This error

openjdk/src/jdk.hotspot.agent/linux/native/libsaproc/ps_core.c:798:7: error: ignoring return value of 'pread', declared with attribute warn_unused_result [-Werror=unused-result]
       pread(ph->core->exec_fd, interp_name, exec_php->p_filesz, exec_php->p_offset);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

was seen while trying to build OpenJDK on an Ubuntu 18.04 VM with compiler

* Toolchain: gcc (GNU Compiler Collection)
* C Compiler: Version 7.3.0 (at /usr/bin/gcc)
* C++ Compiler: Version 7.3.0 (at /usr/bin/g++)

This change fixes the problem:

+++ b/src/jdk.hotspot.agent/linux/native/libsaproc/ps_core.c
@@ -795,7 +795,9 @@
       if (exec_php->p_filesz > BUF_SIZE) {
         goto err;
       }
- pread(ph->core->exec_fd, interp_name, exec_php->p_filesz, exec_php->p_offset);
+ if (pread(ph->core->exec_fd, interp_name, exec_php->p_filesz, exec_php->p_offset) != exec_php->p_filesz) {
+ goto err;
+ }
       interp_name[exec_php->p_filesz] = '\0';
       print_debug("ELF interpreter %s\n", interp_name);
       // read interpreter segments as well