AMPI datatypes: CkDDT_Struct ignores member trueLB; negative extents from Type_create_resized can terminate the program

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Issue 类型
缺陷
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基本清楚
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技术栈
cpp
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backend, hpc

调研方向

Start in src/libs/ck-libs/ampi/ddt.C and read the CkDDT_Struct true lower bound calculation and the scan code changed in #4085. Reproduce the nested vector case with a negative displacement, then check MPI_Type_get_true_extent and scan buffer bounds; also try a resized datatype with a negative extent and count of at least two. Done when true lower bounds include member types and the negative-extent case no longer terminates the program.

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描述

Split out of #4072 (from Aditya's re-review of #4085; pre-existing on recharm, not fixed). Both in src/libs/ck-libs/ampi/ddt.C.

  1. CkDDT_Struct takes trueLB from the block displacements only and ignores each member type's own trueLB: struct{(0, 1, vector(2,1,-1,MPI_INT))} reports trueLB 0 but the vector writes at offset -4. MPI_Type_get_true_extent reports the same wrong value, and the scan (which since #4085 sizes its buffers from trueLB) writes just before its buffer for such types.
  2. Negative extents from MPI_Type_create_resized can terminate the program: with count >= 2 the scan's span count * max(extent, trueExtent) can be negative, std::vector throws, and the throw happens inside a noexcept function.

Related: #4085 (scan family).

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