Detect if atomic 64-bit load from RO memory works

diff --git a/debian/patches/0010-Detect-if-atomic-64-bit-load-from-RO-memory-works.patch b/debian/patches/0010-Detect-if-atomic-64-bit-load-from-RO-memory-works.patch
new file mode 100644 (file)
index 0000000..9f1d8f2
--- /dev/null
+++ b/debian/patches/0010-Detect-if-atomic-64-bit-load-from-RO-memory-works.patch
@@ -0,0 +1,97 @@
+From: =?utf-8?q?St=C3=A9phane_Glondu?= <glondu@debian.org>
+Date: Fri, 28 Jun 2024 07:53:21 +0200
+Subject: Detect if atomic 64-bit load from RO memory works
+
+Bug: https://github.com/ocaml/ocaml/issues/13234
+Forwarded: https://github.com/ocaml/ocaml/pull/13267
+---
+ aclocal.m4                                         | 21 +++++++++++++++++++++
+ configure.ac                                       |  5 +++++
+ otherlibs/runtime_events/runtime_events_consumer.c | 11 +++++++++--
+ runtime/caml/s.h.in                                |  2 ++
+ 4 files changed, 37 insertions(+), 2 deletions(-)
+
+diff --git a/aclocal.m4 b/aclocal.m4
+index cb73385..6f8e119 100644
+--- a/aclocal.m4
++++ b/aclocal.m4
+@@ -573,3 +573,24 @@ AC_DEFUN([OCAML_CC_SUPPORTS_ATOMIC], [
+    AC_MSG_RESULT([no])])
+   LIBS="$saved_LIBS"
+ ])
++
++AC_DEFUN([OCAML_ATOMIC_LOAD64_RW_CHECK], [
++  AC_MSG_CHECKING([whether atomic 64-bit load from RO memory works])
++  saved_LIBS="$LIBS"
++  LIBS="$LIBS $1"
++  OCAML_RUN_IFELSE([AC_LANG_SOURCE([[
++    #include <stdlib.h>
++    #include <stdint.h>
++    #include <stdatomic.h>
++    #include <sys/mman.h>
++    int main() {
++      uint64_t *a = mmap(NULL, 64, PROT_READ, MAP_ANONYMOUS | MAP_SHARED, 0, 0);
++      uint64_t b = atomic_load_explicit(a, memory_order_acquire);
++      return 0;
++    }
++    ]])],
++  [AC_MSG_RESULT([yes])],
++  [AC_DEFINE([ATOMIC_LOAD64_RW]) AC_MSG_RESULT([no])],
++  [AC_MSG_RESULT([cross-compiling; assume yes])])
++  LIBS="$saved_LIBS"
++])
+diff --git a/configure.ac b/configure.ac
+index a8e4222..6cd9b64 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -1162,6 +1162,11 @@ OCAML_CC_SUPPORTS_ATOMIC([$cclibs])
+ AS_IF([! $cc_supports_atomic],
+   [AC_MSG_FAILURE([C11 atomic support is required, use another C compiler])])
+ 
++# Atomic 64-bit load requires RW memory on at least Debian armel
++# See: https://github.com/ocaml/ocaml/issues/13234
++
++OCAML_ATOMIC_LOAD64_RW_CHECK([$cclibs])
++
+ # Full support for thread local storage
+ # macOS and MinGW-w64 have problems with thread local storage accessed from DLLs
+ 
+diff --git a/otherlibs/runtime_events/runtime_events_consumer.c b/otherlibs/runtime_events/runtime_events_consumer.c
+index 9df4eb5..c3c7aca 100644
+--- a/otherlibs/runtime_events/runtime_events_consumer.c
++++ b/otherlibs/runtime_events/runtime_events_consumer.c
+@@ -189,7 +189,14 @@ caml_runtime_events_create_cursor(const char_os* runtime_events_path, int pid,
+ 
+   cursor->ring_file_size_bytes = GetFileSize(cursor->ring_file_handle, NULL);
+ #else
+-  ring_fd = open(runtime_events_loc, O_RDONLY, 0);
++#ifndef ATOMIC_LOAD64_RW
++  const int open_flags = O_RDONLY;
++  const int mmap_prot = PROT_READ;
++#else
++  const int open_flags = O_RDWR;
++  const int mmap_prot = PROT_READ | PROT_WRITE;
++#endif
++  ring_fd = open(runtime_events_loc, open_flags, 0);
+ 
+   if( ring_fd == -1 ) {
+     caml_stat_free(cursor);
+@@ -210,7 +217,7 @@ caml_runtime_events_create_cursor(const char_os* runtime_events_path, int pid,
+   /* This cast is necessary for compatibility with Illumos' non-POSIX
+     mmap/munmap */
+   cursor->metadata = (struct runtime_events_metadata_header *)
+-                      mmap(NULL, cursor->ring_file_size_bytes, PROT_READ,
++                      mmap(NULL, cursor->ring_file_size_bytes, mmap_prot,
+                           MAP_SHARED, ring_fd, 0);
+ 
+   if( cursor->metadata == MAP_FAILED ) {
+diff --git a/runtime/caml/s.h.in b/runtime/caml/s.h.in
+index 0dc2ed7..bf9cca0 100644
+--- a/runtime/caml/s.h.in
++++ b/runtime/caml/s.h.in
+@@ -309,3 +309,5 @@
+ #undef HAS_BSD_GETAFFINITY_NP
+ 
+ #undef HAS_ZSTD
++
++#undef ATOMIC_LOAD64_RW

diff --git a/debian/patches/series b/debian/patches/series
index 65399d578f83bef64528bd55c5dd696a66fbc555..f7cb23dfc580fe0d3757c4e85277f4e80ac1bc30 100644 (file)
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -7,3 +7,4 @@
 0008-Filter-out-f-debug-file-prefix-map-from-ocamlc_cflag.patch
 0008-Fix-call-to-test-in-configure.ac.patch
 0009-Remove-fixed-register-assignments-on-m68k.patch
+0010-Detect-if-atomic-64-bit-load-from-RO-memory-works.patch