================ @@ -229,3 +229,54 @@ bytes. `zt0`'s value and whether it is active or not will be saved prior to expression evaluation and restored afterwards. + +## Guarded Control Stack Extension (GCS) + +GCS support includes the following new registers: + +* `gcs_features_enabled` +* `gcs_features_locked` +* `gcspr_el0` + +These map to the registers ptrace provides. The first two have had a `gcs_` +prefix added as their names are too generic without it. + +When the GCS is enabled the kernel allocates a memory region for it. This region +has a special attribute that LLDB will detect and presents like this: +``` + (lldb) memory region --all + <...> + [0x0000fffff7a00000-0x0000fffff7e00000) rw- + shadow stack: yes + [0x0000fffff7e00000-0x0000fffff7e10000) --- +``` + +`shadow stack` is a generic term used in the kernel for secure stack +extensions like GCS. + +### Expression Evaluation + +To execute an expression, LLDB must push the return address of the expression +wrapper (usually the entry point of the program) to the Guarded Control Stack. +It does this by decrementing `gcspr_el0` and writing to the location that +`gcspr_el0` then points to (instead of using the GCS push instructions). + +After an expression finishes, LLDB will restore the contents of all 3 registers, +apart from the enable bit of `gcs_features_enabled`. + +This is because there are limits on how often and from where you can set this ---------------- omjavaid wrote:
This line should be part of the previous paragraph. https://github.com/llvm/llvm-project/pull/117860 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
