This reverts and replaces commit 2765b22049 ("probe-app: assume probe
packet aligned"). That commit applied a __builtin_assume_aligned(4) to
every pointer assignment of the following type:
uint32_t *ptr = struct probe_data_packet *packet;
Instead of using __builtin_assume_aligned(4) every time a
probe_data_packet is used like this, the probe_data_packet type
definition is now 32 bits aligned in only one place thanks to (packed,
aligned(4)).
struct probe_data_packet is made entirely of uint32_t members. It
is (packed) to avoid a 64 bits compiler hypothetically padding and
aligning these 32 bits members to 64 bits. However, (packed) alone is
roughly equivalent to aligned(1) (neither is part of the C standard)
which causes some gcc versions to warn about this:
sof/tools/probes/probes_main.c:228:5: error: converting a packed
‘struct probe_data_packet’ pointer (alignment 1) to a ‘uint32_t’
{aka ‘unsigned int’} pointer (alignment 4) may result in an
unaligned pointer value [-Werror=address-of-packed-member]
228 | w_ptr = (uint32_t *)packet;
| ^~~~~
Unlike "assuming" with __builtin_assume_aligned, (packed, aligned(4))
makes sure probe_data_packet are _actually_ 4 bytes aligned. As a
demontration, it stops the following _Static_assert() from failing:
modified src/probe/probe.c
@ -64,9 +64,12 @ struct probe_pdata {
struct probe_dma_ext ext_dma;
struct probe_dma_ext inject_dma[CONFIG_PROBE_DMA_MAX];
struct probe_point probe_points[CONFIG_PROBE_POINTS_MAX];
+ uint8_t dummy;
struct probe_data_packet header; // aligned(4)?
struct task dmap_work;
};
+_Static_assert(offsetof(struct probe_pdata, header) % 4 == 0 ,
+ "probe_data_packet is not 4 aligned");
In addition to gcc version 8 and 9, I tested and confirmed with
_Static_assert and pahole that the same attributes behave the same with
clang 9.0.1-2.fc31.
Signed-off-by: Marc Herbert <marc.herbert@intel.com>
0b80998bb1