diff --git a/src/flamenco/vm/fd_vm_cpi.h b/src/flamenco/vm/fd_vm_cpi.h
index b3c1627a3d..858a4c802e 100644
--- a/src/flamenco/vm/fd_vm_cpi.h
+++ b/src/flamenco/vm/fd_vm_cpi.h
@@ -3,6 +3,23 @@
 
 #include "../fd_flamenco_base.h"
 
+/* fd_vm_cpi contains type definitions for the cross-program-invocation
+   (CPI) API.  These types are passed from the virtual machine to the
+   CPI syscall handlers and are thus untrusted.  Addresses are in VM
+   address space.  Struct parameter offsets and sizes match exactly.
+   Structs also have alignment requirements in VM address space.  These
+   alignments are provided as const macros.  Since we cannot guarantee
+   that a type is aligned in host address space even when aligned in
+   VM address space, all structs support unaligned access
+   (i.e. alignof(type)==1UL).
+
+   Unfortunately, the Solana protocol provides this API twice:
+   In a C-style ABI and in Rust ABI. */
+
+/* fd_vm_vec_t is the in-memory representation of a vector descriptor.
+   Equal in layout to the Rust slice header &[_] and various vector
+   types in the C version of the syscall API. */
+
 #define FD_VM_VEC_ALIGN (8UL)
 
 struct __attribute__((packed)) fd_vm_vec {
@@ -12,4 +29,134 @@ struct __attribute__((packed)) fd_vm_vec {
 
 typedef struct fd_vm_vec fd_vm_vec_t;
 
+#define FD_VM_RC_REFCELL_ALIGN (8UL)
+
+struct __attribute__((packed)) fd_vm_rc_refcell_vec {
+  ulong strong;
+  ulong weak;
+  ulong borrow;
+  ulong addr;
+  ulong len;
+};
+typedef struct fd_vm_rc_refcell_vec fd_vm_rc_refcell_vec_t;
+
+struct __attribute__((packed)) fd_vm_rc_refcell {
+  ulong strong;
+  ulong weak;
+  ulong borrow;
+  ulong addr;
+};
+typedef struct fd_vm_rc_refcell fd_vm_rc_refcell_t;
+
+/* Structs fd_vm_c_{...}_t are part of the C ABI for the cross-program
+   invocation syscall API. */
+
+#define FD_VM_C_INSTRUCTION_ALIGN (8UL)
+
+struct __attribute__((packed)) fd_vm_c_instruction {
+  ulong  program_id_addr;
+  ulong  accounts_addr;
+  ulong  accounts_len;
+  ulong  data_addr;
+  ulong  data_len;
+};
+
+typedef struct fd_vm_c_instruction fd_vm_c_instruction_t;
+
+#define FD_VM_C_ACCOUNT_META_ALIGN (8UL)
+
+struct fd_vm_c_account_meta {
+  ulong pubkey_addr;
+  uchar is_writable;
+  uchar is_signer;
+};
+
+typedef struct fd_vm_c_account_meta fd_vm_c_account_meta_t;
+
+#define FD_VM_C_ACCOUNT_INFO_ALIGN (8UL)
+
+struct fd_vm_c_account_info {
+  ulong key_addr;
+  ulong lamports_addr;
+  ulong data_sz;
+  ulong data_addr;
+  ulong owner_addr;
+  ulong rent_epoch;
+  uchar is_signer;
+  uchar is_writable;
+  uchar executable;
+};
+
+typedef struct fd_vm_c_account_info fd_vm_c_account_info_t;
+
+/* Structs fd_vm_rust_{...}_t are part of the Rust ABI for the
+   cross-program-invocation syscall API. */
+
+/* fd_vm_rust_vec_t is Rust type Vec<_> using the default allocator. */
+
+#define FD_VM_RUST_VEC_ALIGN (8UL)
+
+struct __attribute__((packed)) fd_vm_rust_vec {
+  ulong addr;
+  ulong cap;
+  ulong len;
+};
+
+typedef struct fd_vm_rust_vec fd_vm_rust_vec_t;
+
+#define FD_VM_RUST_RC_ALIGN (8UL)
+
+#define FD_VM_RUST_INSTRUCTION_ALIGN (8UL)
+
+struct __attribute__((packed)) fd_vm_rust_instruction {
+  fd_vm_rust_vec_t accounts;    /* points to fd_vm_rust_account_meta_t */
+  fd_vm_rust_vec_t data;        /* points to bytes */
+  uchar            pubkey[32];
+};
+
+typedef struct fd_vm_rust_instruction fd_vm_rust_instruction_t;
+
+#define FD_VM_RUST_ACCOUNT_META_ALIGN (1UL)
+
+struct __attribute__((packed)) fd_vm_rust_account_meta {
+  uchar pubkey[32];
+  uchar is_signer;
+  uchar is_writable;
+};
+
+typedef struct fd_vm_rust_account_meta fd_vm_rust_account_meta_t;
+
+#define FD_VM_RUST_ACCOUNT_INFO_ALIGN (8UL)
+
+struct __attribute__((packed)) fd_vm_rust_account_info {
+  ulong pubkey_addr;          /* points to uchar[32] */
+  ulong lamports_box_addr;    /* points to Rc with embedded RefCell which points to u64 */
+  ulong data_box_addr;        /* points to Rc with embedded RefCell which contains slice which points to bytes */
+  ulong owner_addr;           /* points to uchar[32] */
+  ulong rent_epoch;
+  uchar is_signer;
+  uchar is_writable;
+  uchar executable;
+  uchar _padding_0[5];
+};
+
+typedef struct fd_vm_rust_account_info fd_vm_rust_account_info_t;
+
+union fd_vm_account_info_inner {
+  fd_vm_rust_account_info_t const * rust_acct_infos;
+  fd_vm_c_account_info_t    const *    c_acct_infos;
+};
+
+typedef union fd_vm_account_info_inner fd_vm_account_info_inner_t;
+
+struct __attribute__((packed)) fd_vm_account_info {
+  uint discriminant;
+# define FD_VM_ACCOUNT_INFO_RUST (0U)
+# define FD_VM_ACCOUNT_INFO_C    (1U)
+
+  fd_vm_account_info_inner_t inner;
+};
+
+typedef struct fd_vm_account_info fd_vm_account_info_t;
+
 #endif /* HEADER_fd_src_flamenco_vm_fd_vm_cpi_h */