https://phabricator.services.mozilla.com/D142407

--- a/pr/include/md/_linux.h
+++ b/pr/include/md/_linux.h
@@ -71,10 +71,12 @@
 #define _PR_SI_ARCHITECTURE "microblaze"
 #elif defined(__nds32__)
 #define _PR_SI_ARCHITECTURE "nds32"
 #elif defined(__xtensa__)
 #define _PR_SI_ARCHITECTURE "xtensa"
+#elif defined(__loongarch64)
+#define _PR_SI_ARCHITECTURE "loongarch64"
 #else
 #error "Unknown CPU architecture"
 #endif
 #define PR_DLL_SUFFIX       ".so"
 
@@ -139,10 +141,22 @@
 #define _MD_ATOMIC_ADD                _PR_x86_64_AtomicAdd
 extern PRInt32 _PR_x86_64_AtomicSet(PRInt32 *val, PRInt32 newval);
 #define _MD_ATOMIC_SET                _PR_x86_64_AtomicSet
 #endif
 
+#if defined(__loongarch__)
+#if defined(__GNUC__)
+/* Use GCC built-in functions */
+#define _PR_HAVE_ATOMIC_OPS
+#define _MD_INIT_ATOMIC()
+#define _MD_ATOMIC_INCREMENT(ptr) __sync_add_and_fetch(ptr, 1)
+#define _MD_ATOMIC_DECREMENT(ptr) __sync_sub_and_fetch(ptr, 1)
+#define _MD_ATOMIC_ADD(ptr, i) __sync_add_and_fetch(ptr, i)
+#define _MD_ATOMIC_SET(ptr, nv) __sync_lock_test_and_set(ptr, nv)
+#endif
+#endif
+
 #if defined(__or1k__)
 #if defined(__GNUC__)
 /* Use GCC built-in functions */
 #define _PR_HAVE_ATOMIC_OPS
 #define _MD_INIT_ATOMIC()
--- a/pr/include/md/_linux.cfg
+++ b/pr/include/md/_linux.cfg
@@ -1253,10 +1253,56 @@
 #define PR_ALIGN_OF_WORD    8
 
 #define PR_BYTES_PER_WORD_LOG2  3
 #define PR_BYTES_PER_DWORD_LOG2 3
 
+#elif defined(__loongarch64)
+
+#undef  IS_BIG_ENDIAN
+#define IS_LITTLE_ENDIAN 1
+#define IS_64
+
+#define PR_BYTES_PER_BYTE   1
+#define PR_BYTES_PER_SHORT  2
+#define PR_BYTES_PER_INT    4
+#define PR_BYTES_PER_INT64  8
+#define PR_BYTES_PER_LONG   8
+#define PR_BYTES_PER_FLOAT  4
+#define PR_BYTES_PER_DOUBLE 8
+#define PR_BYTES_PER_WORD   8
+#define PR_BYTES_PER_DWORD  8
+
+#define PR_BITS_PER_BYTE    8
+#define PR_BITS_PER_SHORT   16
+#define PR_BITS_PER_INT     32
+#define PR_BITS_PER_INT64   64
+#define PR_BITS_PER_LONG    64
+#define PR_BITS_PER_FLOAT   32
+#define PR_BITS_PER_DOUBLE  64
+#define PR_BITS_PER_WORD    64
+
+#define PR_BITS_PER_BYTE_LOG2   3
+#define PR_BITS_PER_SHORT_LOG2  4
+#define PR_BITS_PER_INT_LOG2    5
+#define PR_BITS_PER_INT64_LOG2  6
+#define PR_BITS_PER_LONG_LOG2   6
+#define PR_BITS_PER_FLOAT_LOG2  5
+#define PR_BITS_PER_DOUBLE_LOG2 6
+#define PR_BITS_PER_WORD_LOG2   6
+
+#define PR_ALIGN_OF_SHORT   2
+#define PR_ALIGN_OF_INT     4
+#define PR_ALIGN_OF_LONG    8
+#define PR_ALIGN_OF_INT64   8
+#define PR_ALIGN_OF_FLOAT   4
+#define PR_ALIGN_OF_DOUBLE  8
+#define PR_ALIGN_OF_POINTER 8
+#define PR_ALIGN_OF_WORD    8
+
+#define PR_BYTES_PER_WORD_LOG2  3
+#define PR_BYTES_PER_DWORD_LOG2 3
+
 #else
 
 #error "Unknown CPU architecture"
 
 #endif