tools/ocaml: Introduce xenctrl ABI build-time checks

c/s f089fddd94 broke the Ocaml ABI by renumering
XEN_SYSCTL_PHYSCAP_directio without adjusting the Ocaml
physinfo_cap_flag enumeration.

Add build machinery which will check the ABI correspondence.

This will result in a compile time failure whenever constants get
renumbered/added without a compatible adjustment to the Ocaml ABI.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <Andrew.Cooper3@citrix.com>

.gitignore

@@ -392,6 +392,7 @@ tools/ocaml/libs/xentoollog/_xtl_levels.*
 tools/ocaml/libs/xentoollog/xentoollog.ml
 tools/ocaml/libs/xentoollog/xentoollog.mli
 tools/ocaml/libs/xs/paths.ml
+tools/ocaml/libs/xc/xenctrl_abi_check.h
 tools/ocaml/xenstored/_paths.h
 tools/ocaml/xenstored/oxenstored
 tools/ocaml/xenstored/oxenstored.conf

tools/ocaml/libs/xc/Makefile

@@ -31,4 +31,11 @@ install: $(LIBS) META
 uninstall:
 	$(OCAMLFIND) remove -destdir $(OCAMLDESTDIR) xenctrl
 
+xenctrl_stubs.o: xenctrl_abi_check.h
+
+xenctrl_abi_check.h: abi-check xenctrl_stubs.c xenctrl.ml
+	$(PERL) -w $^ >$@.tmp && mv -f $@.tmp $@
+
+GENERATED_FILES += xenctrl_abi_check.h
+
 include $(TOPLEVEL)/Makefile.rules

tools/ocaml/libs/xc/abi-check

@@ -0,0 +1,84 @@
+#!/usr/bin/perl -w
+
+use strict;
+use Data::Dumper;
+
+our %enums;
+
+@ARGV == 2 or die;
+our ($c, $o) = @ARGV;
+
+open STDIN, "<", $c or die $!;
+
+our $cline = -1;
+our $ei;
+
+while (<>) {
+    if ($cline == -1) {
+        if (m/c_bitmap_to_ocaml_list/) {
+            $cline = 0;
+            $ei = { };
+        }
+    } else {
+        $cline++;
+        m{^\s+/\* \s+ ! \s+ (.*?) \s* \*/\s*$}x or die "$cline $_ ?";
+        my @vals = split /\s+/, $1;
+        if ($cline == 1 && !@vals) {
+            $cline = -1;
+        } elsif ($cline == 1 && @vals == 3) {
+            $ei->{$_} = shift @vals foreach qw(OType OPrefix Mangle);
+        } elsif ($cline == 2 && @vals == 3) {
+            $ei->{$_} = shift @vals foreach qw(CPrefix CFinal CFinalHow);
+            die if $enums{ $ei->{OType} };
+            $enums{ $ei->{OType} } = $ei;
+            $cline = -1;
+        } else {
+            die "$_ ?";
+        }
+    }
+}
+
+sub expect ($$) {
+    printf "BUILD_BUG_ON( %-30s != %-10s );\n", @_ or die $!;
+}
+
+open STDIN, "<", $o or die $!;
+my $cval;
+$ei = undef;
+my $bitnum = 0;
+while (<>) {
+    if (!$ei) {
+        if (m{^type \s+ (\w+) \s* \= \s* $/}x && $enums{$1}) {
+            $ei = $enums{$1};
+            $cval = '';
+            $bitnum = 0;
+        }
+    } else {
+        if (m{^\s+ \| \s* $ei->{OPrefix} (\w+) \s*$}x) {
+            $cval = $1;
+            if ($ei->{Mangle} eq 'lc') {
+                $cval = lc $cval;
+            } elsif ($ei->{Mangle} eq 'none') {
+            } else {
+                die;
+            }
+            $cval = $ei->{CPrefix}.$cval;
+            expect($cval, "(1u << $bitnum)");
+            $bitnum++;
+        } elsif (m/^\w|\{/) {
+            if ($ei->{CFinalHow} eq 'max') {
+                expect($ei->{CFinal}, "(1u << ".($bitnum-1).")");
+            } elsif ($ei->{CFinalHow} eq 'all') {
+                expect($ei->{CFinal}, "(1u << $bitnum)-1u");
+            } else {
+                die Dumper($ei)." ?";
+            }
+            $ei = undef;
+        } elsif (!m{\S}) {
+        } else {
+            die "$_ ?";
+        }
+    }
+}
+
+close STDOUT or die $!;

tools/ocaml/libs/xc/xenctrl_stubs.c

@@ -32,6 +32,7 @@
 
 #define XC_WANT_COMPAT_MAP_FOREIGN_API
 #include <xenctrl.h>
+#include <xen-tools/libs.h>
 
 #include "mmap_stubs.h"
 
@@ -119,6 +120,39 @@ static void domain_handle_of_uuid_string(xen_domain_handle_t h,
 #undef X
 }
 
+/*
+ * Various fields which are a bitmap in the C ABI are converted to lists of
+ * integers in the Ocaml ABI for more idiomatic handling.
+ */
+static value c_bitmap_to_ocaml_list
+             /* ! */
+             /*
+	      * All calls to this function must be in a form suitable
+	      * for xenctrl_abi_check.  The parsing there is ad-hoc.
+	      */
+             (unsigned int bitmap)
+{
+	CAMLparam0();
+	CAMLlocal2(list, tmp);
+
+#include "xenctrl_abi_check.h"
+
+	list = tmp = Val_emptylist;
+
+	for ( unsigned int i = 0; bitmap; i++, bitmap >>= 1 )
+	{
+		if ( !(bitmap & 1) )
+			continue;
+
+		tmp = caml_alloc_small(2, Tag_cons);
+		Field(tmp, 0) = Val_int(i);
+		Field(tmp, 1) = list;
+		list = tmp;
+	}
+
+	CAMLreturn(list);
+}
+
 CAMLprim value stub_xc_domain_create(value xch, value config)
 {
 	CAMLparam2(xch, config);
@@ -315,16 +349,13 @@ static value alloc_domaininfo(xc_domaininfo_t * info)
 	Store_field(result, 15, tmp);
 
 #if defined(__i386__) || defined(__x86_64__)
-	/* emulation_flags: x86_arch_emulation_flags list; */
-	tmp = emul_list = Val_emptylist;
-	for (i = 0; i < 10; i++) {
-		if ((info->arch_config.emulation_flags >> i) & 1) {
-			tmp = caml_alloc_small(2, Tag_cons);
-			Field(tmp, 0) = Val_int(i);
-			Field(tmp, 1) = emul_list;
-			emul_list = tmp;
-		}
-	}
+	/*
+	 * emulation_flags: x86_arch_emulation_flags list;
+	 */
+	emul_list = c_bitmap_to_ocaml_list
+		/* ! x86_arch_emulation_flags X86_EMU_ none */
+		/* ! XEN_X86_EMU_ XEN_X86_EMU_ALL all */
+		(info->arch_config.emulation_flags);
 
 	/* xen_x86_arch_domainconfig */
 	x86_arch_config = caml_alloc_tuple(1);
@@ -635,7 +666,7 @@ CAMLprim value stub_xc_send_debug_keys(value xch, value keys)
 CAMLprim value stub_xc_physinfo(value xch)
 {
 	CAMLparam1(xch);
-	CAMLlocal3(physinfo, cap_list, tmp);
+	CAMLlocal2(physinfo, cap_list);
 	xc_physinfo_t c_physinfo;
 	int r;
 
@@ -646,15 +677,13 @@ CAMLprim value stub_xc_physinfo(value xch)
 	if (r)
 		failwith_xc(_H(xch));
 
-	tmp = cap_list = Val_emptylist;
-	for (r = 0; r < 2; r++) {
-		if ((c_physinfo.capabilities >> r) & 1) {
-			tmp = caml_alloc_small(2, Tag_cons);
-			Field(tmp, 0) = Val_int(r);
-			Field(tmp, 1) = cap_list;
-			cap_list = tmp;
-		}
-	}
+	/*
+	 * capabilities: physinfo_cap_flag list;
+	 */
+	cap_list = c_bitmap_to_ocaml_list
+		/* ! physinfo_cap_flag CAP_ lc */
+		/* ! XEN_SYSCTL_PHYSCAP_ XEN_SYSCTL_PHYSCAP_MAX max */
+		(c_physinfo.capabilities);
 
 	physinfo = caml_alloc_tuple(10);
 	Store_field(physinfo, 0, Val_int(c_physinfo.threads_per_core));

xen/include/public/sysctl.h

@@ -90,6 +90,10 @@ struct xen_sysctl_tbuf_op {
  /* The platform supports direct access to I/O devices with IOMMU. */
 #define _XEN_SYSCTL_PHYSCAP_directio     2
 #define XEN_SYSCTL_PHYSCAP_directio  (1u<<_XEN_SYSCTL_PHYSCAP_directio)
+
+/* Max XEN_SYSCTL_PHYSCAP_* constant.  Used for ABI checking. */
+#define XEN_SYSCTL_PHYSCAP_MAX XEN_SYSCTL_PHYSCAP_directio
+
 struct xen_sysctl_physinfo {
     uint32_t threads_per_core;
     uint32_t cores_per_socket;