There are issues with BINUNICODE8 and BINBYTES8 opcodes in pickle.1. Unpickling BINBYTES8 is not implemented in Python implementation.2. Highest 32 bits of 64-bit size are silently ignored in C implementation on 32-bit platforms.3. There are no tests for BINUNICODE8 and BINBYTES8.Proposed patch fixes these issues.

To access an array item, the type of the index variable must be size_t (or a type with the same size), otherwise the compiler produce less efficient machine code:http://www.viva64.com/en/a/0050/=> please keep Py_ssize_t type for i(I didn't check for the specific case of Py_ssize_t: it's signed. Does GCC emit the most efficient machine code for it?)diff -r16c8278c03f6Modules/_pickle.c--- a/Modules/_pickle.c+++ b/Modules/_pickle.c@@ -4606,10 +4606,17 @@ static Py_ssize_t calc_binsize(char *bytes, int nbytes) {     unsigned char *s = (unsigned char *)bytes;-    Py_ssize_t i;+    int i;     size_t x = 0; -    for (i = 0; i < nbytes && (size_t)i < sizeof(size_t); i++) {+    if (nbytes > (int)sizeof(size_t)) {+        for (i = (int)sizeof(size_t); i < nbytes; i++) {+            if (s[i])+                return -1;+        }+        nbytes = (int)sizeof(size_t);+    }Please add a comment here to explain that the first loop check for integer overflow, it's not obvious at the first read.Does the Python implementation of pickle produce BINBYTES8? If not: why not?Note: the patch is probably based on a private Mercurial revision, so it didn't get the [Review] button.

> To access an array item, the type of the index variable must be size_t (or a> type with the same size), otherwise the compiler produce less efficient> machine code:http://www.viva64.com/en/a/0050/> > => please keep Py_ssize_t type for ii is small integer between 0 and 8. I don't think that this article is related. Py_ssize_t is signed, and i is compared with int in a loop. And isn't Viva64 work only with Visual C++?  At least I found statements that can be not correct on platforms not supported by Microsoft.> Please add a comment here to explain that the first loop check for integer> overflow, it's not obvious at the first read.Done.> Does the Python implementation of pickle produce BINBYTES8? If not: why not?Yes, it produces BINBYTES8 on 64-bit platform.> Note: the patch is probably based on a private Mercurial revision, so it> didn't get the [Review] button.Yes, I had made some refactoring for unpickling tests and forgot to push they. Here is rebased patch.

New changesetd4f8316d0860 by Serhiy Storchaka in branch '3.4':Issue#25262. Added support for BINBYTES8 opcode in Python implementation ofhttps://hg.python.org/cpython/rev/d4f8316d0860New changesetda9ad20dd470 by Serhiy Storchaka in branch '3.5':Issue#25262. Added support for BINBYTES8 opcode in Python implementation ofhttps://hg.python.org/cpython/rev/da9ad20dd470New changeset8de1967edfdb by Serhiy Storchaka in branch 'default':Issue#25262. Added support for BINBYTES8 opcode in Python implementation ofhttps://hg.python.org/cpython/rev/8de1967edfdb

Thank you Victor and Antoine for your reviews.