This adds SIGSEGV_FAULT_STACKPOINTER for the hurd-amd64 case
--- ./lib/sigsegv.c.original 2023-05-05 10:45:54.673751100 +0000
+++ ./lib/sigsegv.c 2023-05-05 10:48:47.903577554 +0000
@@ -351,6 +351,17 @@
"old esp, if trapped from user". */
# define SIGSEGV_FAULT_STACKPOINTER scp->sc_uesp
+# elif defined __x86_64__
+
+/* scp points to a 'struct sigcontext' (defined in
+ glibc/sysdeps/mach/hurd/x86_64/bits/sigcontext.h).
+ The registers of this struct get pushed on the stack through
+ gnumach/x86_64/i386/locore.S:trapall. */
+/* Both sc_rsp and sc_ursp appear to have the same value.
+ It appears more reliable to use sc_ursp because it is labelled as
+ "old rsp, if trapped from user". */
+# define SIGSEGV_FAULT_STACKPOINTER scp->sc_ursp
+
# endif
#endif
