[xen stable-4.21] tools/ocaml: Fix crash in Xenctrl.domain_getinfo{,list}() on ARM

[patchbot@xxxxxxx]

commit fbfca3287498cbb28b762607ac69022221e32381
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jul 28 10:52:49 2026 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Jul 29 13:42:15 2026 +0100

    tools/ocaml: Fix crash in Xenctrl.domain_getinfo{,list}() on ARM
    
    The Store_field(result, 16, arch_config) sits inside an #ifdef x86, meaning
    that on other architectures the pointer is not filled in.  Ocaml code then
    falls over a NULL(ish) pointer (really the Val_unit used to initialise
    'result') when the layout in the heap doesn't match the type system.
    
    Rearrange alloc_domaininfo() to avoid this.  Similarly to
    physinfo_arch_caps(), raise an exception if the architecture code hasn't
    filled in an appropriate tag.  Move the setup of arch_domainconfig to be
    common logic.
    
    In order to simplify the addition of other architectures, remove the
    arch_config variable (reusing tmp as it's touched exactly once), and rename
    x86_arch_config to be arch_config so each architecture can fill in a 
suitable
    one without needing more local variables.
    
    Fixes: 9d683b5e375d ("tools/ocaml: Expose arch_config in domaininfo")
    Fixes: 81838c9067ab ("ocaml: fix arm build")
    Reported-by: Julian Vetter <julian.vetter@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    (cherry picked from commit 365d2a5be3fa34b22c37ef4b6ff3efd3ce05b387)
---
 tools/ocaml/libs/xc/xenctrl_stubs.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c 
b/tools/ocaml/libs/xc/xenctrl_stubs.c
index c55f73b265..1dd01c0f69 100644
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -414,7 +414,8 @@ CAMLprim value stub_xc_domain_shutdown(value xch_val, value 
domid, value reason)
 static value alloc_domaininfo(xc_domaininfo_t * info)
 {
        CAMLparam0();
-       CAMLlocal5(result, tmp, arch_config, x86_arch_config, emul_list);
+       CAMLlocal4(result, tmp, arch_config, emul_list);
+       int tag = -1;
        int i;
 
        result = caml_alloc_tuple(17);
@@ -444,6 +445,9 @@ static value alloc_domaininfo(xc_domaininfo_t * info)
        Store_field(result, 15, tmp);
 
 #if defined(__i386__) || defined(__x86_64__)
+
+       tag = 1; /* tag x86 */
+
        /*
         * emulation_flags: x86_arch_emulation_flags list;
         */
@@ -452,16 +456,17 @@ static value alloc_domaininfo(xc_domaininfo_t * info)
                (info->arch_config.emulation_flags);
 
        /* xen_x86_arch_domainconfig */
-       x86_arch_config = caml_alloc_tuple(1);
-       Store_field(x86_arch_config, 0, emul_list);
+       arch_config = caml_alloc_tuple(1);
+       Field(arch_config, 0) = emul_list;
 
-       /* arch_config: arch_domainconfig */
-       arch_config = caml_alloc_small(1, 1);
-
-       Store_field(arch_config, 0, x86_arch_config);
-
-       Store_field(result, 16, arch_config);
 #endif
+       if (tag < 0)
+               caml_failwith("Unimplemented architecture in 
alloc_domaininfo()");
+
+       /* arch_config: arch_domainconfig */
+       tmp = caml_alloc_small(1, tag);
+       Field(tmp, 0) = arch_config;
+       Field(result, 16) = tmp;
 
        CAMLreturn(result);
 }
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.21