[Valgrind-developers] [valgrind] vgdb.c (fork_and_exec_valgrind): Fix off-by-one error write

[Mark W. <ma...@so...>]

https://sourceware.org/git/gitweb.cgi?p=valgrind.git;h=f4fe5faf3d0f45b3824bbb9070232682df52a582

commit f4fe5faf3d0f45b3824bbb9070232682df52a582
Author: Mark Wielaard <ma...@kl...>
Date:   Tue Nov 12 13:23:03 2024 +0100

    vgdb.c (fork_and_exec_valgrind): Fix off-by-one error write
    
    commit 646978d9adc5 ("vgdb: Handle EINTR and EAGAIN more
    consistently") introduced an off-by-one issue trying to write back the
    error from child to parent.
    
    Instead of +1 it should have been +written (which initially is zero).
    
    This is in an "should never happen" path, so hopefully didn't really
    cause issues. But if it did happen the parent would have gotten the
    wrong error code.

Diff:
---
 coregrind/vgdb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/coregrind/vgdb.c b/coregrind/vgdb.c
index d6740aecd4..90e3f15020 100644
--- a/coregrind/vgdb.c
+++ b/coregrind/vgdb.c
@@ -1368,7 +1368,7 @@ int fork_and_exec_valgrind (int argc, char **argv, const char *working_dir,
       // We try to write the result to the parent, but always exit.
       size_t written = 0;
       while (written < sizeof (int)) {
-         ssize_t nrw = write (pipefd[1], ((char *) &err) + 1,
+         ssize_t nrw = write (pipefd[1], ((char *) &err) + written,
                               sizeof (int) - written);
          if (nrw == -1) {
             if (errno == EINTR || errno == EAGAIN)