Bug #78878 [Com]: Buffer underflow in bc_shift_addsub

Edit report at https://bugs.php.net/bug.php?id=78878&edit=1 ID: 78878 Comment by: thomas-josef dot riedmaier at siemens dot com Reported by: thomas-josef dot riedmaier at siemens dot com Summary: Buffer underflow in bc_shift_addsub Status: Feedback Type: Bug Package: BC math related Operating System: Windows PHP Version: 7.4.0 Assigned To: cmb Block user comment: N Private report: N New Comment: If you need a test setup in which the bug can be reproduced go to https://developer.microsoft.com/en-us/microsoft-edge/tools/vms/ and download the "IE11 on Win7 (x86)" machine. You need to install VC Redistributables, but then you are good to go. Previous Comments: ------------------------------------------------------------------------ [2019-11-29 07:37:54] thomas-josef dot riedmaier at siemens dot com I digged a little bit into this and it appears to be a system-dependent problem. When running the script with Windows7 SP1 or Windows Server 2016 (1607), the script says "Warning: Use of undefined constant �6483605105519922841849335928742092 - assumed '�6483605105519922841849335928742092'" and crashes. Note the non printable character here. When running the script with Windows 10 (1809), the scipt says "Warning: Use of undefined constant 6483605105519922841849335928742092 - assumed '6483605105519922841849335928742092'" and does not crash. Note that there is no unprintable character here. So it appears to me that depending on the Windows setup, php seem to ignore the '²', or not. If it is not ignored, an access violation occurs. ------------------------------------------------------------------------ [2019-11-28 16:02:31] cmb@php.net I cannot reproduce the access violation (neither with the given code, nor when I replace the ² with 2, nor when I just remove the ²). And neither does the assertion trigger in a debug build for me (it won't trigger in release builds anyway). Could you please fix/clarify the test script? ------------------------------------------------------------------------ [2019-11-28 15:03:45] thomas-josef dot riedmaier at siemens dot com Description: ------------ When executing the test snippet below, a buffer underflow occurs in bc_shift_addsub. I theory, bc_shift_addsub's assert statement would be triggered, but this does not play any role in the official windows release binaries https://windows.php.net/downloads/releases/php-7.4.0-Win32-vc15-x64.zip . Instead, on our test machines, an ACCESS_VIOLATION is triggered. Test script: --------------- <?php print bcmul(²6483605105519922841849335928742092, bcpowmod(2, 65535, -4e-4)); ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=78878&edit=1