linux-kernel - [PATCH 01/10] Documentation: raise minimum supported version of GCC to 5.1

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Date:   Fri, 10 Sep 2021 16:40:38 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 01/10] Documentation: raise minimum supported version of GCC
 to 5.1

commit fad7cd3310db ("nbd: add the check to prevent overflow in
__nbd_ioctl()")

raised an issue from the fallback helpers added in

commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code")

Specifically, the helpers for checking whether the results of a
multiplication overflowed (__unsigned_mul_overflow,
__signed_add_overflow) use the division operator when
!COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b
operands on 32b hosts.

Also, because the macro is type agnostic, it is very difficult to write
a similarly type generic macro that dispatches to one of:
* div64_s64
* div64_u64
* div_s64
* div_u64

Raising the minimum supported versions allows us to remove all of the
fallback helpers for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW, instead
dispatching the compiler builtins.

arm64 has already raised the minimum supported GCC version to 5.1, do
this for all targets now. See the link below for the previous
discussion.

Link: https://lore.kernel.org/all/20210909182525.372ee687@canb.auug.org.au/
Link: https://lore.kernel.org/lkml/CAK7LNASs6dvU6D3jL2GG3jW58fXfaj6VNOe55NJnTB8UPuk2pA@mail.gmail.com/
Link: https://github.com/ClangBuiltLinux/linux/issues/1438
Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
Reported-by: Nathan Chancellor <nathan@...nel.org>
Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Documentation/process/changes.rst | 2 +-
 scripts/min-tool-version.sh       | 8 +-------
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
index d3a8557b66a1..e35ab74a0f80 100644
--- a/Documentation/process/changes.rst
+++ b/Documentation/process/changes.rst
@@ -29,7 +29,7 @@ you probably needn't concern yourself with pcmciautils.
 ====================== ===============  ========================================
         Program        Minimal version       Command to check the version
 ====================== ===============  ========================================
-GNU C                  4.9              gcc --version
+GNU C                  5.1              gcc --version
 Clang/LLVM (optional)  10.0.1           clang --version
 GNU make               3.81             make --version
 binutils               2.23             ld -v
diff --git a/scripts/min-tool-version.sh b/scripts/min-tool-version.sh
index 319f92104f56..4edc708baa63 100755
--- a/scripts/min-tool-version.sh
+++ b/scripts/min-tool-version.sh
@@ -17,13 +17,7 @@ binutils)
 	echo 2.23.0
 	;;
 gcc)
-	# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
-	# https://lore.kernel.org/r/20210107111841.GN1551@shell.armlinux.org.uk
-	if [ "$SRCARCH" = arm64 ]; then
-		echo 5.1.0
-	else
-		echo 4.9.0
-	fi
+	echo 5.1.0
 	;;
 icc)
 	# temporary
-- 
2.33.0.309.g3052b89438-goog