From 31732efcb4de06ae0714989998eb29238cb48a1e Mon Sep 17 00:00:00 2001
From: Ben Gamari <ben@smart-cactus.org>
Date: Sun, 31 Mar 2019 16:00:34 -0400
Subject: [PATCH] configure: Always use AC_LINK_ELSEIF when testing against
assembler
This fixes #16440, where the build system incorrectly concluded that the
`.subsections_via_symbols` assembler directive was supported on a Linux
system. This was caused by the fact that gcc was invoked with `-flto`;
when so-configured gcc does not call the assembler but rather simply
serialises its AST for compilation during the final link.
This is described in Note [autoconf assembler checks and -flto].
(cherry picked from commit 7b090b53fea065d2cfd967ea919426af9ba8d737)
---
aclocal.m4 | 38 +++++++++++++++++++++++++++++++++-----
1 file changed, 33 insertions(+), 5 deletions(-)
diff --git a/aclocal.m4 b/aclocal.m4
index 87b7e8519aed..6eda09431551 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -288,11 +288,31 @@ AC_DEFUN([FPTOOLS_SET_HASKELL_PLATFORM_VARS],
esac
}
+ dnl Note [autoconf assembler checks and -flto]
+ dnl ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ dnl
+ dnl Autoconf's AC_COMPILE_IFELSE macro is fragile in the case of checks
+ dnl which require that the assembler is run. Specifically, GCC does not run
+ dnl the assembler if invoked with `-c -flto`; it merely dumps its internal
+ dnl AST to the object file, to be compiled and assembled during the final
+ dnl link.
+ dnl
+ dnl This can cause configure checks like that for the
+ dnl .subsections_via_symbols directive to pass unexpected (see #16440),
+ dnl leading the build system to incorrectly conclude that the directive is
+ dnl supported.
+ dnl
+ dnl For this reason, it is important that configure checks that rely on the
+ dnl assembler failing use AC_LINK_IFELSE rather than AC_COMPILE_IFELSE,
+ dnl ensuring that the assembler sees the check.
+ dnl
+
dnl ** check for Apple-style dead-stripping support
dnl (.subsections-via-symbols assembler directive)
AC_MSG_CHECKING(for .subsections_via_symbols)
- AC_COMPILE_IFELSE(
+ dnl See Note [autoconf assembler checks and -flto]
+ AC_LINK_IFELSE(
[AC_LANG_PROGRAM([], [__asm__ (".subsections_via_symbols");])],
[AC_MSG_RESULT(yes)
HaskellHaveSubsectionsViaSymbols=True
@@ -305,8 +325,9 @@ AC_DEFUN([FPTOOLS_SET_HASKELL_PLATFORM_VARS],
dnl ** check for .ident assembler directive
AC_MSG_CHECKING(whether your assembler supports .ident directive)
- AC_COMPILE_IFELSE(
- [AC_LANG_SOURCE([__asm__ (".ident \"GHC x.y.z\"");])],
+ dnl See Note [autoconf assembler checks and -flto]
+ AC_LINK_IFELSE(
+ [AC_LANG_PROGRAM([__asm__ (".ident \"GHC x.y.z\"");], [])],
[AC_MSG_RESULT(yes)
HaskellHaveIdentDirective=True],
[AC_MSG_RESULT(no)
@@ -330,8 +351,15 @@ AC_DEFUN([FPTOOLS_SET_HASKELL_PLATFORM_VARS],
;;
esac
AC_MSG_CHECKING(for GNU non-executable stack support)
- AC_COMPILE_IFELSE(
- [AC_LANG_PROGRAM([__asm__ (".section .note.GNU-stack,\"\",$progbits");], [0])],
+ dnl See Note [autoconf assembler checks and -flto]
+ AC_LINK_IFELSE(
+ dnl the `main` function is placed after the .note.GNU-stack directive
+ dnl so we need to ensure that the active segment is correctly set,
+ dnl otherwise `main` will be placed in the wrong segment.
+ [AC_LANG_PROGRAM([
+ __asm__ (".section .note.GNU-stack,\"\",$progbits");
+ __asm__ (".section .text");
+ ], [0])],
[AC_MSG_RESULT(yes)
HaskellHaveGnuNonexecStack=True],
[AC_MSG_RESULT(no)
--
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