file_write_read.c: move from cpp-cheat

Improve README C section with example tree.

README.adoc

@@ -11659,6 +11659,8 @@ One "downside" of glibc is that it exercises much more kernel functionality on i
 
 This section contains userland content, such as <<c>>, <<cpp>> and <<posix>> examples.
 
+Userland assembly content is located at: <<userland-assembly>>. It was split from this section basically becase we were hitting the HTML `h6` limit, stupid web :-)
+
 This content makes up the bulk of the link:userland/[] directory.
 
 Getting started at: <<userland-setup>>
@@ -11671,14 +11673,30 @@ This section was originally moved in here from: https://github.com/cirosantilli/
 
 Programs under link:userland/c/[] are examples of link:https://en.wikipedia.org/wiki/ANSI_C[ANSI C] programming:
 
+* link:userland/c/hello.c[]
+* main` and environment
+** link:userland/c/return0.c[]
+** link:userland/c/return1.c[]
+** link:userland/c/return2.c[]
+** link:userland/c/exit0.c[]
+** link:userland/c/exit1.c[]
+** link:userland/c/exit2.c[]
+** link:userland/c/print_argv.c[]
 * Standard library
-** assert.h
+** `assert.h`
 *** link:userland/c/assert_fail.c[]
 ** `stdlib.h`
-*** Exit related
+*** exit
 **** link:userland/c/abort.c[]
-
-Userland assembly content is located at: <<userland-assembly>>. It was split from this section basically becase we were hitting the HTML `h6` limit, stupid web :-)
+*** malloc
+**** link:userland/c/out_of_memory.c[]
+** `stdio.h`
+*** link:userland/c/stderr.c[]
+*** link:userland/c/getchar.c[]
+*** File IO
+**** link:userland/c/file_write_read.c[]
+* Fun
+** link:userland/c/infinite_loop.c[]
 
 ==== GCC C extensions
 
@@ -13084,7 +13102,7 @@ Note how Sn is weirdly packed inside Dn, and Dn weirdly packed inside Qn, likely
 
 And you can't access the higher bytes at D16 or greater with Sn.
 
-===== ARM vadd instruction
+===== ARM VADD instruction
 
 * link:userland/arch/arm/vadd_scalar.S[]: see also: <<floating-point-assembly>>
 * link:userland/arch/arm/vadd_vector.S[]: see also: <<simd-assembly>>
@@ -13203,20 +13221,20 @@ link:userland/arch/aarch64/add_vector.S[]
 
 Good first instruction to learn SIMD: <<simd-assembly>>
 
-===== ARMv8 aarch64 fadd instruction
+===== ARMv8 aarch64 FADD instruction
 
 * link:userland/arch/aarch64/fadd_vector.S[]: see also: <<simd-assembly>>
 * link:userland/arch/aarch64/fadd_scalar.S[]: see also: <<floating-point-assembly>>
 
-====== ARM fadd vs vadd
+====== ARM FADD vs VADD
 
 It is very confusing, but `fadds` and `faddd` in Aarch32 are <<gnu-gas-assembler-arm-unified-syntax,pre-UAL>> for `vadd.f32` and `vadd.f64` which we use in this tutorial: <<arm-vadd-instruction>>
 
 The same goes for most ARMv7 mnemonics: `f*` is old, and `v*` is the newer better syntax.
 
-But then, in ARMv8, they decided to use <<armv8-aarch64-fadd-instruction>> as the main floating point add name, and get rid of `vadd`!
+But then, in ARMv8, they decided to use <<armv8-aarch64-fadd-instruction>> as the main floating point add name, and get rid of VADD!
 
-Also keep in mind that fused multiply add is `fmadd`.
+Also keep in mind that fused multiply add is FMADD.
 
 Examples at: <<simd-assembly>>
 

lkmc.h

@@ -4,6 +4,7 @@
 #define LKMC_H
 
 #if !defined(__ASSEMBLER__)
+#include <errno.h>
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdint.h>
@@ -20,6 +21,15 @@ LKMC_ASSERT_EQ_DECLARE(32);
 LKMC_ASSERT_EQ_DECLARE(64);
 void lkmc_assert_fail(uint32_t line);
 void lkmc_assert_memcmp(const void *s1, const void *s2, size_t n, uint32_t line);
+
+#define LKMC_ARRAY_SIZE(array) (sizeof(array)/sizeof(array[0]))
+/* Standard action to take in case of a file IO error. */
+#define LKMC_IO_ERROR(function, path) \
+    fprintf(stderr, "error: %s errno = %d, path = %s\n", function, errno, path); \
+    exit(EXIT_FAILURE);
+#define LKMC_TMP_EXT ".tmp"
+#define LKMC_TMP_FILE __FILE__ LKMC_TMP_EXT
+#define LKMC_TMP_FILE_NAMED(name) __FILE__ "__" name LKMC_TMP_EXT
 #endif
 
 /* Assert that the given branch instruction is taken. */

path_properties.py

@@ -430,6 +430,7 @@ path_properties_tuples = (
                         'exit1.c': {'exit_status': 1},
                         'exit2.c': {'exit_status': 2},
                         'false.c': {'exit_status': 1},
+                        'file_write_read.c': {'baremetal': False},
                         'getchar.c': {'interactive': True},
                         'infinite_loop.c': {'more_than_1s': True},
                         'out_of_memory.c': {'disrupts_system': True},

userland/arch/x86_64/dec.S

@@ -5,5 +5,5 @@
 LKMC_PROLOGUE
     mov $3, %rax
     dec %rax
-    LKMC_ASSERT_EQ_32(%rax, $2)
+    LKMC_ASSERT_EQ(%rax, $2)
 LKMC_EPILOGUE

userland/c/file_write_read.c

@@ -0,0 +1,136 @@
+#include <lkmc.h>
+
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+
+/* Returns the size of the given open `FILE*`.
+ *
+ * If an error occurs, returns `-1L`.
+ *
+ * Does not work for pipes.
+ */
+long fget_file_size(FILE *fp) {
+    long oldpos;
+    long return_value;
+    oldpos = ftell(fp);
+    if (oldpos == -1L) {
+        return -1L;
+    }
+    if (fseek(fp, 0, SEEK_END) != 0) {
+        return -1L;
+    }
+    return_value = ftell(fp);
+    if (return_value == -1L) {
+        return -1L;
+    }
+    /* Restore the old position. */
+    if (fseek(fp, oldpos , SEEK_SET) != 0) {
+        return -1L;
+    }
+    return return_value;
+}
+
+/* Same as `file_size`, but takes the path instead of a `FILE*`. */
+long file_size(char *path) {
+    FILE *fp;
+    long return_value;
+    fp = fopen(path, "r");
+    if (fp == NULL) {
+        return -1L;
+    }
+    return_value = fget_file_size(fp);
+    if (fclose(fp) == EOF) {
+        return -1L;
+    }
+    return return_value;
+}
+
+/* Read the entire file to a char[] dynamically allocated inside this function.
+ *
+ * Returns a pointer to the start of that array.
+ *
+ * In case of any error, returns NULL.
+ *
+ * http://stackoverflow.com/questions/174531/easiest-way-to-get-files-contents-in-c
+ */
+char *file_read(char *path) {
+    FILE *fp;
+    char *buffer;
+    long fsize;
+
+    fp = fopen(path , "rb");
+    if (fp == NULL) {
+        return NULL;
+    }
+    fsize = fget_file_size(fp);
+    if (fsize < 0){
+        fprintf(stderr, "could not determine lenght of:\n%s\n", path);
+        return NULL;
+    }
+    buffer = (char*)malloc(fsize);
+    if (buffer == NULL) {
+        return NULL;
+    }
+    if (fread(buffer, 1, fsize, fp) != (size_t)fsize) {
+        return NULL;
+    }
+    if (fclose(fp) == EOF){
+        return NULL;
+    }
+    return buffer;
+}
+
+/* Write a null terminated string to file
+ *
+ * Return -1 on failure, 0 on success.
+ */
+int file_write(char *path, char *write_string) {
+    long len;
+    FILE *fp;
+
+    fp = fopen(path, "wb");
+    if (fp == NULL) {
+        return -1;
+    }
+    len = strlen(write_string);
+    /* copy the file into the buffer: */
+    if (fwrite(write_string, 1, len, fp) != (size_t)len) {
+        return -1;
+    }
+    if (fclose(fp) == EOF) {
+        return -1;
+    }
+    return 0;
+}
+
+int main(void) {
+    char *path = LKMC_TMP_FILE;
+    char *input = "asdf\nqwer\n";
+
+    /* Write entire string to file at once. */
+    if (file_write(path, input) == -1) {
+        LKMC_IO_ERROR("file_write", path);
+    }
+
+    /* Read entire file at once to a string. */
+    {
+        char *output = file_read(path);
+        if (output == NULL) {
+            LKMC_IO_ERROR("file_read", path);
+        }
+        assert(strcmp(input, output) == 0);
+        free(output);
+    }
+
+    /* Get file size. */
+    {
+        long size = file_size(path);
+        if (size == -1) {
+            LKMC_IO_ERROR("file_size", path);
+        }
+        assert((size_t)size == strlen(input));
+    }
+
+    return EXIT_SUCCESS;
+}

userland/c/infinite_loop.c

@@ -1,4 +1,6 @@
-/* Loop infinitely. Print an integer whenever a period is reached:
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#c
+ *
+ * Loop infinitely. Print an integer whenever a period is reached:
  *
  * ....
  * ./infinite_loop [period]