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1 files changed, 39 insertions, 0 deletions

diff --git a/linux/apps/ex4.subx b/linux/apps/ex4.subx
new file mode 100644
index 00000000..3bf62551
--- /dev/null
+++ b/linux/apps/ex4.subx
@@ -0,0 +1,39 @@
+# Read a character from stdin, save it to a global, write it to stdout.
+#
+# To run:
+#   $ bootstrap/bootstrap translate apps/ex4.subx -o ex4
+#   $ bootstrap/bootstrap run ex4
+
+== data
+
+# the global variable we save to
+X:
+    0/imm32  # space for read() to write to
+
+== code
+
+Entry:
+# read(stdin, X, 1)
+# . fd = 0 (stdin)
+bb/copy-to-ebx  0/imm32
+# . data = X (location to write result to)
+b9/copy-to-ecx  X/imm32
+# . size = 1 character
+ba/copy-to-edx  1/imm32
+# . syscall
+e8/call  syscall_read/disp32
+
+# write(stdout, X, 1)
+# . fd = 1 (stdout)
+bb/copy-to-ebx  1/imm32
+# . initialize X (location to read from)
+b9/copy-to-ecx  X/imm32
+# . size = 1 character
+ba/copy-to-edx  1/imm32
+# . syscall
+e8/call  syscall_write/disp32
+
+# exit(ebx)
+e8/call  syscall_exit/disp32
+
+# . . vim:nowrap:textwidth=0