[Bug binutils/28986] New: RISC-V Binutils Lacks Support for ELF symbol table reloc info

[john.leidel at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28986

            Bug ID: 28986
           Summary: RISC-V Binutils Lacks Support for ELF symbol table
                    reloc info
           Product: binutils
           Version: 2.37
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: john.leidel at gmail dot com
  Target Milestone: ---

Created attachment 14030
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14030&action=edit
driver.c, patchlib.c, makefile and run script for the bug

Tested platforms: 
RISC-V RV64G Binutils 2.36.1 & 2.37; Ubuntu 21.04 & 21.10, respectively. 
Platform: SiFive HiFive Unmatched

We are porting a parallel runtime library that requires us to provide support
for "patching" existing system functions such as mmap/munmap/etc with
user-defined functions.  The process of which requires that we dlopen a new
library, walks its symbol table, gather info on each symbol, then reloc the new
functions into the existing runtime environment.  This process requires that we
use the r_info indices into the PTR in order to lookup all the provided
functionality from a shared library.  It appears that this information is not
currently implemented for the RISC-V target.  RISC-V contains the necessary
macros in libdl that provide the DT_JMPREL and DT_PLTRELSZ references. 
However, attempted to access the contents of each DT_PLTRELSZ index causes a
segmentation as these appear to not be implemented currently.

The attached bug and associated makefile provide two source files.  The
"driver.c" is the actual code that attempts to dlopen and patch an existing
function.  The patchlib.c provides a sample function (patch_calloc) that should
patch the existing `calloc` function call.  The attached tgz includes both
files, a makefile and a run script.  The lack of the r_info struct being
implemented induces a segmentation fault in the program as follows:

$> gdb ./a.out
(gdb) r ./libpatchlib.so patch_calloc

0x0000002aaaaaacbe in visit_symbols (inf=0x0, dlpi_addr=183251935232,
table=0x8a0, table_size=456,
    strtab=0x568, symtab=0x2c8, dl_name=0x3fffffc878 "(anonymous dl @
0x2aaaaaa000)") at driver.c:87
87              elf_sym = (char*)strtab +
symtab[ELF64_R_SYM(reloc->r_info)].st_name;

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