[Driver] Add support for -fuse-ld=lld

[Romain GEISSLER]

Ping^2

> Le 27 oct. 2018 à 11:33, Romain GEISSLER <romain.geissler@amadeus.com> a écrit :
> 
> Ping
> 
>> Le 20 oct. 2018 à 12:18, Romain Geissler <romain.geissler@amadeus.com> a écrit :
>> 
>> Hi,
>> 
>> I would like to raise again the question of supporting -fuse-ld=ldd. A
>> patch implementing it was already submitted in
>> https://gcc.gnu.org/ml/gcc-patches/2016-06/msg01722.html by Davide
>> Italiano. This patch still applies correctly to current trunk. I am CC-ing
>> the original author and re-posting it here unchanged for reference.
>> 
>> I think we can consider this patch as relevant despite the goals and
>> licence difference of LLVM vs GNU, based on what was written by Mike Stump
>> in https://gcc.gnu.org/ml/gcc-patches/2016-07/msg00157.html
>> 
>> Back then, the technical problem raised by lld was reported as
>> https://bugs.llvm.org/show_bug.cgi?id=28414 now closed. In this bug, every
>> reported problems have been fixed except the last one. H.J. Lu mentions
>> this last problem (lld does not produces symbol versions predecessor
>> relationship while ld.bfd and ld.gold do, which seems to be a decision
>> taken on purpose and advertised as a harmless change) as being one reason
>> against supporting in -fuse-ld=ldd in gcc. Is it still the case today, and
>> if yes, why ?
>> 
>> Is there any other reason why -fuse-ld=ldd shall not be supported by gcc ?
>> 
>> Cheers,
>> Romain
>> 
>> From 323c23d79c91d7dcee2f29b9ced8c1c00703d346 Mon Sep 17 00:00:00 2001
>> From: Davide Italiano <dccitaliano@gmail.com>
>> Date: Thu, 23 Jun 2016 20:51:53 -0700
>> Subject: [PATCH] Driver: Add support for -fuse-ld=lld.
>> 
>> * collect2.c  (main): Support -fuse-ld=lld.
>> 
>> * common.opt: Add fuse-ld=lld
>> 
>> * doc/invoke.texi:  Document -fuse-ld=lld
>> 
>> * opts.c: Ignore -fuse-ld=lld
>> ---
>> gcc/collect2.c      | 11 ++++++++---
>> gcc/common.opt      |  4 ++++
>> gcc/doc/invoke.texi |  4 ++++
>> gcc/opts.c          |  1 +
>> 4 files changed, 17 insertions(+), 3 deletions(-)
>> 
>> diff --git a/gcc/collect2.c b/gcc/collect2.c
>> index bffac80..6a8387c 100644
>> --- a/gcc/collect2.c
>> +++ b/gcc/collect2.c
>> @@ -831,6 +831,7 @@ main (int argc, char **argv)
>>      USE_PLUGIN_LD,
>>      USE_GOLD_LD,
>>      USE_BFD_LD,
>> +      USE_LLD_LD,
>>      USE_LD_MAX
>>    } selected_linker = USE_DEFAULT_LD;
>>  static const char *const ld_suffixes[USE_LD_MAX] =
>> @@ -838,7 +839,8 @@ main (int argc, char **argv)
>>      "ld",
>>      PLUGIN_LD_SUFFIX,
>>      "ld.gold",
>> -      "ld.bfd"
>> +      "ld.bfd",
>> +      "ld.lld"
>>    };
>>  static const char *const real_ld_suffix = "real-ld";
>>  static const char *const collect_ld_suffix = "collect-ld";
>> @@ -1004,6 +1006,8 @@ main (int argc, char **argv)
>> 	  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;
>> 
>> #ifdef COLLECT_EXPORT_LIST
>> 	/* These flags are position independent, although their order
>> @@ -1093,7 +1097,8 @@ main (int argc, char **argv)
>>  /* Maybe we know the right file to use (if not cross).  */
>>  ld_file_name = 0;
>> #ifdef DEFAULT_LINKER
>> -  if (selected_linker == USE_BFD_LD || selected_linker == USE_GOLD_LD)
>> +  if (selected_linker == USE_BFD_LD || selected_linker == USE_GOLD_LD ||
>> +      selected_linker == USE_LLD_LD)
>>    {
>>      char *linker_name;
>> # ifdef HOST_EXECUTABLE_SUFFIX
>> @@ -1307,7 +1312,7 @@ main (int argc, char **argv)
>> 	      else if (!use_collect_ld
>> 		       && strncmp (arg, "-fuse-ld=", 9) == 0)
>> 		{
>> -		  /* Do not pass -fuse-ld={bfd|gold} to the linker. */
>> +		  /* Do not pass -fuse-ld={bfd|gold|lld} to the linker. */
>> 		  ld1--;
>> 		  ld2--;
>> 		}
>> diff --git a/gcc/common.opt b/gcc/common.opt
>> index 5d90385..2a95a1f 100644
>> --- a/gcc/common.opt
>> +++ b/gcc/common.opt
>> @@ -2536,6 +2536,10 @@ fuse-ld=gold
>> Common Driver Negative(fuse-ld=bfd)
>> Use the gold linker instead of the default linker.
>> 
>> +fuse-ld=lld
>> +Common Driver Negative(fuse-ld=lld)
>> +Use the lld LLVM linker 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 2c87c53..4b8acff 100644
>> --- a/gcc/doc/invoke.texi
>> +++ b/gcc/doc/invoke.texi
>> @@ -10651,6 +10651,10 @@ Use the @command{bfd} linker instead of the default linker.
>> @opindex fuse-ld=gold
>> Use the @command{gold} linker instead of the default linker.
>> 
>> +@item -fuse-ld=lld
>> +@opindex fuse-ld=lld
>> +Use the LLVM @command{lld} linker instead of the default linker.
>> +
>> @cindex Libraries
>> @item -l@var{library}
>> @itemx -l @var{library}
>> diff --git a/gcc/opts.c b/gcc/opts.c
>> index 7406210..f2c86f7 100644
>> --- a/gcc/opts.c
>> +++ b/gcc/opts.c
>> @@ -2178,6 +2178,7 @@ common_handle_option (struct gcc_options *opts,
>> 
>>    case OPT_fuse_ld_bfd:
>>    case OPT_fuse_ld_gold:
>> +    case OPT_fuse_ld_lld:
>>    case OPT_fuse_linker_plugin:
>>      /* No-op. Used by the driver and passed to us because it starts with f.*/
>>      break;
>