Re: [PATCH v4 04/13] LoongArch: ABI Implementation

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 08/05/2022 23:30, caiyinyu wrote:
> ---
> +/* Return the run-time load address of the shared object.  */
> +static inline ElfW (Addr) elf_machine_load_address (void)
> +{
> +  ElfW (Addr) got_linktime_addr;
> +  asm("la.got %0, _GLOBAL_OFFSET_TABLE_"
> +      /* Link-time address in GOT entry before runtime relocation */
> +      : "=r"(got_linktime_addr));
> +  return (ElfW (Addr)) _GLOBAL_OFFSET_TABLE_ - got_linktime_addr;
> +}
> +
> +/* Initial entry point code for the dynamic linker.
> +   The C function `_dl_start' is the real entry point;
> +   its return value is the user program's entry point.  */
> +
> +#define RTLD_START \
> +  asm(".text\n\
> +      " _RTLD_PROLOGUE (ENTRY_POINT) "\
> +      .cfi_label .Ldummy   \n\
> +      " CFI_UNDEFINED (1) "   \n\
> +      or	$a0, $sp, $zero   \n\
> +      bl	_dl_start   \n\
> +      # Stash user entry point in s0.   \n\
> +      or	$s0, $v0, $zero   \n\
> +      # See if we were run as a command with the executable file   \n\
> +      # name as an extra leading argument.   \n\
> +      la	$a0, _dl_skip_args   \n\
> +      ld.w	$a0, $a0, 0   \n\
> +      # Load the original argument count.   \n\
> +      ld.d	$a1, $sp, 0   \n\
> +      # Subtract _dl_skip_args from it.   \n\
> +      sub.d	$a1, $a1, $a0   \n\
> +      # Adjust the stack pointer to skip _dl_skip_args words.   \n\
> +      slli.d	$a0, $a0, 3   \n\
> +      add.d	$sp, $sp, $a0   \n\
> +      # Save back the modified argument count.   \n\
> +      st.d	$a1, $sp, 0   \n\
> +      # Call _dl_init (struct link_map *main_map, int argc, char **argv, \
> +		       char **env)    \n\

Since ad43cac44a6860eaefcadadfb2acb349921e96bf there is no need to adjust the
arguments using _dl_skip_args; if you don't do anything ABI special you just
need to just reload argc from _dl_argc. I have adapted all of architectures to
eventually remove _dl_skip_args [1], so please follow the same pattern here.

[1] https://patchwork.sourceware.org/project/glibc/list/?series=9706

> +      la	$a0, _rtld_local   \n\
> +      ld.d	$a0, $a0, 0   \n\
> +      addi.d	$a2, $sp, 8   \n\
> +      slli.d	$a3, $a1, 3   \n\
> +      add.d	$a3, $a3, $a2   \n\
> +      addi.d	$a3, $a3, 8   \n\
> +      # Adjust $sp for 16-aligned   \n\
> +      srli.d  $t0, $sp, 4   \n\
> +      slli.d  $t0, $t0, 4   \n\
> +      ori	$t1, $sp, 0   \n\
> +      addi.d  $sp, $t0, -32   \n\
> +      st.d	$t1, $sp, 24   \n\
> +      # Call the function to run the initializers.   \n\
> +      bl	_dl_init   \n\
> +      # Pass our finalizer function to _start.   \n\
> +      ld.d    $sp, $sp, 24   \n\
> +      la	$a0, _dl_fini   \n\
> +      # Jump to the user entry point.   \n\
> +      jirl	$zero, $s0, 0   \n\
> +      " _RTLD_EPILOGUE (ENTRY_POINT) "\
> +      .previous");
>