[gcc r10-7322] Darwin: Fix i686 bootstrap when the assembler supports GOTOFF in data.

[gcc r10-7322] Darwin: Fix i686 bootstrap when the assembler supports GOTOFF in data.

[Iain D Sandoe]

https://gcc.gnu.org/g:85e10e4f0fa5c6b1a9f3caf7d9cab28ef8490a83

commit r10-7322-g85e10e4f0fa5c6b1a9f3caf7d9cab28ef8490a83
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sun Mar 22 09:27:05 2020 +0000

    Darwin: Fix i686 bootstrap when the assembler supports GOTOFF in data.
    
    When we use an assembler that supports " .long XX@GOTOFF", the current
    combination of configuration parameters and conditional compilation
    (when building an i686-darwin compiler with mdynamic-no-pic) assume that
    it's OK to put jump tables in the .const section.
    
    However, when we encounter a weak function with a jump table, this
    produces relocations that directly access the weak symbol section from
    the .const section - which is deemed illegal by the linker (since that
    would mean that the weak symbol could not be replaced).
    
    Arguably, this is a limitation (maybe even a bug) in the linker - but
    it seems that we'd have to change the ABI to fix it - since it would
    require some annotation (maybe just using a special section for the
    jump tables) to tell the linker that this specific circumstance is OK
    because the direct access to the weak symbol can only occur from that
    symbol itself.
    
    The fix is to force jump tables into the text section for all X86 Darwin
    versions (PIC code already had this change).
    
    gcc/ChangeLog:
    
    2020-03-22  Iain Sandoe  <iain@sandoe.co.uk>
    
            * config/i386/darwin.h (JUMP_TABLES_IN_TEXT_SECTION): Remove
            references to Darwin.
            * config/i386/i386.h (JUMP_TABLES_IN_TEXT_SECTION): Define this
            unconditionally and comment on why.

Diff:
---
 gcc/ChangeLog            |  7 +++++++
 gcc/config/i386/darwin.h | 10 ++++++++++
 gcc/config/i386/i386.h   |  5 ++---
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b691ac991bd..96883830929 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2020-03-22  Iain Sandoe  <iain@sandoe.co.uk>
+
+	* config/i386/darwin.h (JUMP_TABLES_IN_TEXT_SECTION): Remove
+	references to Darwin.
+	* config/i386/i386.h (JUMP_TABLES_IN_TEXT_SECTION): Define this
+	unconditionally and comment on why.
+
 2020-03-21 Iain Sandoe <iain@sandoe.co.uk>
 
 	* config/darwin.c (darwin_mergeable_constant_section): Collect
diff --git a/gcc/config/i386/darwin.h b/gcc/config/i386/darwin.h
index 1b94cb88c98..5faa1f40089 100644
--- a/gcc/config/i386/darwin.h
+++ b/gcc/config/i386/darwin.h
@@ -239,6 +239,16 @@ along with GCC; see the file COPYING3.  If not see
 #undef TARGET_ASM_OUTPUT_IDENT
 #define TARGET_ASM_OUTPUT_IDENT default_asm_output_ident_directive
 
+/* We always want jump tables in the text section:
+   * for PIC code, we need the subtracted symbol to be defined at
+     assembly-time.
+   * for mdynamic-no-pic, we cannot support jump tables in the .const
+     section for weak functions, this looks to ld64 like direct access
+     to the weak symbol from an anonymous atom.  */
+
+#undef JUMP_TABLES_IN_TEXT_SECTION
+#define JUMP_TABLES_IN_TEXT_SECTION 1
+
 /* Darwin profiling -- call mcount.
    If we need a stub, then we unconditionally mark it as used.  */
 #undef FUNCTION_PROFILER
diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index 98235f75a9e..b8dddfc1594 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -2285,11 +2285,10 @@ extern int const svr4_dbx_register_map[FIRST_PSEUDO_REGISTER];
 
 /* Under some conditions we need jump tables in the text section,
    because the assembler cannot handle label differences between
-   sections.  This is the case for x86_64 on Mach-O for example.  */
+   sections.  */
 
 #define JUMP_TABLES_IN_TEXT_SECTION \
-  (flag_pic && ((TARGET_MACHO && TARGET_64BIT) \
-   || (!TARGET_64BIT && !HAVE_AS_GOTOFF_IN_DATA)))
+  (flag_pic && !(TARGET_64BIT || HAVE_AS_GOTOFF_IN_DATA))
 
 /* Switch to init or fini section via SECTION_OP, emit a call to FUNC,
    and switch back.  For x86 we do this only to save a few bytes that