casaroli commented on code in PR #19772:
URL: https://github.com/apache/nuttx/pull/19772#discussion_r3757989412
##########
arch/xtensa/src/esp32s3/esp32s3_addrenv.c:
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@@ -577,6 +579,153 @@ int up_addrenv_clone(const arch_addrenv_t *src,
arch_addrenv_t *dest)
return OK;
}
+/****************************************************************************
+ * Name: copy_region
+ *
+ * Description:
+ * Copy one region's pages from a parent environment into a child's. Both
+ * sides are reached through the kernel's scratch region, which is why it
+ * has two slots: source and destination are mapped at the same time so
+ * this is one memcpy rather than a bounce through kernel memory.
+ *
+ * sched_lock() is held across each page pair for the reason every scratch
+ * mapping is: those addresses are ordinary external memory to the
+ * permission control, so no unprivileged task may run while a page of
+ * somebody's memory is parked at one.
+ *
+ ****************************************************************************/
+
+static int copy_region(const uintptr_t *src, uintptr_t *dest, uint16_t count)
+{
+ uint16_t i;
+
+ for (i = 0; i < count; i++)
+ {
+ uintptr_t svaddr;
+ uintptr_t dvaddr;
+
+ sched_lock();
+
+ svaddr = esp32s3_pgmap(src[i]);
+ dvaddr = esp32s3_pgmap(dest[i]);
+
+ if (svaddr == 0 || dvaddr == 0)
+ {
+ if (svaddr != 0)
+ {
+ esp32s3_pgunmap(svaddr);
+ }
+
+ if (dvaddr != 0)
+ {
+ esp32s3_pgunmap(dvaddr);
+ }
+
+ sched_unlock();
+ berr("ERROR: no scratch mapping for page %u\n", i);
+ return -EFAULT;
+ }
+
+ memcpy((void *)dvaddr, (const void *)svaddr, MM_PGSIZE);
+
+ esp32s3_pgunmap(dvaddr);
+ esp32s3_pgunmap(svaddr);
+
+ sched_unlock();
+ }
+
+ return OK;
+}
+
+/****************************************************************************
+ * Name: up_addrenv_fork
+ *
+ * Description:
+ * Duplicate an address environment for fork(): allocate the child pages
+ * to match the parent's regions and copy the parent's contents into them.
+ *
+ * The copy is eager and complete. There is no copy-on-write and no demand
+ * fill, because this chip provides no synchronous restartable write fault
+ * to build them on -- proven, not assumed. So a fork costs a full copy of
+ * the process image.
+ *
+ * The child's pages land at the same *virtual* addresses as the parent's,
+ * which is the property the whole thing rests on: a copied stack is full
+ * of pointers into itself, and they are only still correct because the
+ * copy is addressed identically.
+ *
+ ****************************************************************************/
+
+int up_addrenv_fork(const arch_addrenv_t *src, arch_addrenv_t *dest)
Review Comment:
the ESP32 has no instruction-bus path to external RAM, so no page-backed
text. Looks like this is specific to esp32s3 (and maybe possibly esp32s2)
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