diff options
| -rw-r--r-- | src/tools/miri/src/shims/unix/fd.rs | 28 | ||||
| -rw-r--r-- | src/tools/miri/tests/pass/shims/fs.rs | 4 | ||||
| -rw-r--r-- | src/tools/miri/tests/utils/libc.rs | 5 |
3 files changed, 28 insertions, 9 deletions
diff --git a/src/tools/miri/src/shims/unix/fd.rs b/src/tools/miri/src/shims/unix/fd.rs index e226a55d8b1..9fbecffc55d 100644 --- a/src/tools/miri/src/shims/unix/fd.rs +++ b/src/tools/miri/src/shims/unix/fd.rs @@ -264,11 +264,19 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> { return this.set_last_error_and_return(LibcError("EBADF"), dest); }; + // Handle the zero-sized case. The man page says: + // > If count is zero, read() may detect the errors described below. In the absence of any + // > errors, or if read() does not check for errors, a read() with a count of 0 returns zero + // > and has no other effects. + if count == 0 { + this.write_null(dest)?; + return interp_ok(()); + } // Non-deterministically decide to further reduce the count, simulating a partial read (but - // never to 0, that has different behavior). + // never to 0, that would indicate EOF). let count = if fd.nondet_short_accesses() && count >= 2 && this.machine.rng.get_mut().random() { - count / 2 + count / 2 // since `count` is at least 2, the result is still at least 1 } else { count }; @@ -338,8 +346,20 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> { return this.set_last_error_and_return(LibcError("EBADF"), dest); }; - // Non-deterministically decide to further reduce the count, simulating a partial write (but - // never to 0, that has different behavior). + // Handle the zero-sized case. The man page says: + // > If count is zero and fd refers to a regular file, then write() may return a failure + // > status if one of the errors below is detected. If no errors are detected, or error + // > detection is not performed, 0 is returned without causing any other effect. If count + // > is zero and fd refers to a file other than a regular file, the results are not + // > specified. + if count == 0 { + // For now let's not open the can of worms of what exactly "not specified" could mean... + this.write_null(dest)?; + return interp_ok(()); + } + // Non-deterministically decide to further reduce the count, simulating a partial write. + // We avoid reducing the write size to 0: the docs seem to be entirely fine with that, + // but the standard library is not (https://github.com/rust-lang/rust/issues/145959). let count = if fd.nondet_short_accesses() && count >= 2 && this.machine.rng.get_mut().random() { count / 2 diff --git a/src/tools/miri/tests/pass/shims/fs.rs b/src/tools/miri/tests/pass/shims/fs.rs index e7f11c54704..022dcc5dcba 100644 --- a/src/tools/miri/tests/pass/shims/fs.rs +++ b/src/tools/miri/tests/pass/shims/fs.rs @@ -72,7 +72,9 @@ fn test_file() { // Writing to a file opened for reading should error (and not stop interpretation). std does not // categorize the error so we don't check for details. - file.write(&[]).unwrap_err(); + file.write(&[0]).unwrap_err(); + // However, writing 0 bytes can succeed or fail. + let _ignore = file.write(&[]); // Removing file should succeed. remove_file(&path).unwrap(); diff --git a/src/tools/miri/tests/utils/libc.rs b/src/tools/miri/tests/utils/libc.rs index 1a3cd067c04..4757a5a268c 100644 --- a/src/tools/miri/tests/utils/libc.rs +++ b/src/tools/miri/tests/utils/libc.rs @@ -34,10 +34,7 @@ pub unsafe fn write_all( if res < 0 { return res; } - if res == 0 { - // EOF? - break; - } + // Apparently a return value of 0 is just a short write, nothing special (unlike reads). written_so_far += res as libc::size_t; } return written_so_far as libc::ssize_t; |