hw/core/loader: Add new function rom_ptr_for_as()

For accesses to rom blob data before or during reset, we have a
function rom_ptr() which looks for a rom blob that would be loaded to
the specified address, and returns a pointer into the rom blob data
corresponding to that address.  This allows board or CPU code to say
"what is the data that is going to be loaded to this address?".

However, this function does not take account of memory region
aliases.  If for instance a machine model has RAM at address
0x0000_0000 which is aliased to also appear at 0x1000_0000, a
rom_ptr() query for address 0x0000_0000 will only return a match if
the guest image provided by the user was loaded at 0x0000_0000 and
not if it was loaded at 0x1000_0000, even though they are the same
RAM and a run-time guest CPU read of 0x0000_0000 will read the data
loaded to 0x1000_0000.

Provide a new function rom_ptr_for_as() which takes an AddressSpace
argument, so that it can check whether the MemoryRegion corresponding
to the address is also mapped anywhere else in the AddressSpace and
look for rom blobs that loaded to that alias.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210318174823.18066-5-peter.maydell@linaro.org

1 files changed, 31 insertions, 0 deletions

diff --git a/include/hw/loader.h b/include/hw/loader.h
index a9eeea3..cbfc184 100644
--- a/include/hw/loader.h
+++ b/include/hw/loader.h
@@ -290,6 +290,37 @@ void rom_transaction_end(bool commit);
 
 int rom_copy(uint8_t *dest, hwaddr addr, size_t size);
 void *rom_ptr(hwaddr addr, size_t size);
+/**
+ * rom_ptr_for_as: Return a pointer to ROM blob data for the address
+ * @as: AddressSpace to look for the ROM blob in
+ * @addr: Address within @as
+ * @size: size of data required in bytes
+ *
+ * Returns: pointer into the data which backs the matching ROM blob,
+ * or NULL if no blob covers the address range.
+ *
+ * This function looks for a ROM blob which covers the specified range
+ * of bytes of length @size starting at @addr within the address space
+ * @as. This is useful for code which runs as part of board
+ * initialization or CPU reset which wants to read data that is part
+ * of a user-supplied guest image or other guest memory contents, but
+ * which runs before the ROM loader's reset function has copied the
+ * blobs into guest memory.
+ *
+ * rom_ptr_for_as() will look not just for blobs loaded directly to
+ * the specified address, but also for blobs which were loaded to an
+ * alias of the region at a different location in the AddressSpace.
+ * In other words, if a machine model has RAM at address 0x0000_0000
+ * which is aliased to also appear at 0x1000_0000, rom_ptr_for_as()
+ * will return the correct data whether the guest image was linked and
+ * loaded at 0x0000_0000 or 0x1000_0000.  Contrast rom_ptr(), which
+ * will only return data if the image load address is an exact match
+ * with the queried address.
+ *
+ * New code should prefer to use rom_ptr_for_as() instead of
+ * rom_ptr().
+ */
+void *rom_ptr_for_as(AddressSpace *as, hwaddr addr, size_t size);
 void hmp_info_roms(Monitor *mon, const QDict *qdict);
 
 #define rom_add_file_fixed(_f, _a, _i)          \