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
* build-globals.sh
- Macros for defining symbols etc. based on assembler in use
- Use the System.map to get all the nuttx symbols
* libs/libc/modlib/modlib_globals.S
- Provide an empty skeleton. If the dynamic loading functions
are required then run build-global.sh after a clean build
using the skeleton. This will fill out the skeleton with the
symbols to be available to dynamically loaded modules.
* libs/libc/modlib/modlib_loadhdrs.c
- Fix case where there are no program headers are avaiable
* libs/libc/machine/arm/armv7-m/arch_elf.c
- Fix cast of error message parameters
* build-globals.sh
- Build the modlib_globals.S file used to resolve symbols when dynamically loading
* libs/libc/modlib/Make.defs
- Build modlib_globals.S for all targets
* libs/libc/modlib/modlib_load.c
- Calculate sizes and text/data addresses based on program headers rather than section headers
- Handle objects with no program headers
* libs/libc/modlib/modlib_bind.c
- Call modlib_readsym with pointer to symbol table
- Add modlib_relocatedyn to manage relocation of symbols with shared object (ET_DYN)
- Differentiate between ET_REL and ET_DYN objects
- Use arch independent symbol ELF_R_SYM
- Cast sizes to avoid warnings
* libs/libc/modlib/modlib_load.c
- Cast sizes to avoid warnings
* include/elf.h
- Add definitions that may be found in shared objects
* include/nuttx/lib/modlib.h
- Add parameter to modlib_readsym prototype
- Add prototypes for:
- modlib_insertsymtab
- modlib_findglobal
- Define Elf_Dyn and Elf_Off according to the elf architecture
- Add fields to mod_loadifno_s:
- Program headers
- Exported symbols
- Data section address
- Padding requirement
- Section index for dynamic symbol table
- Number of symbols exported
- Add prottotype for modlib_freesymtab
* libs/libc/dlfcn/lib_dlclose.c
- Free the symbol table when the dll is closed
* libs/libc/dlfcn/lib_dlopen.c
- Add dump of program headers to debug routine
- Differentiate between ET_REL and ET_DYN objects
* libs/libc/machine/arm/armv7-m/arch_elf.c
- Add handling of R_ARM_RELATIVE and R_ARM_JUMP slot relocation types
* libs/libc/modlib/modlib_loadshdrs.c
- Rename modlib_loadshdrs.c to modlib_loadhdrs.c
- Rename modlib_loadshdrs to modlib_loadhdrs
- Add code to load program headers
* libs/libc/modlib/modlib_symbols.c
- Define entry point structure
- Add offset parameter to modlib_symname() and use to find symbol names
- Add symtab section header parameter to modlib_readsym()
- Add offset parameter to modlib_symvalue() to locate symbol names
- Add modlib_insertsyntab() to create a symbol table for exporting and resolution
- Add findEP() to resolve a symbol in the modlib_global table
- Add modlib_findglobal() to find symbol in the modlib_global table
- Add modlib_freesymtab() to free the symbol table
* libs/libc/modlib/modlib_uninit.c
- Free header and sections from a module_loadinfo_s control block
* libs/libc/modlib/modlib_verify.c
- Handle ET_DYN shared objects
* libs/libc/modlib/modlib_globals.S
- Multi-target global table
- Define library APIs that may be resolved when loading a shared object
since symbols defined in arch/elf.h is also used in other case, for example:
CC: pthread/pthread_testcancel.c machine/arm/gnu_unwind_find_exidx.c:32:8: error: unknown type name '__EIT_entry'
32 | static __EIT_entry *__exidx_start_elf;
| ^~~~~~~~~~~
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
The following errors are intentionally left.
They are a part of tables which are not trivial to fix.
libs/libc/machine/arm/armv7-m/arch_elf.c:230:94: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:232:89: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:240:94: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:242:89: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:403:94: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:405:91: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:413:94: error: Long line found
libs/libc/machine/arm/armv7-m/arch_elf.c:415:91: error: Long line found
Squashed commit of the following:
libs/libxx: Fix some confusing in naming. If the directory is called libxx, then the library must be libxx.a (unless perhaps LIBCXX is selected).
libs/: Fix paths in moved library directories.
libs: Brute force move of libc, libnx, and libxx to libs. Cannot yet build it in that configuration.
