On Tue, 15 Dec 2015 17:10:57 -0800
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Dec 15, 2015 at 1:11 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> >
> > Hold off. I reread what Linus wrote, and it should only do the copy if
> > it actually changed something.
Here's v2.
>
> Right. Please just write the new copy out at the end, and make the
> original file open be read-only.
It was a bit more invasive than I liked, because the writes would also
append to the file. Luckily, all writes and lseeks are called by
wrappers, so I modified the wrappers to not write to the file but
instead move the pointer within the mmaped file and only write to
memory. If the write was passed the end of the file, it would allocate
memory memory and write to that instead.
>
> Also, the "good" way to rewrite files is not to unlink and create a
> new file with the same name on top, but to create a new file with a
> new name, and then rename on top of the file. That way you never get
> half-way done files when somebody ^C's in the middle, but all or
> nothing.
Yep, I understand that pain.
Now when the file is all done, if a write was called at all, it would
create a new file (appended with ".rc") and then rename() it over the old one.
Compiled and Boot tested but still needs to go through my other tests.
Once again, this patch is added on top of Russell's patch.
Russell, can you try this one on top of yours.
-- Steve
diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 038a11aa0865..a0abc67f0f44 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -48,12 +48,17 @@
static int fd_map; /* File descriptor for file being modified. */
static int mmap_failed; /* Boolean flag. */
-static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
static char gpfx; /* prefix for global symbol name (sometimes '_') */
static struct stat sb; /* Remember .st_size, etc. */
static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
static const char *altmcount; /* alternate mcount symbol name */
static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
+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 */
/* setjmp() return values */
enum {
@@ -67,10 +72,14 @@ static void
cleanup(void)
{
if (!mmap_failed)
- munmap(ehdr_curr, sb.st_size);
+ munmap(file_map, sb.st_size);
else
- free(ehdr_curr);
- close(fd_map);
+ free(file_map);
+ file_map = NULL;
+ free(file_append);
+ file_append = NULL;
+ file_append_size = 0;
+ file_updated = 0;
}
static void __attribute__((noreturn))
@@ -92,12 +101,22 @@ succeed_file(void)
static off_t
ulseek(int const fd, off_t const offset, int const whence)
{
- off_t const w = lseek(fd, offset, whence);
- if (w == (off_t)-1) {
- perror("lseek");
+ switch (whence) {
+ case SEEK_SET:
+ file_ptr = file_map + offset;
+ break;
+ case SEEK_CUR:
+ file_ptr += offset;
+ break;
+ case SEEK_END:
+ file_ptr = file_map + (sb.st_size - offset);
+ break;
+ }
+ if (file_ptr < file_map) {
+ fprintf(stderr, "lseek: seek before file\n");
fail_file();
}
- return w;
+ return file_ptr - file_map;
}
static size_t
@@ -114,12 +133,38 @@ uread(int const fd, void *const buf, size_t const count)
static size_t
uwrite(int const fd, void const *const buf, size_t const count)
{
- size_t const n = write(fd, buf, count);
- if (n != count) {
- perror("write");
- fail_file();
+ size_t cnt = count;
+ off_t idx = 0;
+
+ file_updated = 1;
+
+ if (file_ptr + count >= file_end) {
+ off_t aoffset = (file_ptr + count) - file_end;
+
+ if (aoffset > file_append_size) {
+ file_append = realloc(file_append, aoffset);
+ file_append_size = aoffset;
+ }
+ if (!file_append) {
+ perror("write");
+ fail_file();
+ }
+ if (file_ptr < file_end) {
+ cnt = file_end - file_ptr;
+ } else {
+ cnt = 0;
+ idx = aoffset - count;
+ }
}
- return n;
+
+ if (cnt)
+ memcpy(file_ptr, buf, cnt);
+
+ if (cnt < count)
+ memcpy(file_append + idx, buf, count - cnt);
+
+ file_ptr += count;
+ return count;
}
static void *
@@ -192,9 +237,7 @@ static int make_nop_arm64(void *map, size_t const offset)
*/
static void *mmap_file(char const *fname)
{
- void *addr;
-
- fd_map = open(fname, O_RDWR);
+ fd_map = open(fname, O_RDONLY);
if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
perror(fname);
fail_file();
@@ -203,33 +246,58 @@ static void *mmap_file(char const *fname)
fprintf(stderr, "not a regular file: %s\n", fname);
fail_file();
}
- addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
- fd_map, 0);
+ file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
+ fd_map, 0);
mmap_failed = 0;
- if (addr == MAP_FAILED) {
+ if (file_map == MAP_FAILED) {
mmap_failed = 1;
- addr = umalloc(sb.st_size);
- uread(fd_map, addr, sb.st_size);
+ file_map = umalloc(sb.st_size);
+ uread(fd_map, file_map, sb.st_size);
}
-
- /*
- * After reading the entire file into memory, delete it
- * and write it back, to prevent weird side effects of modifying
- * an object file in place.
- */
close(fd_map);
- if (unlink(fname) < 0) {
- perror(fname);
- fail_file();
- }
- fd_map = open(fname, O_RDWR | O_CREAT, sb.st_mode);
- if (fd_map < 0) {
- perror(fname);
- fail_file();
- }
- uwrite(fd_map, addr, sb.st_size);
- return addr;
+ file_end = file_map + sb.st_size;
+
+ return file_map;
+}
+
+static void write_file(const char *fname)
+{
+ char tmp_file[strlen(fname) + 4];
+ size_t n;
+
+ if (file_updated) {
+ snprintf(tmp_file, "%s.rc", fname);
+
+ /*
+ * After reading the entire file into memory, delete it
+ * and write it back, to prevent weird side effects of modifying
+ * an object file in place.
+ */
+ fd_map = open(tmp_file, O_WRONLY | O_CREAT, sb.st_mode);
+ if (fd_map < 0) {
+ perror(fname);
+ fail_file();
+ }
+ n = write(fd_map, file_map, sb.st_size);
+ if (n != sb.st_size) {
+ perror("write");
+ fail_file();
+ }
+ if (file_append_size) {
+ n = write(fd_map, file_append, file_append_size);
+ if (n != file_append_size) {
+ perror("write");
+ fail_file();
+ }
+ }
+ close(fd_map);
+ if (rename(tmp_file, fname) < 0) {
+ perror(fname);
+ fail_file();
+ }
+ }
+
}
/* w8rev, w8nat, ...: Handle endianness. */
@@ -336,7 +404,6 @@ do_file(char const *const fname)
Elf32_Ehdr *const ehdr = mmap_file(fname);
unsigned int reltype = 0;
- ehdr_curr = ehdr;
w = w4nat;
w2 = w2nat;
w8 = w8nat;
@@ -459,6 +526,7 @@ do_file(char const *const fname)
}
} /* end switch */
+ write_file(fname);
cleanup();
}
@@ -511,11 +579,14 @@ main(int argc, char *argv[])
case SJ_SETJMP: /* normal sequence */
/* Avoid problems if early cleanup() */
fd_map = -1;
- ehdr_curr = NULL;
mmap_failed = 1;
+ file_map = NULL;
+ file_ptr = NULL;
+ file_updated = 0;
do_file(file);
break;
case SJ_FAIL: /* error in do_file or below */
+ sprintf("%s: failed\n", file);
++n_error;
break;
case SJ_SUCCEED: /* premature success */
--
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