Re: [PATCH v2 3/3] trace: fix undefined behavior in register

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 30 Jan 2025 15:58:49 +0100
David Marchand <david.marchand@redhat.com> wrote:

> Registering a tracepoint handler was resulting so far in undefined
> behavior at runtime.
> 
> The RTE_TRACE_POINT_REGISTER() macro was casting the tracepoint handler
> (which expects arguments) to a void (*)(void).
> At runtime, calling this handler while registering resulted in
> reading the current stack with no relation to this function prototype.
> 
> Instead, declare an additional inline _register() handler for each
> tracepoint and make sure that the emitting macros in
> rte_trace_point_register.h only work on arguments name and type.
> 
> The original tracepoint handler prototype is adjusted by adding a
> __rte_unused for each argument (since emitting macros do nothing
> with them).
> This last part introduces an implementation limit of 15 arguments.
> 
> With this change in place, the workaround in dmadev tracepoints can be
> removed.
> 
> Signed-off-by: David Marchand <david.marchand@redhat.com>

When I build with -Db_santize=undefined the following warning shows up.
It seems related.

In function ‘rte_ethdev_trace_get_dcb_info’,
    inlined from ‘rte_eth_dev_get_dcb_info’ at ../lib/ethdev/rte_ethdev.c:6720:2:
../lib/eal/include/rte_trace_point.h:381:9: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  381 |         memcpy(mem, &(in), sizeof(in)); \
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../lib/eal/include/rte_trace_point.h:53:9: note: in definition of macro ‘__RTE_TRACE_POINT’
   53 |         __VA_ARGS__ \
      |         ^~~~~~~~~~~
../lib/ethdev/ethdev_trace.h:1213:1: note: in expansion of macro ‘RTE_TRACE_POINT’
 1213 | RTE_TRACE_POINT(
      | ^~~~~~~~~~~~~~~
../lib/eal/include/rte_trace_point.h:399:9: note: in expansion of macro ‘__rte_trace_point_emit’
  399 |         __rte_trace_point_emit(len, uint8_t); \
      |         ^~~~~~~~~~~~~~~~~~~~~~
../lib/ethdev/ethdev_trace.h:1223:9: note: in expansion of macro ‘rte_trace_point_emit_blob’
 1223 |         rte_trace_point_emit_blob(dcb_info->tc_bws, num_tcs);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘rte_eth_dev_get_dcb_info’:
cc1: note: destination object is likely at address zero
In function ‘rte_ethdev_trace_get_dcb_info’,
    inlined from ‘rte_eth_dev_get_dcb_info’ at ../lib/ethdev/rte_ethdev.c:6720:2:
../lib/eal/include/rte_trace_point.h:401:9: warning: ‘memset’ offset [0, 55] is out of the bounds [0, 0] [-Warray-bounds=]
  401 |         memset(RTE_PTR_ADD(mem, len), 0, RTE_TRACE_BLOB_LEN_MAX - len); \
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../lib/eal/include/rte_trace_point.h:53:9: note: in definition of macro ‘__RTE_TRACE_POINT’
   53 |         __VA_ARGS__ \
      |         ^~~~~~~~~~~
../lib/ethdev/ethdev_trace.h:1213:1: note: in expansion of macro ‘RTE_TRACE_POINT’
 1213 | RTE_TRACE_POINT(
      | ^~~~~~~~~~~~~~~
../lib/ethdev/ethdev_trace.h:1222:9: note: in expansion of macro ‘rte_trace_point_emit_blob’
 1222 |         rte_trace_point_emit_blob(dcb_info->prio_tc, num_user_priorities);