pussuw opened a new pull request, #11322:
URL: https://github.com/apache/nuttx/pull/11322
## Summary
There is a problem with the current elf loader for risc-v: when a pair of
PCREL_HI20 / LO12 relocations are encountered, it is assumed that these will
follow each other immediately, as follows:
label:
auipc a0, %pcrel_hi(symbol) // R_RISCV_PCREL_HI20
load/store a0, %pcrel_lo(label)(a0) // R_RISCV_PCREL_LO12_I/S
With this assumption, the hi/lo relocations are both done when a hi20
relocation entry is encountered, first to the current instruction (addr) and to
the next instruction (addr + 4).
However, this assumption is wrong. There is nothing in the elf relocation
specification[1] that mandates this. Thus, the hi/lo relocation always needs to
first fixup the hi-part, and when the lo-part is encountered, it needs to find
the corresponding hi relocation entry, via the given "label". This necessitates
(re-)visiting the relocation entries for the current section as well as looking
for "label" in the symbol table.
The NuttX elf loader does not allow such operations to be done in the
machine specific part, so this patch fixes the relocation issue by introducing
an architecture specific cache for the hi20 relocation and symbol table
entries. When a lo12 relocation is encountered, the cache can be consulted to
find the hi20 part.
[1]
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc
## Impact
Fix elf loader for risc-v
## Testing
qemu-rv:knsh64
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