Changeset 51949d0 in mainline

Timestamp:

2025-04-17T19:11:34Z (36 hours ago)

Author:

GitHub <noreply@…>

Branches:

master

Children:

94abc30c, e9bc927

Parents:

eb2187c4

git-author:

Miroslav Cimerman <70661600+mcimerman@…> (2025-04-17 19:11:34)

git-committer:

GitHub <noreply@…> (2025-04-17 19:11:34)

Message:

lib/c/arch/arm32: add atomic_compare_exchange_1 (#248)

File:

• uspace/lib/c/arch/arm32/src/atomic.c (modified) (2 diffs)

uspace/lib/c/arch/arm32/src/atomic.c

@@ -106 +106 @@
 }
 
-bool __atomic_compare_exchange_4(volatile void *mem0, void *expected0,
-    unsigned desired, bool weak, int success, int failure)
-{
-        volatile unsigned *mem = mem0;
-        unsigned *expected = expected0;
+bool __atomic_compare_exchange_1(volatile void *mem0, void *expected0,
+    unsigned char desired, bool weak, int success, int failure)
+{
+        volatile unsigned char *mem = mem0;
+        unsigned char *expected = expected0;
 
         (void) success;
@@ -116 +116 @@
         (void) weak;
 
+        unsigned char ov = *expected;
+        unsigned ret;
+
+        /*
+         * The following instructions between labels 1 and 2 constitute a
+         * Restartable Atomic Sequence. Should the sequence be non-atomic,
+         * the kernel will restart it.
+         */
+        asm volatile (
+            "1:\n"
+            "   adr %[ret], 1b\n"
+            "   str %[ret], %[rp0]\n"
+            "   adr %[ret], 2f\n"
+            "   str %[ret], %[rp1]\n"
+
+            "   ldrb %[ret], %[addr]\n"
+            "   cmp %[ret], %[ov]\n"
+            "   streqb %[nv], %[addr]\n"
+            "2:\n"
+            : [ret] "=&r" (ret),
+              [rp0] "=m" (ras_page[0]),
+              [rp1] "=m" (ras_page[1]),
+              [addr] "+m" (*mem)
+            : [ov] "r" (ov),
+              [nv] "r" (desired)
+        );
+
+        ras_page[0] = 0;
+        ras_page[1] = 0xffffffff;
+
+        if (ret == ov)
+                return true;
+
+        *expected = ret;
+        return false;
+}
+
+bool __atomic_compare_exchange_4(volatile void *mem0, void *expected0,
+    unsigned desired, bool weak, int success, int failure)
+{
+        volatile unsigned *mem = mem0;
+        unsigned *expected = expected0;
+
+        (void) success;
+        (void) failure;
+        (void) weak;
+
         unsigned ov = *expected;
         unsigned ret;