Resolving MySQL 8.0.21 Client Segmentation Fault Caused by Missing ncurses and Implicit Function Declarations

The author, a MySQL DBA, encountered a segmentation fault when launching the MySQL 8.0.21 client compiled from source on CentOS 8.4 (gcc 8.4.1). The initial build failed due to missing ncurses, producing undefined‑reference errors; after installing the library the build succeeded, but the client crashed after login.

During the first compilation, several implicit‑declaration warnings appeared in terminal.c (e.g., tgetent , tgetflag , tgetnum , tgetstr ), indicating that the term.h header was not included because the ncurses development package was absent.

To capture a core dump on CentOS 8 (which disables core files by default), the author set the core pattern: # echo "core-%t.%p" > /proc/sys/kernel/core_pattern The resulting core file was examined with gdb, revealing a crash in terminal_alloc within terminal.c at line 350, ultimately traced to a faulty call to tgetstr .

Further analysis showed that tgetstr returned a pointer that was truncated to 32 bits on the 64‑bit system because the function prototype was missing, causing the pointer to be treated as an int . A small test program (foo/bar) reproduced the same truncation when compiled with the implicit‑declaration warning.

The root cause is the missing term.h header, leading to HAVE_TERM_H being undefined in the build configuration. The fix consists of:

Installing the ncurses development package (e.g., sudo yum install -y ncurses-devel ).

Cleaning the CMake cache ( rm CMakeCache.txt; rm -rf CMakeFiles ).

Rerunning cmake and make to rebuild the client without warnings.

After these steps the client no longer crashes. An alternative workaround is to modify terminal.c by removing the stack buffer char buf[TC_BUFSIZE] and setting area = NULL , forcing tgetstr to allocate memory on the heap, which avoids the truncation issue.

The article also explains the difference between heap and stack address spaces on Linux, illustrating why a heap‑allocated pointer may not be truncated if its value fits within 32 bits.

Reference to MySQL bug #58497 is provided for further reading.