RTEMS | bsps/mips/malta: The boot command line pointer holds a loop counter (#5766)

[Sebastian Huber (@sebhub)]

Issue created by Sebastian Huber: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5766



The init code of `bsps/mips/malta/start/start.S` puts the instruction
which clears `a0` into the delay slot of the `jal` to `init_tlb`. The
zero therefore reaches `init_tlb` and not `boot_card`. The comment on
the instruction states the intent, which is a command line of zero
for `boot_card()`.

`init_tlb()` calls `resettlb()` for every entry and leaves the
counter of its loop in `a0`. That counter is `N_TLB_ENTRIES`, which
is 16 for this processor. `boot_card()` takes 16 as the address of
the command line and stores it in `bsp_boot_cmdline`.

`Init()` of `cpukit/libmisc/dummy/default-configuration.c` reads that
pointer and counts the arguments of the string. `defaultconfig01`
takes a TLB load exception in `strlen()` at address 16 and makes no
further progress. `bspcmdline01` reads the same variable and fails as
well. The two are the last failures of the BSP.

The five other MIPS BSPs clear `a0` in ordinary code ahead of the
`jal` and put a `nop` in the delay slot. Only this BSP calls
`init_tlb()` there, and only this BSP loses the value.

Put the instruction which clears `a0` into the delay slot of the
`jal` to `boot_card`.

Found in the repair of the Malta BSP for the test suite. This
description was created with Claude Code assistance.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5766
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