From a4b2c07ff946363bc6465b301e94c0f3bd2f8de7 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Fri, 31 May 2024 15:20:09 -0400
Subject: add __memperm() for checking current memory permissions

---
 mk/__memperm.d     |  9 +++++++++
 mk/all.mk          |  1 +
 mk/deps.mk         |  4 ++++
 src/__memperm.c    | 36 ++++++++++++++++++++++++++++++++++++
 src/_forced/mmap.h |  1 +
 src/_memperm.h     |  9 +++++++++
 6 files changed, 60 insertions(+)
 create mode 100644 mk/__memperm.d
 create mode 100644 src/__memperm.c
 create mode 100644 src/_memperm.h

diff --git a/mk/__memperm.d b/mk/__memperm.d
new file mode 100644
index 00000000..83eff260
--- /dev/null
+++ b/mk/__memperm.d
@@ -0,0 +1,9 @@
+libc_C.0: libc.a(__memperm.o)
+libc.a(__memperm.o): $(OBJDIR)/__memperm.o
+	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
+
+$(OBJDIR)/__memperm.o: src/__memperm.c
+$(OBJDIR)/__memperm.o: src/_memperm.h
+$(OBJDIR)/__memperm.o:
+	@mkdir -p $(@D)
+	$(CC) -c -o $@ $(CFLAGS) src/__memperm.c
diff --git a/mk/all.mk b/mk/all.mk
index dc4370a3..4b6eb27a 100644
--- a/mk/all.mk
+++ b/mk/all.mk
@@ -1,4 +1,5 @@
 include mk/__undefined.d
+include mk/__memperm.d
 include mk/ctan.d
 include mk/catan.d
 include mk/ccos.d
diff --git a/mk/deps.mk b/mk/deps.mk
index c9715488..d60a5357 100644
--- a/mk/deps.mk
+++ b/mk/deps.mk
@@ -6,6 +6,10 @@ all: mk/__undefined.d
 mk/__undefined.d: src/__undefined.c
 	sh mk/deps.sh src/__undefined.c
 
+all: mk/__memperm.d
+mk/__memperm.d: src/__memperm.c
+	sh mk/deps.sh src/__memperm.c
+
 all: mk/ctan.d
 mk/ctan.d: src/complex/ctan.c
 	sh mk/deps.sh src/complex/ctan.c
diff --git a/src/__memperm.c b/src/__memperm.c
new file mode 100644
index 00000000..e3bcd64d
--- /dev/null
+++ b/src/__memperm.c
@@ -0,0 +1,36 @@
+#include <inttypes.h>
+#include <stdio.h>
+#include "_memperm.h"
+
+int __memperm(void *ptr)
+{
+	uintptr_t addr = (uintptr_t)ptr;
+	int ret = PROT_NONE;
+
+	FILE *map = fopen("/proc/self/maps", "r");
+	if (map == NULL) {
+		return -1;
+	}
+
+	while (!feof(map)) {
+		uintmax_t low = 0;
+		uintmax_t high = 0;
+		char perms[5];
+		fscanf(map, "%ju-%ju %4s%*s\n", &low, &high, perms);
+		if (low <= addr && high >= addr) {
+			if (perms[0] == 'r') {
+				ret |= PROT_READ;
+			}
+			if (perms[1] == 'w') {
+				ret |= PROT_WRITE;
+			}
+			if (perms[2] == 'x') {
+				ret |= PROT_EXEC;
+			}
+			break;
+		}
+	}
+
+	fclose(map);
+	return ret;
+}
diff --git a/src/_forced/mmap.h b/src/_forced/mmap.h
index 65c1ef01..24256479 100644
--- a/src/_forced/mmap.h
+++ b/src/_forced/mmap.h
@@ -5,6 +5,7 @@
 #define PROT_NONE 0x0
 #define PROT_READ 0x1
 #define PROT_WRITE 0x2
+#define PROT_EXEC 0x4
 #define MAP_PRIVATE 0x02
 #define MAP_FAILED (void*)(-1)
 #define MAP_ANONYMOUS (0x20)
diff --git a/src/_memperm.h b/src/_memperm.h
new file mode 100644
index 00000000..d32d93f8
--- /dev/null
+++ b/src/_memperm.h
@@ -0,0 +1,9 @@
+#ifndef ___MEMPERM_H__
+#define ___MEMPERM_H__
+
+/* for PROT_READ, PROT_WRITE, and PROT_EXEC */
+#include "_forced/mmap.h"
+
+int __memperm(void *);
+
+#endif
-- 
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