diff --git a/risu.h b/risu.h
index 4203178..0ac7d1e 100644
--- a/risu.h
+++ b/risu.h
@@ -68,7 +68,7 @@ typedef enum {
 
 /* This is the data structure we pass over the socket for OP_COMPARE
  * and OP_TESTEND. It is a simplified and reduced subset of what can
- * be obtained with a ucontext_t*, and is architecture specific
+ * be obtained with a ucontext_t, and is architecture specific
  * (defined in risu_reginfo_*.h).
  */
 struct reginfo;
@@ -93,14 +93,14 @@ void send_response_byte(int sock, int resp);
 
 /* Interface provided by CPU-specific code: */
 
-/* Move the PC past this faulting insn by adjusting ucontext. */
-void advance_pc(void *uc);
+/* Move the PC past this faulting insn by adjusting signal context. */
+void advance_pc(host_context_t *hc);
 
-/* Set the parameter register in a ucontext_t to the specified value.
+/*
+ * Set the parameter register in a host_context_t to the specified value.
  * (32-bit targets can ignore high 32 bits.)
- * vuc is a ucontext_t* cast to void*.
  */
-void set_ucontext_paramreg(void *vuc, uint64_t value);
+void set_ucontext_paramreg(host_context_t *hc, uint64_t value);
 
 /* Return the value of the parameter register from a reginfo. */
 uint64_t get_reginfo_paramreg(struct reginfo *ri);
@@ -114,8 +114,8 @@ RisuOp get_risuop(struct reginfo *ri);
 /* Return the PC from a reginfo */
 uintptr_t get_pc(struct reginfo *ri);
 
-/* initialize structure from a ucontext */
-void reginfo_init(struct reginfo *ri, ucontext_t *uc, void *siaddr);
+/* initialize structure from a host_context_t. */
+void reginfo_init(struct reginfo *ri, host_context_t *hc, void *siaddr);
 
 /* return true if structs are equal, false otherwise. */
 bool reginfo_is_eq(struct reginfo *r1, struct reginfo *r2);
diff --git a/risu_reginfo_aarch64.h b/risu_reginfo_aarch64.h
index 097b7ad..bc3a661 100644
--- a/risu_reginfo_aarch64.h
+++ b/risu_reginfo_aarch64.h
@@ -15,6 +15,8 @@
 
 #include <signal.h>
 
+typedef ucontext_t host_context_t;
+
 /* The kernel headers set this based on future arch extensions.
    The current arch maximum is 16.  Save space below.  */
 #undef SVE_VQ_MAX
diff --git a/risu_reginfo_arm.h b/risu_reginfo_arm.h
index 60754a9..1937e46 100644
--- a/risu_reginfo_arm.h
+++ b/risu_reginfo_arm.h
@@ -13,6 +13,8 @@
 #ifndef RISU_REGINFO_ARM_H
 #define RISU_REGINFO_ARM_H
 
+typedef ucontext_t host_context_t;
+
 struct reginfo {
     uint64_t fpregs[32];
     uint32_t faulting_insn;
diff --git a/risu_reginfo_i386.h b/risu_reginfo_i386.h
index b468f79..abbfbe1 100644
--- a/risu_reginfo_i386.h
+++ b/risu_reginfo_i386.h
@@ -12,6 +12,8 @@
 #ifndef RISU_REGINFO_I386_H
 #define RISU_REGINFO_I386_H
 
+typedef ucontext_t host_context_t;
+
 struct avx512_reg {
     uint64_t q[8];
 };
diff --git a/risu_reginfo_loongarch64.h b/risu_reginfo_loongarch64.h
index 892b477..6c85951 100644
--- a/risu_reginfo_loongarch64.h
+++ b/risu_reginfo_loongarch64.h
@@ -12,6 +12,9 @@
 #ifndef RISU_REGINFO_LOONGARCH64_H
 #define RISU_REGINFO_LOONGARCH64_H
 
+/* From kernel <asm/ucontext.h> not libc <ucontext.h>. */
+typedef struct ucontext host_context_t;
+
 struct reginfo {
     uint64_t regs[32];
     uint64_t pc;
diff --git a/risu_reginfo_m68k.h b/risu_reginfo_m68k.h
index c1c9fe6..233f901 100644
--- a/risu_reginfo_m68k.h
+++ b/risu_reginfo_m68k.h
@@ -9,6 +9,8 @@
 #ifndef RISU_REGINFO_M68K_H
 #define RISU_REGINFO_M68K_H
 
+typedef ucontext_t host_context_t;
+
 struct reginfo {
     uint32_t faulting_insn;
     uint32_t pc;
diff --git a/risu_reginfo_ppc64.h b/risu_reginfo_ppc64.h
index 4b1d8bd..424fd02 100644
--- a/risu_reginfo_ppc64.h
+++ b/risu_reginfo_ppc64.h
@@ -14,6 +14,8 @@
 #ifndef RISU_REGINFO_PPC64LE_H
 #define RISU_REGINFO_PPC64LE_H
 
+typedef ucontext_t host_context_t;
+
 struct reginfo {
     uint32_t faulting_insn;
     uint32_t prev_insn;
diff --git a/risu_reginfo_s390x.h b/risu_reginfo_s390x.h
index c65fff7..5126fd5 100644
--- a/risu_reginfo_s390x.h
+++ b/risu_reginfo_s390x.h
@@ -12,6 +12,8 @@
 #ifndef RISU_REGINFO_S390X_H
 #define RISU_REGINFO_S390X_H
 
+typedef ucontext_t host_context_t;
+
 struct reginfo {
     uint64_t psw_mask;
     uint64_t pc_offset;
diff --git a/risu_aarch64.c b/risu_aarch64.c
index f8a8412..af94539 100644
--- a/risu_aarch64.c
+++ b/risu_aarch64.c
@@ -12,15 +12,13 @@
 
 #include "risu.h"
 
-void advance_pc(void *vuc)
+void advance_pc(ucontext_t *uc)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.pc += 4;
 }
 
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(ucontext_t *uc, uint64_t value)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.regs[0] = value;
 }
 
diff --git a/risu_arm.c b/risu_arm.c
index a20bf73..0e72fba 100644
--- a/risu_arm.c
+++ b/risu_arm.c
@@ -38,16 +38,13 @@ int insnsize(ucontext_t *uc)
     return 4;
 }
 
-void advance_pc(void *vuc)
+void advance_pc(ucontext_t *uc)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.arm_pc += insnsize(uc);
 }
 
-
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(ucontext_t *uc, uint64_t value)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.arm_r0 = value;
 }
 
diff --git a/risu_i386.c b/risu_i386.c
index 127e816..5d3b8aa 100644
--- a/risu_i386.c
+++ b/risu_i386.c
@@ -16,10 +16,8 @@
 #include "risu.h"
 #include "risu_reginfo_i386.h"
 
-void advance_pc(void *vuc)
+void advance_pc(ucontext_t *uc)
 {
-    ucontext_t *uc = (ucontext_t *) vuc;
-
     /*
      * We assume that this is UD1 as per get_risuop below.
      * This would need tweaking if we want to test expected undefs.
@@ -27,9 +25,8 @@ void advance_pc(void *vuc)
     uc->uc_mcontext.gregs[REG_E(IP)] += 3;
 }
 
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(ucontext_t *uc, uint64_t value)
 {
-    ucontext_t *uc = (ucontext_t *) vuc;
     uc->uc_mcontext.gregs[REG_E(AX)] = value;
 }
 
diff --git a/risu_loongarch64.c b/risu_loongarch64.c
index b6c59cf..921a031 100644
--- a/risu_loongarch64.c
+++ b/risu_loongarch64.c
@@ -15,15 +15,13 @@
 
 #include "risu.h"
 
-void advance_pc(void *vuc)
+void advance_pc(host_context_t *uc)
 {
-    struct ucontext *uc = vuc;
     uc->uc_mcontext.sc_pc += 4;
 }
 
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(host_context_t *uc, uint64_t value)
 {
-    struct ucontext *uc = vuc;
     uc->uc_mcontext.sc_regs[4] = value;
 }
 
diff --git a/risu_m68k.c b/risu_m68k.c
index acdd57a..bd6bece 100644
--- a/risu_m68k.c
+++ b/risu_m68k.c
@@ -8,15 +8,13 @@
 
 #include "risu.h"
 
-void advance_pc(void *vuc)
+void advance_pc(ucontext_t *uc)
 {
-    ucontext_t *uc = (ucontext_t *) vuc;
     uc->uc_mcontext.gregs[R_PC] += 4;
 }
 
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(ucontext_t *uc, uint64_t value)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.gregs[R_A0] = value;
 }
 
diff --git a/risu_ppc64.c b/risu_ppc64.c
index 62cf6aa..06cb8a8 100644
--- a/risu_ppc64.c
+++ b/risu_ppc64.c
@@ -14,15 +14,13 @@
 #include "risu.h"
 #include <sys/user.h>
 
-void advance_pc(void *vuc)
+void advance_pc(ucontext_t *uc)
 {
-    ucontext_t *uc = (ucontext_t *) vuc;
     uc->uc_mcontext.regs->nip += 4;
 }
 
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(ucontext_t *uc, uint64_t value)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.gp_regs[0] = value;
 }
 
diff --git a/risu_reginfo_loongarch64.c b/risu_reginfo_loongarch64.c
index 6150a40..0719e8b 100644
--- a/risu_reginfo_loongarch64.c
+++ b/risu_reginfo_loongarch64.c
@@ -97,10 +97,9 @@ static int parse_extcontext(struct sigcontext *sc, struct extctx_layout *extctx)
 }
 
 /* reginfo_init: initialize with a ucontext */
-void reginfo_init(struct reginfo *ri, ucontext_t *context, void *siaddr)
+void reginfo_init(struct reginfo *ri, host_context_t *uc, void *siaddr)
 {
     int i;
-    struct ucontext *uc = (struct ucontext *)context;
     struct extctx_layout extctx;
 
     memset(&extctx, 0, sizeof(struct extctx_layout));
diff --git a/risu_s390x.c b/risu_s390x.c
index cf9c72c..906766e 100644
--- a/risu_s390x.c
+++ b/risu_s390x.c
@@ -13,7 +13,7 @@
 
 #include "risu.h"
 
-void advance_pc(void *vuc)
+void advance_pc(ucontext_t *uc)
 {
     /*
      * Note: The PSW address already points to the next instruction
@@ -21,9 +21,8 @@ void advance_pc(void *vuc)
      */
 }
 
-void set_ucontext_paramreg(void *vuc, uint64_t value)
+void set_ucontext_paramreg(ucontext_t *uc, uint64_t value)
 {
-    ucontext_t *uc = vuc;
     uc->uc_mcontext.gregs[0] = value;
 }
 
