[RFC][PATCH 08/13] recordmcount: Clarify what cleanup() does

Matt Helsley
2019-05-23T00:04:15Z

cleanup() mostly frees/unmaps the malloc'd/privately-mapped
copy of the ELF file recordmcount is working on, which is
set up in mmap_file(). It also deals with positioning within
the pseduo prive-mapping of the file and appending to the ELF
file.

Split into two steps:
mmap_cleanup() for the mapping itself
file_append_cleanup() for allocations storing the
appended ELF data.

Also, move the global variable initializations out of the main,
per-object-file loop and nearer to the alloc/init (mmap_file())
and two cleanup functions so we can more clearly see how they're
related.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
---
scripts/recordmcount.c | 151 ++++++++++++++++++++++-------------------
1 file changed, 81 insertions(+), 70 deletions(-)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 1c8b38c0d7fe..697c567c2517 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -48,21 +48,26 @@ static void *file_map; /* pointer of the mapped file */
static void *file_end; /* pointer to the end of the mapped file */
static int file_updated; /* flag to state file was changed */
static void *file_ptr; /* current file pointer location */
+
static void *file_append; /* added to the end of the file */
static size_t file_append_size; /* how much is added to end of file */

/* Per-file resource cleanup when multiple files. */
-static void cleanup(void)
+static void file_append_cleanup(void)
+{
+ free(file_append);
+ file_append = NULL;
+ file_append_size = 0;
+ file_updated = 0;
+}
+
+static void mmap_cleanup(void)
{
if (!mmap_failed)
munmap(file_map, sb.st_size);
else
free(file_map);
file_map = NULL;
- free(file_append);
- file_append = NULL;
- file_append_size = 0;
- file_updated = 0;
}

/* ulseek, uwrite, ...: Check return value for errors. */
@@ -103,7 +108,8 @@ static ssize_t uwrite(void const *const buf, size_t const count)
}
if (!file_append) {
perror("write");
- cleanup();
+ file_append_cleanup();
+ mmap_cleanup();
return -1;
}
if (file_ptr < file_end) {
@@ -129,12 +135,76 @@ static void * umalloc(size_t size)
void *const addr = malloc(size);
if (addr == 0) {
fprintf(stderr, "malloc failed: %zu bytes\n", size);
- cleanup();
+ file_append_cleanup();
+ mmap_cleanup();
return NULL;
}
return addr;
}

+/*
+ * Get the whole file as a programming convenience in order to avoid
+ * malloc+lseek+read+free of many pieces. If successful, then mmap
+ * avoids copying unused pieces; else just read the whole file.
+ * Open for both read and write; new info will be appended to the file.
+ * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
+ * do not propagate to the file until an explicit overwrite at the last.
+ * This preserves most aspects of consistency (all except .st_size)
+ * for simultaneous readers of the file while we are appending to it.
+ * However, multiple writers still are bad. We choose not to use
+ * locking because it is expensive and the use case of kernel build
+ * makes multiple writers unlikely.
+ */
+static void *mmap_file(char const *fname)
+{
+ /* Avoid problems if early cleanup() */
+ fd_map = -1;
+ mmap_failed = 1;
+ file_map = NULL;
+ file_ptr = NULL;
+ file_updated = 0;
+ sb.st_size = 0;
+
+ fd_map = open(fname, O_RDONLY);
+ if (fd_map < 0) {
+ perror(fname);
+ return NULL;
+ }
+ if (fstat(fd_map, &sb) < 0) {
+ perror(fname);
+ goto out;
+ }
+ if (!S_ISREG(sb.st_mode)) {
+ fprintf(stderr, "not a regular file: %s\n", fname);
+ goto out;
+ }
+ file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
+ fd_map, 0);
+ if (file_map == MAP_FAILED) {
+ mmap_failed = 1;
+ file_map = umalloc(sb.st_size);
+ if (!file_map) {
+ perror(fname);
+ goto out;
+ }
+ if (read(fd_map, file_map, sb.st_size) != sb.st_size) {
+ perror(fname);
+ free(file_map);
+ file_map = NULL;
+ goto out;
+ }
+ } else
+ mmap_failed = 0;
+out:
+ close(fd_map);
+ fd_map = -1;
+
+ file_end = file_map + sb.st_size;
+
+ return file_map;
+}
+
+
static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
static unsigned char *ideal_nop;
@@ -238,61 +308,6 @@ static int make_nop_arm64(void *map, size_t const offset)
return 0;
}

-/*
- * Get the whole file as a programming convenience in order to avoid
- * malloc+lseek+read+free of many pieces. If successful, then mmap
- * avoids copying unused pieces; else just read the whole file.
- * Open for both read and write; new info will be appended to the file.
- * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
- * do not propagate to the file until an explicit overwrite at the last.
- * This preserves most aspects of consistency (all except .st_size)
- * for simultaneous readers of the file while we are appending to it.
- * However, multiple writers still are bad. We choose not to use
- * locking because it is expensive and the use case of kernel build
- * makes multiple writers unlikely.
- */
-static void *mmap_file(char const *fname)
-{
- file_map = NULL;
- sb.st_size = 0;
- fd_map = open(fname, O_RDONLY);
- if (fd_map < 0) {
- perror(fname);
- return NULL;
- }
- if (fstat(fd_map, &sb) < 0) {
- perror(fname);
- goto out;
- }
- if (!S_ISREG(sb.st_mode)) {
- fprintf(stderr, "not a regular file: %s\n", fname);
- goto out;
- }
- file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
- fd_map, 0);
- mmap_failed = 0;
- if (file_map == MAP_FAILED) {
- mmap_failed = 1;
- file_map = umalloc(sb.st_size);
- if (!file_map) {
- perror(fname);
- goto out;
- }
- if (read(fd_map, file_map, sb.st_size) != sb.st_size) {
- perror(fname);
- free(file_map);
- file_map = NULL;
- goto out;
- }
- }
-out:
- close(fd_map);
-
- file_end = file_map + sb.st_size;
-
- return file_map;
-}
-
static int write_file(const char *fname)
{
char tmp_file[strlen(fname) + 4];
@@ -436,10 +451,11 @@ static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)

static int do_file(char const *const fname)
{
- Elf32_Ehdr *const ehdr = mmap_file(fname);
+ Elf32_Ehdr *ehdr;
unsigned int reltype = 0;
int rc = -1;

+ ehdr = mmap_file(fname);
if (!ehdr)
goto out;

@@ -575,7 +591,8 @@ static int do_file(char const *const fname)

rc = write_file(fname);
out:
- cleanup();
+ file_append_cleanup();
+ mmap_cleanup();
return rc;
}

@@ -618,12 +635,6 @@ int main(int argc, char *argv[])
strcmp(file + (len - ftrace_size), ftrace) == 0)
continue;

- /* Avoid problems if early cleanup() */
- fd_map = -1;
- mmap_failed = 1;
- file_map = NULL;
- file_ptr = NULL;
- file_updated = 0;
if (do_file(file)) {
fprintf(stderr, "%s: failed\n", file);
++n_error;
--
2.20.1