 	n += code - tmp;

 	free(tmp);

-	code = mallocz(n, 0);

+	code = xallocz(n);

 	if(code == nil)

 		return;

@@ -1869,6 +1871,7 @@

 			(ulong)t, t->size, (ulong)t->initialize, (ulong)t->destroy, n);

 	segflush(t->initialize, n);

+	xactivate(t->initialize);

 }

 static void

@@ -1929,7 +1932,7 @@

 	n = (n+3)&~3;

 	nlit *= sizeof(ulong);

-	base = mallocz(n + nlit, 0);

+	base = xallocz(n + nlit);

 	if(base == nil)

 		goto bad;

@@ -1980,6 +1983,7 @@

 	m->prog = (Inst*)base;

 	m->compiled = 1;

 	segflush(base, n*sizeof(base));

+	xactivate(base);

 	return 1;

 bad:

 	free(patch);

--- a/libinterp/heap.c

+++ b/libinterp/heap.c

@@ -3,6 +3,7 @@

 #include "interp.h"

 #include "pool.h"

 #include "raise.h"

+#include "xalloc.h"

 void	freearray(Heap*, int);

 void	freelist(Heap*, int);

@@ -277,7 +278,7 @@

 	if(t == nil || --t->ref > 0)

 		return;

-	free(t->initialize);

+	xfree(t->initialize);

 	free(t);

 }

--- a/libinterp/load.c

+++ b/libinterp/load.c

@@ -2,6 +2,7 @@

 #include "isa.h"

 #include "interp.h"

 #include "raise.h"

+#include "xalloc.h"

 #include <kernel.h>

 #define	A(r)	*((Array**)(r))

@@ -568,7 +569,7 @@

 		free(m->type);

 	}

 	free(m->name);

-	free(m->prog);

+	xfree(m->prog);

 	free(m->path);

 	free(m->pctab);

 	if(m->ldt != nil){

--- /dev/null

+++ b/libinterp/xalloc.h

@@ -1,0 +1,47 @@

+#ifdef LINUX_386

+#include <sys/mman.h>

+#include <unistd.h>

+

+static void* xalloc(int s)

+{

+	s += sizeof(int); /* For storing the size */

+	void *r = mmap(NULL, s, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

+	if (r != MAP_FAILED) {

+		/* Use first byte to store the size */

+		int *r2 = r;

+		*r2 = s;

+		++r2;

+		r = r2;

+		return r;

+	}

+	return 0;

+}

+

+static void* xallocz(int s)

+{

+	return xalloc(s);

+}

+

+static void xfree(void *p)

+{

+	if (p == NULL)

+		return;

+	int *p2 = p;

+	--p;

+	p = p2;

+	munmap(p, *p2);

+}

+

+static void xactivate(void *p)

+{

+	int *p2 = p;

+	--p2;

+	p = p2;

+	mprotect(p, *p2, PROT_READ | PROT_EXEC);

+}

+#else

+#define xalloc(s) malloc(s)

+#define xallocz(s) mallocz(s, 0)

+#define xfree(p) free(p)

+#define xactivate(p) {}

+#endif /* LINUX_386 */

-- 

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