[PATCH] Add -fld-path= to specify an arbitrary executable as the linker

Fri Jul 3 13:06:39 GMT 2020

On 7/2/20 9:34 PM, Fāng-ruì Sòng wrote:
> On 2020-07-01, Fāng-ruì Sòng wrote:
>> On 2020-07-01, Martin Liška wrote:
>>> On 6/30/20 5:32 PM, Fāng-ruì Sòng wrote:
>>>> There is some concern about clang's -fuse-ld=path
>>>> http://lists.llvm.org/pipermail/cfe-dev/2020-June/065710.html and use
>>>> of COMPILER_PATH vs PATH.
>>>> Shall we introduce another option like -fld-path=path (PATH is used,
>>>> COMPILER_PATH is not used)?
>>>
>>> I would recommend first landing a patch to LLVM and then we can do
>>> a corresponding change to GCC.
>>>
>>> Martin
>>
>> Thank a lot for you welcoming words! This is what I intend to add for clang: https://reviews.llvm.org/D83015
>>
>> I'll create a GCC patch superseding this one later.
> 
> Attached the new patch.

Thank you for the update patch:

> From e7f86cdcaf03e4ddb98d0df9d07894d9ffb7d91a Mon Sep 17 00:00:00 2001
> From: Fangrui Song <maskray@google.com>
> Date: Thu, 2 Jul 2020 12:26:09 -0700
> Subject: [PATCH] Add -fld-path= to specify an arbitrary executable as the
>  linker
> 
> The value can be either a relative path (relative to a COMPILER_PATH
> directory or a PATH directory) or an absolute path. -fld-path=
> complements -fuse-ld={bfd,gold,lld} which specifies the linker flavor.
> 
> 	PR driver/93645
> 	* common.opt (-fld-path=): Add -fld-path=
> 	* opts.c (common_handle_option): Handle OPT_fld_path_.
> 	* gcc.c (driver_handle_option): Likewise.
> 	* collect2.c (main): Likewise.
> 	* doc/invoke.texi: Document -fld-path=.
> ---
>  gcc/collect2.c      | 57 ++++++++++++++++++++++++++++++++-------------
>  gcc/common.opt      |  4 ++++
>  gcc/doc/invoke.texi |  6 +++++
>  gcc/gcc.c           |  2 +-
>  gcc/opts.c          |  1 +
>  5 files changed, 53 insertions(+), 17 deletions(-)
> 
> diff --git a/gcc/collect2.c b/gcc/collect2.c
> index f8a5ce45994..efa652f7f82 100644
> --- a/gcc/collect2.c
> +++ b/gcc/collect2.c
> @@ -844,6 +844,7 @@ main (int argc, char **argv)
>    const char **ld1;
>    bool use_plugin = false;
>    bool use_collect_ld = false;
> +  const char *ld_path = NULL;
>  
>    /* The kinds of symbols we will have to consider when scanning the
>       outcome of a first pass link.  This is ALL to start with, then might
> @@ -961,12 +962,21 @@ main (int argc, char **argv)
>  	    if (selected_linker == USE_DEFAULT_LD)
>  	      selected_linker = USE_PLUGIN_LD;
>  	  }
> -	else if (strcmp (argv[i], "-fuse-ld=bfd") == 0)
> -	  selected_linker = USE_BFD_LD;
> -	else if (strcmp (argv[i], "-fuse-ld=gold") == 0)
> -	  selected_linker = USE_GOLD_LD;
> -	else if (strcmp (argv[i], "-fuse-ld=lld") == 0)
> -	  selected_linker = USE_LLD_LD;
> +	else if (strncmp (argv[i], "-fuse-ld=bfd", 9) == 0
> +		 && selected_linker != USE_LD_MAX)
> +	  {

This does not seem correct to me. You match -fuse-ld=bfd and then
test other option values in the following block.

> +	    if (strcmp (argv[i] + 9, "bfd") == 0)
> +	      selected_linker = USE_BFD_LD;
> +	    else if (strcmp (argv[i] + 9, "gold") == 0)
> +	      selected_linker = USE_GOLD_LD;
> +	    else if (strcmp (argv[i] + 9, "lld") == 0)
> +	      selected_linker = USE_LLD_LD;
> +	  }
> +	else if (strncmp (argv[i], "-fld-path=", 10) == 0)
> +	  {
> +	    ld_path = argv[i] + 10;
> +	    selected_linker = USE_LD_MAX;
> +	  }
>  	else if (strncmp (argv[i], "-o", 2) == 0)
>  	  {
>  	    /* Parse the output filename if it's given so that we can make
> @@ -1117,14 +1127,27 @@ main (int argc, char **argv)
>        ld_file_name = find_a_file (&cpath, collect_ld_suffix, X_OK);
>        use_collect_ld = ld_file_name != 0;
>      }
> -  /* Search the compiler directories for `ld'.  We have protection against
> -     recursive calls in find_a_file.  */
> -  if (ld_file_name == 0)
> -    ld_file_name = find_a_file (&cpath, ld_suffixes[selected_linker], X_OK);
> -  /* Search the ordinary system bin directories
> -     for `ld' (if native linking) or `TARGET-ld' (if cross).  */
> -  if (ld_file_name == 0)
> -    ld_file_name = find_a_file (&path, full_ld_suffixes[selected_linker], X_OK);
> +  if (selected_linker == USE_LD_MAX)
> +    {
> +      /* If -fld-path= does not contain a slash, search for the command using
> +	 the PATH environment variable.  */

We also support file systems like Windows where the comment about a slash will be misleading.
You can just mention relative vs. absolute path.

> +      if (lbasename (ld_path) == ld_path)

Does it really return the same pointer? Maybe strcmp can be needed?

> +	ld_file_name = find_a_file (&path, ld_path, X_OK);
> +      else if (file_exists (ld_path))
> +	ld_file_name = ld_path;
> +    }
> +  else
> +    {
> +      /* Search the compiler directories for `ld'.  We have protection against
> +	 recursive calls in find_a_file.  */
> +      if (ld_file_name == 0)
> +	ld_file_name = find_a_file (&cpath, ld_suffixes[selected_linker], X_OK);
> +      /* Search the ordinary system bin directories
> +	 for `ld' (if native linking) or `TARGET-ld' (if cross).  */
> +      if (ld_file_name == 0)
> +	ld_file_name =
> +	  find_a_file (&path, full_ld_suffixes[selected_linker], X_OK);
> +    }
>  
>  #ifdef REAL_NM_FILE_NAME
>    nm_file_name = find_a_file (&path, REAL_NM_FILE_NAME, X_OK);
> @@ -1297,9 +1320,11 @@ main (int argc, char **argv)
>  #endif
>  		}
>  	      else if (!use_collect_ld
> -		       && strncmp (arg, "-fuse-ld=", 9) == 0)
> +		       && (strncmp (arg, "-fuse-ld=", 9) == 0 ||
> +			   strncmp (arg, "-fld-path=", 10) == 0))
>  		{
> -		  /* Do not pass -fuse-ld={bfd|gold|lld} to the linker. */
> +		  /* Do not pass -fuse-ld={bfd|gold|lld} or -fld-path= to the
> +		     linker. */
>  		  ld1--;
>  		  ld2--;
>  		}
> diff --git a/gcc/common.opt b/gcc/common.opt
> index df8af365d1b..d5dfbb5c9c6 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -2919,6 +2919,10 @@ fuse-ld=lld
>  Common Driver Negative(fuse-ld=lld)
>  Use the lld LLVM linker instead of the default linker.
>  
> +fld-path=
> +Common Driver Joined
> +Use the specified executable instead of the default linker.
> +
>  fuse-linker-plugin
>  Common Undocumented Var(flag_use_linker_plugin)
>  
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index e21d8a5217b..bfb6222f96b 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -14651,6 +14651,12 @@ Use the @command{gold} linker instead of the default linker.
>  @opindex fuse-ld=lld
>  Use the LLVM @command{lld} linker instead of the default linker.
>  
> +@item -fld-path=@var{linker}
> +@opindex fld-path=linker
> +Use the specified executable named @var{linker} instead of the default linker.
> +If @var{linker} does not contain any slash character, the linker will be
> +searched for using @env{PATH}.  This option overrides @option{-fuse-ld=}.

The slash comment applies here as well.

Martin

> +
>  @cindex Libraries
>  @item -l@var{library}
>  @itemx -l @var{library}
> diff --git a/gcc/gcc.c b/gcc/gcc.c
> index c0eb3c10cfd..a57a3d0aec4 100644
> --- a/gcc/gcc.c
> +++ b/gcc/gcc.c
> @@ -1077,7 +1077,7 @@ proper position among the other output files.  */
>      LINK_PLUGIN_SPEC \
>     "%{flto|flto=*:%<fcompare-debug*} \
>      %{flto} %{fno-lto} %{flto=*} %l " LINK_PIE_SPEC \
> -   "%{fuse-ld=*:-fuse-ld=%*} " LINK_COMPRESS_DEBUG_SPEC \
> +   "%{fuse-ld=*:-fuse-ld=%*} %{fld-path=*:-fld-path=%*} " LINK_COMPRESS_DEBUG_SPEC \
>     "%X %{o*} %{e*} %{N} %{n} %{r}\
>      %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!r:%{!nostartfiles:%S}}} \
>      %{static|no-pie|static-pie:} %@{L*} %(mfwrap) %(link_libgcc) " \
> diff --git a/gcc/opts.c b/gcc/opts.c
> index 340d99434b3..c4507d53abc 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -2750,6 +2750,7 @@ common_handle_option (struct gcc_options *opts,
>      case OPT_fuse_ld_bfd:
>      case OPT_fuse_ld_gold:
>      case OPT_fuse_ld_lld:
> +    case OPT_fld_path_:
>      case OPT_fuse_linker_plugin:
>        /* No-op. Used by the driver and passed to us because it starts with f.*/
>        break;
> -- 
> 2.27.0.383.g050319c2ae-goog
> 