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Ivan Gotovchits
3d4d214f51
The Linux kernel's ptrace_regset() (kernel/ptrace.c) writes min(iov_len, actual_size) bytes and returns success for any non-zero buffer; it never rejects a PTRACE_GETREGSET request solely because the buffer is smaller than the full register set. gVisor's PtraceGetRegSet previously returned EFAULT when maxlen was less than ptraceRegistersSize on both x86 and arm64. This broke any tool that passes a smaller buffer, most notably libunwind which passes sizeof(gregset_t) = 184 bytes rather than sizeof(user_regs_struct) = 216 bytes for the PTRACE_GETREGSET call, causing unw_init_remote() to fail with UNW_EBADREG and making ptrace-based stack unwinding non-functional inside gVisor containers. Fix PtraceGetRegSet on x86 and arm64 to write min(maxlen, ptraceRegistersSize) bytes when maxlen is positive but smaller than the full register set, matching Linux kernel semantics. Add a syscall test that exercises the partial read path and verifies the bytes written match the corresponding bytes from a full register read. Signed-off-by: Ivan Gotovchits <[email protected]>