LoongArch: Fix .got.plt dislocation in static PDE
Corrected .got.plt addressing for static executables on LoongArch.
This patch addresses an issue on LoongArch where the .got.plt entry addresses were miscalculated for static Position-Dependent Executables (PDE). The miscalculation stemmed from always accounting for .got.plt entries reserved for ld.so, which are absent in static PDE. This resulted in a two-slot dislocation for all .got.plt entries. The fix unifies code paths to use a correct subroutine, addressing latent issues in ifunc handling as well.
- proposer
Applied the patch, thanking the author.
“Applied, thanks!”
- contributor
Submitted a patch series to fix .got.plt dislocation and related issues in static PDE for LoongArch.
“The code path handling R_LARCH_GOT{64*,{,_PC}_LO12} miscalculated the address of the .got.plt entry: it always counted the two .got.plt entries reserved for ld.so, but in static PDE those two entries do not exist (as in static PDE the PLT is solely for ifunc). Thus all .got.plt entries dislocated for two slots. Those affected relocations are practically always used together with the R_LARCH_GOT…”
Technical Tradeoffs
- Simplifies and unifies relocation handling code.
- Corrects a latent bug that became apparent after changes in a previous release.
In Details
This discussion concerns the LoongArch toolchain's handling of Position-Dependent Executables (PDE) in static builds. Specifically, it addresses incorrect address calculations for .got.plt entries when the dynamic linker stubs are not present in static linking scenarios. The patch unifies several relocation handling paths (R_LARCH_GOT*, R_LARCH_GOT_HI20, R_LARCH_SOP_PUSH_GPREL) to use a common, correct subroutine, thereby fixing latent issues related to ifunc resolution and custom linker scripts.
- .got.plt
- The Global Offset Table section used for Procedure Linkage Table (PLT) entries. It stores addresses of dynamically resolved functions and is essential for dynamic linking.
- static PDE
- Static Position-Dependent Executable. A program that is linked statically (no dynamic shared libraries) but has its code and data addresses fixed at link time, allowing for runtime relocation.
- ifunc
- An Indirect Function, a mechanism in ELF that allows lazy resolution of function pointers. The actual function address is resolved at runtime, typically via a resolver function.
- R_LARCH_GOT_HI20
- A LoongArch relocation type that targets the high 20 bits of a Global Offset Table entry.
- relocation
- A process performed by the linker or dynamic loader to resolve symbolic references between different object files or libraries. It involves adjusting addresses based on the final memory layout.