Commits on Aug 18, 2023

1. Add test file for context functions …

   For now, this just tests stack alignment in a context's entry point
   
   This test shows a problem when building on i386 with `-msse2`, where the
   compiler is allowed use some instructions that move data in and out of
   the xmm0-7 registers, requiring them to be aligned on 16-byte
   boundaries. Because the compiler will generally assume the stack is
   correctly aligned on entering a function, the misalignment will
   propagate through the stack until something uses an instruction that
   requires 16-byte alignment, and we get a segmentation fault.
   
   The misalignment happens because the stack is heap-allocated (and the
   heap allocator provides a properly aligned pointer), but we push the
   argument for the async task onto the stack as we call it, leaving the
   stack 4 bytes below proper alignment.
   
   The test is equally valid on x86_64, but the stack alignment is correct
   there - nothing is pushed onto the stack prior to calling the task
   function, as it's passed in a register.

   

   peadar committed Aug 18, 2023
   Configuration menu

   • View commit details
   • Copy full SHA for 0254de3
   • Browse repository at this point

   Copy the full SHA

   0254de3 View commit details

   Browse the repository at this point in the history

2. Align stack correctly when initializing a context …

   In `my_context_spawn`, assuming the allocated stack pointer is 16-bye
   aligned (as it will be from malloc, etc), align the stack correctly
   before calling the target function of the context.
   
   For i686 platform, The Linux ABI requires that the stack is aligned on a
   16-byte boundary at the time that a call is made, and the compiler
   attempts to maintain that alignment by adjusting the stack as required
   to meet the alignment requirements for data, and any subsequent calls.
   
   This is particularly important when compiling for i386 platform with
   -msse2, The compiler can emit code to use SSE2 instructions like
   `movaps`, which will actually fault on unalgned access. This causes the
   mariadb test suite to fail with the following error, for example:
   
   ```
   main.non_blocking_api                    w4 [ fail ]
           Test ended at 2023-08-18 00:33:40
   
   CURRENT_TEST: main.non_blocking_api
   mysqltest got signal 11
   read_command_buf (0x89a2a88): connect (con_nonblock,localhost,root,,test)
   
   conn->name (0x89c7208):
   
   Attempting backtrace...
   stack_bottom = 0x0 thread_stack 0x10000
   mysys/stacktrace.c:213(my_print_stacktrace)[0x80a7348]
   bits/stdio2.h:97(fprintf)[0x80615f2]
   addr2line: '': No such file
   [0xf7ee8560]
   ??:0(BIO_f_buffer)[0xf7bc1ca1]
   ??:0(BIO_vsnprintf)[0xf7bc2aa1]
   ??:0(BIO_snprintf)[0xf7bc2af4]
   ??:0(ASN1_UTCTIME_adj)[0xf7be0875]
   ??:0(X509_time_adj_ex)[0xf7c062dd]
   ??:0(X509_time_adj)[0xf7c06312]
   ??:0(X509_cmp_time)[0xf7c06516]
   ??:0(X509_cmp_time)[0xf7c06720]
   ??:0(X509_verify_cert)[0xf7c08641]
   ??:0(ssl_verify_cert_chain)[0xf7d172e1]
   ??:0(ssl3_get_server_certificate)[0xf7cefc96]
   ??:0(ssl3_connect)[0xf7cf520b]
   ??:0(ssl23_connect)[0xf7cfee42]
   secure/openssl.c:487(ma_tls_connect)[0x808ac22]
   libmariadb/ma_tls.c:83(ma_pvio_tls_connect)[0x807d82d]
   libmariadb/ma_pvio.c:531(ma_pvio_start_ssl)[0x807d553]
   auth/my_auth.c:318(send_client_reply_packet)[0x808f5db]
   auth/my_auth.c:94(native_password_auth_client)[0x808f84e]
   auth/my_auth.c:620(run_plugin_auth)[0x808fb5c]
   libmariadb/mariadb_lib.c:1665(mthd_my_real_connect)[0x807a121]
   libmariadb/mariadb_async.c:332(mysql_real_connect_start_internal)[0x808b3d9]
   libmariadb/ma_context.c:440(my_context_spawn)[0x808ed69]
   libmariadb/mariadb_lib.c:3927(mariadb_get_socket)[0x8078c6f]
   tests/nonblock-wrappers.h:96(wait_for_mysql(st_mysql*, int))[0x806117e]
   ```
   
   In this case, the eventual crash is in openssl code, but this is a
   conseqeunce of a `movaps` instruction in `BIO_f_buffer` acting on an
   unaligned stack location, which is in turn a result of the unaligned
   stack from `my_context_spawn`. Any use of SSE2 instructions requiring
   alignment will fail in the same way

   

   peadar committed Aug 18, 2023
   Configuration menu

   • View commit details
   • Copy full SHA for 2f5df4c
   • Browse repository at this point

   Copy the full SHA

   2f5df4c View commit details

   Browse the repository at this point in the history