Re: [Patch][GCC] Document and fix -r (partial linking)

[Allan Sandfeld Jensen <linux at carewolf dot com>]

On Mittwoch, 1. August 2018 18:32:30 CEST Joseph Myers wrote:
> On Wed, 1 Aug 2018, Allan Sandfeld Jensen wrote:
> > gcc/
> > 
> >     * gcc.c: Correct default specs for -r
> 
> I don't follow why your changes (which would need describing for each
> individual spec changed) are corrections.
> 
> >  /* config.h can define LIB_SPEC to override the default libraries.  */
> >  #ifndef LIB_SPEC
> > 
> > -#define LIB_SPEC "%{!shared:%{g*:-lg}
> > %{!p:%{!pg:-lc}}%{p:-lc_p}%{pg:-lc_p}}" +#define LIB_SPEC
> > "%{!shared|!r:%{g*:-lg} %{!p:%{!pg:-lc}}%{p:-lc_p}%{pg:-lc_p}}"> 
> >  #endif
> 
> '!' binds more closely than '|' in specs.  That is, !shared|!r means the
> following specs are used unless both -shared and -r are specified, which
> seems nonsensical to me.  I'd expect something more like "shared|r:;" to
> expand to nothing if either -shared or -r is passed and to what follows if
> neither is passed.
> 
> And that ignores that this LIB_SPEC value in gcc.c is largely irrelevant,
> as it's generally overridden by targets - and normally for targets using
> ELF shared libraries, for example, -lc *does* have to be used when linking
> with -shared.
> 
> I think you're changing the wrong place for this.  If you want -r to be
> usable with GCC without using -nostdlib (which is an interesting
> question), you actually need to change LINK_COMMAND_SPEC (also sometimes
> overridden for targets) to handle -r more like -nostdlib -nostartfiles.
> 
Okay, so like this?

>From 9de68f2ef0b77a0c0bcf0d83232e7fc34b006406 Mon Sep 17 00:00:00 2001
From: Allan Sandfeld Jensen <allan.jensen@qt.io>
Date: Wed, 1 Aug 2018 18:07:05 +0200
Subject: [PATCH] Fix and document -r option

The option has existed and been working for years,
make sure it implies the right extra options, and list
it in the documentation.

2018-07-29 Allan Sandfeld Jensen <allan.jensen@qt.io>

gcc/doc

    * invoke.texi: Document -r

gcc/
    * gcc.c (LINK_COMMAND_SPEC): Handle -r like -nostdlib
    * config/darwin.h (LINK_COMMAND_SPEC): Handle -r like -nostdlib
---
 gcc/config/darwin.h | 8 ++++----
 gcc/doc/invoke.texi | 7 ++++++-
 gcc/gcc.c           | 6 +++---
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
index 980ad9b4057..6ad657a4958 100644
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -178,20 +178,20 @@ extern GTY(()) int darwin_ms_struct;
    "%X %{s} %{t} %{Z} %{u*} \
     %{e*} %{r} \
     %{o*}%{!o:-o a.out} \
-    %{!nostdlib:%{!nostartfiles:%S}} \
+    %{!nostdlib:%{!r:%{!nostartfiles:%S}}} \
     %{L*} %(link_libgcc) %o %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} \
     %{fopenacc|fopenmp|%:gt(%{ftree-parallelize-loops=*:%*} 1): \
       %{static|static-libgcc|static-libstdc++|static-libgfortran: libgomp.a%s; : -lgomp } } \
     %{fgnu-tm: \
       %{static|static-libgcc|static-libstdc++|static-libgfortran: libitm.a%s; : -litm } } \
-    %{!nostdlib:%{!nodefaultlibs:\
+    %{!nostdlib:%{!r:%{!nodefaultlibs:\
       %{%:sanitize(address): -lasan } \
       %{%:sanitize(undefined): -lubsan } \
       %(link_ssp) \
       " DARWIN_EXPORT_DYNAMIC " %<rdynamic \
       %(link_gcc_c_sequence) \
-    }}\
-    %{!nostdlib:%{!nostartfiles:%E}} %{T*} %{F*} }}}}}}}"
+    }}}\
+    %{!nostdlib:%{!r:%{!nostartfiles:%E}}} %{T*} %{F*} }}}}}}}"
 
 #define DSYMUTIL "\ndsymutil"
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 6047d82065a..7da30bd9d99 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -518,7 +518,7 @@ Objective-C and Objective-C++ Dialects}.
 @xref{Link Options,,Options for Linking}.
 @gccoptlist{@var{object-file-name}  -fuse-ld=@var{linker}  -l@var{library} @gol
 -nostartfiles  -nodefaultlibs  -nolibc  -nostdlib @gol
--pie  -pthread  -rdynamic @gol
+-pie  -pthread  -r  -rdynamic @gol
 -s  -static -static-pie -static-libgcc  -static-libstdc++ @gol
 -static-libasan  -static-libtsan  -static-liblsan  -static-libubsan @gol
 -shared  -shared-libgcc  -symbolic @gol
@@ -12444,6 +12444,11 @@ x86 Cygwin and MinGW targets.  On some targets this option also sets
 flags for the preprocessor, so it should be used consistently for both
 compilation and linking.
 
+@item -r
+@opindex r
+Produce a relocatable object as output. This is also known as partial
+linking.
+
 @item -rdynamic
 @opindex rdynamic
 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
diff --git a/gcc/gcc.c b/gcc/gcc.c
index 780d4859ef3..687903cb1be 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -1041,7 +1041,7 @@ proper position among the other output files.  */
     %{flto} %{fno-lto} %{flto=*} %l " LINK_PIE_SPEC \
    "%{fuse-ld=*:-fuse-ld=%*} " LINK_COMPRESS_DEBUG_SPEC \
    "%X %{o*} %{e*} %{N} %{n} %{r}\
-    %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!nostartfiles:%S}} \
+    %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!r:%{!nostartfiles:%S}}} \
     %{static|no-pie|static-pie:} %@{L*} %(mfwrap) %(link_libgcc) " \
     VTABLE_VERIFICATION_SPEC " " SANITIZER_EARLY_SPEC " %o "" \
     %{fopenacc|fopenmp|%:gt(%{ftree-parallelize-loops=*:%*} 1):\
@@ -1049,8 +1049,8 @@ proper position among the other output files.  */
     %{fgnu-tm:%:include(libitm.spec)%(link_itm)}\
     %(mflib) " STACK_SPLIT_SPEC "\
     %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} " SANITIZER_SPEC " \
-    %{!nostdlib:%{!nodefaultlibs:%(link_ssp) %(link_gcc_c_sequence)}}\
-    %{!nostdlib:%{!nostartfiles:%E}} %{T*}  \n%(post_link) }}}}}}"
+    %{!nostdlib:%{!r:%{!nodefaultlibs:%(link_ssp) %(link_gcc_c_sequence)}}}\
+    %{!nostdlib:%{!r:%{!nostartfiles:%E}}} %{T*}  \n%(post_link) }}}}}}"
 #endif
 
 #ifndef LINK_LIBGCC_SPEC
-- 
2.17.0