[Bug 1942895] Re: Build fails on riscv64

[Alexandre Ghiti]

Actually, launchpad builders use qemu-system, not qemu user mode, so the
build used to fail in launchpad because the riscv64 kernel was too old:
v5.8 whereas the commit 38f5bd23deae ("riscv: Add cache information in
AUX vector") that introduced the missing values for pocl landed in
v5.10. So the bump to kernel v5.11 explained the recent build success.

The proposed fix is still valid though for qemu user mode.

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Title:
  Build fails on riscv64

Status in pocl package in Ubuntu:
  In Progress

Bug description:
  Ubuntu release: hirsute/impish

  pocl gets the host machine cache line size using
  getconf(LEVEL1_DCACHE_LINESIZE) and when this value is not defined by
  the underlying architecture, glibc returns 0 which is correctly
  handled by pocl CMakeLists.txt. But riscv64 defines this system
  variable since glibc 2.33 (cf commit 15b38ffc104a ("riscv: Get cache
  information through sysconf")) and amd64 does not. Then when using
  qemu usermode emulation to build pocl for riscv64 on an amd64 host,
  this system variable is not created and then the riscv implementation
  now returns -1 instead of 0, which is mapped to the string "undefined"
  by getconf utility. This value is not handled by pocl and then the
  build fails.

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