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[RFC PATCH 14/25] qemu/bswap: Introduce load/store for aligned pointer
From: |
Philippe Mathieu-Daudé |
Subject: |
[RFC PATCH 14/25] qemu/bswap: Introduce load/store for aligned pointer |
Date: |
Tue, 18 May 2021 20:36:44 +0200 |
When the pointer alignment is known to be safe, we can
directly swap the data in place, without having to rely
on the compiler builtin code.
Load/store methods expecting aligned pointer use the 'a'
infix. For example to read a 16-bit unsigned value stored
in little endianess at an unaligned pointer:
val = lduw_le_p(&unaligned_ptr);
then to store it in big endianess at an aligned pointer:
stw_be_ap(&aligned_ptr, val);
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
docs/devel/loads-stores.rst | 27 ++++++++++++++++-----------
include/qemu/bswap.h | 22 ++++++++++++++++++++++
2 files changed, 38 insertions(+), 11 deletions(-)
diff --git a/docs/devel/loads-stores.rst b/docs/devel/loads-stores.rst
index 568274baec0..88493ba1293 100644
--- a/docs/devel/loads-stores.rst
+++ b/docs/devel/loads-stores.rst
@@ -13,20 +13,21 @@ documentation of each API -- for that you should look at the
documentation comments in the relevant header files.
-``ld*_p and st*_p``
-~~~~~~~~~~~~~~~~~~~
+``ld*_[a]p and st*_[a]p``
+~~~~~~~~~~~~~~~~~~~~~~~~~
These functions operate on a host pointer, and should be used
when you already have a pointer into host memory (corresponding
to guest ram or a local buffer). They deal with doing accesses
with the desired endianness and with correctly handling
-potentially unaligned pointer values.
+potentially unaligned pointer values. If the pointer alignment
+is known to be safe, then the aligned functions can be used.
Function names follow the pattern:
-load: ``ld{sign}{size}_{endian}_p(ptr)``
+load: ``ld{sign}{size}_{endian}_{aligned}p(ptr)``
-store: ``st{size}_{endian}_p(ptr, val)``
+store: ``st{size}_{endian}_{aligned}p(ptr, val)``
``sign``
- (empty) : for 32 or 64 bit sizes
@@ -49,24 +50,28 @@ The ``_{endian}`` infix is omitted for target-endian
accesses.
The target endian accessors are only available to source
files which are built per-target.
+By using the ``_{aligned}`` infix, unsafe optimizations might be used,
+however unaligned pointer might trigger an exception and abort the
+process.
+
There are also functions which take the size as an argument:
-load: ``ldn{endian}_p(ptr, sz)``
+load: ``ldn{endian}_{aligned}p(ptr, sz)``
which performs an unsigned load of ``sz`` bytes from ``ptr``
as an ``{endian}`` order value and returns it in a uint64_t.
-store: ``stn{endian}_p(ptr, sz, val)``
+store: ``stn{endian}_{aligned}p(ptr, sz, val)``
which stores ``val`` to ``ptr`` as an ``{endian}`` order value
of size ``sz`` bytes.
Regexes for git grep
- - ``\<ld[us]\?[bwlq]\(_[hbl]e\)\?_p\>``
- - ``\<st[bwlq]\(_[hbl]e\)\?_p\>``
- - ``\<ldn_\([hbl]e\)?_p\>``
- - ``\<stn_\([hbl]e\)?_p\>``
+ - ``\<ld[us]\?[bwlq]\(_[hbl]e\)\?_a?p\>``
+ - ``\<st[bwlq]\(_[hbl]e\)\?_a?p\>``
+ - ``\<ldn_\([hbl]e\)?_a?p\>``
+ - ``\<stn_\([hbl]e\)?_a?p\>``
``cpu_{ld,st}*_mmuidx_ra``
~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/include/qemu/bswap.h b/include/qemu/bswap.h
index 4cd120ca014..3f272c3cb46 100644
--- a/include/qemu/bswap.h
+++ b/include/qemu/bswap.h
@@ -350,25 +350,47 @@ static inline void st ## size ## _he_p(void *ptr, vtype
v)\
__builtin_memcpy(ptr, &v, sizeof(v));\
}
+#define LD_CONVERT_ALIGNED(bits, rtype, vtype, size)\
+static inline rtype ld ## size ## _he_ap(const void *ptr)\
+{\
+ return *(vtype *)ptr;\
+}
+
+#define ST_CONVERT_ALIGNED(bits, vtype, size)\
+static inline void st ## size ## _he_ap(void *ptr, vtype v)\
+{\
+ *(vtype *)ptr = v;\
+}
+
#define LD_CONVERT_END(endian, bits, rtype, vtype, size)\
static inline rtype ld ## size ## _ ## endian ## _p(const void *ptr)\
{\
return (vtype)glue(endian, _bswap)(ld ## size ## _he_p(ptr), bits);\
+}\
+static inline rtype ld ## size ## _ ## endian ## _ap(const void *ptr)\
+{\
+ return (vtype)glue(endian, _bswap)(ld ## size ## _he_ap(ptr), bits);\
}
#define ST_CONVERT_END(endian, bits, vtype, size)\
static inline void st ## size ## _ ## endian ## _p(void *ptr, vtype v)\
{\
st ## size ## _he_p(ptr, glue(endian, _bswap)(v, bits));\
+}\
+static inline void st ## size ## _ ## endian ## _ap(void *ptr, vtype v)\
+{\
+ st ## size ## _he_ap(ptr, glue(endian, _bswap)(v, bits));\
}
#define LD_CONVERT(bits, rtype, vtype, size)\
LD_CONVERT_UNALIGNED(bits, rtype, vtype, size)\
+ LD_CONVERT_ALIGNED(bits, rtype, vtype, size)\
LD_CONVERT_END(le, bits, rtype, vtype, size)\
LD_CONVERT_END(be, bits, rtype, vtype, size)
#define ST_CONVERT(bits, vtype, size)\
ST_CONVERT_UNALIGNED(bits, vtype, size)\
+ ST_CONVERT_ALIGNED(bits, vtype, size)\
ST_CONVERT_END(le, bits, vtype, size)\
ST_CONVERT_END(be, bits, vtype, size)
--
2.26.3
- [RFC PATCH 06/25] exec/memory: Use correct type size, (continued)
- [RFC PATCH 06/25] exec/memory: Use correct type size, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 08/25] qemu/bswap: Use ST_CONVERT() macro to emit 16-bit load/store functions, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 07/25] qemu/bswap: Introduce ST_CONVERT() macro, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 09/25] qemu/bswap: Introduce LD_CONVERT() macro, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 10/25] qemu/bswap: Use LD_CONVERT macro to emit 16-bit signed load/store code, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 11/25] qemu/bswap: Use LD_CONVERT macro to emit 16-bit unsigned load/store code, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 12/25] qemu/bswap: Use LDST_CONVERT macro to emit 32-bit load/store functions, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 13/25] qemu/bswap: Use LDST_CONVERT macro to emit 64-bit load/store functions, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 14/25] qemu/bswap: Introduce load/store for aligned pointer,
Philippe Mathieu-Daudé <=
- [RFC PATCH 16/25] exec/memory: Add methods for aligned pointer access (physical memory), Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 15/25] exec/memory: Add methods for aligned pointer access (address space), Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 17/25] hw/virtio: Use correct type sizes, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 18/25] hw/virtio: Introduce VIRTIO_LD_CONVERT() macro, Philippe Mathieu-Daudé, 2021/05/18
- [RFC PATCH 19/25] hw/virtio: Use LD_CONVERT macro to emit 16-bit unsigned load/store code, Philippe Mathieu-Daudé, 2021/05/18