[U-Boot] [RFC PATCH 1/2] Makefile: Use -fno-strict-aliasing globally

[U-Boot] [RFC PATCH 1/2] Makefile: Use -fno-strict-aliasing globally

[Bin Meng]

The -fstrict-aliasing option is implicitly enabled at levels -O2,
-O3, -Os by GCC. This option allows the compiler to assume the
strictest aliasing rules applicable to the language being compiled.
For example, the practice of reading from a different union member
than the one most recently written to (called "type-punning") is
common. In this case, "type-punning" only works if the memory is
accessed through the union type, but might not work by taking the
address, casting the resulting pointer and dereferencing the result,
which is an undefined behavior per the "strict aliasing rules".

GCC's -Wstrict-aliasing (included in -Wall) option does not catch
all cases, but does attempt to catch the more common pitfalls. So
there are cases that GCC does not report but the codes are violating
the "strict aliasing rules".

Given lots of codes that may be written to rely on "type-punning",
and Linux kernel disables it by -fno-strict-aliasing globally, since
U-Boot currently does this on nds32/riscv/x86 builds only, extend
this for all architecture builds.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
---

 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index f30dd8e..994d957 100644
--- a/Makefile
+++ b/Makefile
@@ -372,7 +372,7 @@ KBUILD_CPPFLAGS := -D__KERNEL__ -D__UBOOT__
 KBUILD_CFLAGS   := -Wall -Wstrict-prototypes \
 		   -Wno-format-security \
 		   -fno-builtin -ffreestanding $(CSTD_FLAG)
-KBUILD_CFLAGS	+= -fshort-wchar
+KBUILD_CFLAGS	+= -fshort-wchar -fno-strict-aliasing
 KBUILD_AFLAGS   := -D__ASSEMBLY__
 
 # Don't generate position independent code
-- 
2.7.4

[U-Boot] [RFC PATCH 2/2] config.mk: Remove duplicated -fno-strict-aliasing

[Bin Meng]

Now that we already disable the "strict-aliasing" globally, remove
the duplicates in the nds32/riscv/x86 arch-specific Makefiles.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

---

 arch/nds32/config.mk | 2 +-
 arch/riscv/config.mk | 2 +-
 arch/x86/config.mk   | 1 -
 3 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/nds32/config.mk b/arch/nds32/config.mk
index cb3d8b3..c5520fd 100644
--- a/arch/nds32/config.mk
+++ b/arch/nds32/config.mk
@@ -15,7 +15,7 @@ endif
 CONFIG_STANDALONE_LOAD_ADDR = 0x300000 \
 			      -T $(srctree)/examples/standalone/nds32.lds
 
-PLATFORM_RELFLAGS	+= -fno-strict-aliasing -fno-common -mrelax
+PLATFORM_RELFLAGS	+= -fno-common -mrelax
 PLATFORM_RELFLAGS	+= -gdwarf-2
 PLATFORM_CPPFLAGS	+= -D__nds32__ -G0 -ffixed-10 -fpie
 
diff --git a/arch/riscv/config.mk b/arch/riscv/config.mk
index 219e666..c0b3858 100644
--- a/arch/riscv/config.mk
+++ b/arch/riscv/config.mk
@@ -31,7 +31,7 @@ CONFIG_STANDALONE_LOAD_ADDR = 0x00000000 \
 			      -T $(srctree)/examples/standalone/riscv.lds
 
 PLATFORM_CPPFLAGS	+= -ffixed-gp -fpic
-PLATFORM_RELFLAGS += -fno-strict-aliasing -fno-common -gdwarf-2 -ffunction-sections
+PLATFORM_RELFLAGS += -fno-common -gdwarf-2 -ffunction-sections
 LDFLAGS_u-boot += --gc-sections -static -pie
 
 EFI_CRT0		:= crt0_riscv_efi.o
diff --git a/arch/x86/config.mk b/arch/x86/config.mk
index 5b04feb..cc94071 100644
--- a/arch/x86/config.mk
+++ b/arch/x86/config.mk
@@ -5,7 +5,6 @@
 
 CONFIG_STANDALONE_LOAD_ADDR ?= 0x40000
 
-PLATFORM_CPPFLAGS += -fno-strict-aliasing
 PLATFORM_CPPFLAGS += -fomit-frame-pointer
 PF_CPPFLAGS_X86   := $(call cc-option, -fno-toplevel-reorder, \
 		     $(call cc-option, -fno-unit-at-a-time))
-- 
2.7.4

[U-Boot] [RFC PATCH 1/2] Makefile: Use -fno-strict-aliasing globally

[Tom Rini]

On Mon, Sep 10, 2018 at 06:53:45AM -0700, Bin Meng wrote:

> The -fstrict-aliasing option is implicitly enabled at levels -O2,
> -O3, -Os by GCC. This option allows the compiler to assume the
> strictest aliasing rules applicable to the language being compiled.
> For example, the practice of reading from a different union member
> than the one most recently written to (called "type-punning") is
> common. In this case, "type-punning" only works if the memory is
> accessed through the union type, but might not work by taking the
> address, casting the resulting pointer and dereferencing the result,
> which is an undefined behavior per the "strict aliasing rules".
> 
> GCC's -Wstrict-aliasing (included in -Wall) option does not catch
> all cases, but does attempt to catch the more common pitfalls. So
> there are cases that GCC does not report but the codes are violating
> the "strict aliasing rules".
> 
> Given lots of codes that may be written to rely on "type-punning",
> and Linux kernel disables it by -fno-strict-aliasing globally, since
> U-Boot currently does this on nds32/riscv/x86 builds only, extend
> this for all architecture builds.
> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

Reviewed-by: Tom Rini <trini@konsulko.com>

-- 
Tom
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[U-Boot] [RFC PATCH 2/2] config.mk: Remove duplicated -fno-strict-aliasing

[Rick Chen]

 > From: Bin Meng [mailto:bmeng.cn at gmail.com]
 > Sent: Monday, September 10, 2018 9:54 PM
 > To: Simon Glass; Tom Rini; Rick Jian-Zhi Chen(陳建志); U-Boot Mailing List
 > Cc: Tuomas Tynkkynen
 > Subject: [RFC PATCH 2/2] config.mk: Remove duplicated -fno-strict-aliasing
 >
 > Now that we already disable the "strict-aliasing" globally, remove
the duplicates
 > in the nds32/riscv/x86 arch-specific Makefiles.
 >
 > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
 >
 > ---
 >
 >  arch/nds32/config.mk | 2 +-
 >  arch/riscv/config.mk | 2 +-
 >  arch/x86/config.mk   | 1 -
 >  3 files changed, 2 insertions(+), 3 deletions(-)
 >
 > diff --git a/arch/nds32/config.mk b/arch/nds32/config.mk index
cb3d8b3..c5520fd
 > 100644
 > --- a/arch/nds32/config.mk
 > +++ b/arch/nds32/config.mk
 > @@ -15,7 +15,7 @@ endif
 >  CONFIG_STANDALONE_LOAD_ADDR = 0x300000 \
 >                             -T $(srctree)/examples/standalone/nds32.lds
 >
 > -PLATFORM_RELFLAGS    += -fno-strict-aliasing -fno-common -mrelax
 > +PLATFORM_RELFLAGS    += -fno-common -mrelax
 >  PLATFORM_RELFLAGS    += -gdwarf-2
 >  PLATFORM_CPPFLAGS    += -D__nds32__ -G0 -ffixed-10 -fpie
 >
 > diff --git a/arch/riscv/config.mk b/arch/riscv/config.mk index
219e666..c0b3858
 > 100644
 > --- a/arch/riscv/config.mk
 > +++ b/arch/riscv/config.mk
 > @@ -31,7 +31,7 @@ CONFIG_STANDALONE_LOAD_ADDR = 0x00000000 \
 >                             -T $(srctree)/examples/standalone/riscv.lds
 >
 >  PLATFORM_CPPFLAGS    += -ffixed-gp -fpic
 > -PLATFORM_RELFLAGS += -fno-strict-aliasing -fno-common -gdwarf-2
 > -ffunction-sections
 > +PLATFORM_RELFLAGS += -fno-common -gdwarf-2 -ffunction-sections
 >  LDFLAGS_u-boot += --gc-sections -static -pie
 >

Reviewed-by: Rick Chen <rick@andestech.com>


 >  EFI_CRT0             := crt0_riscv_efi.o
 > diff --git a/arch/x86/config.mk b/arch/x86/config.mk index 5b04feb..cc94071
 > 100644
 > --- a/arch/x86/config.mk
 > +++ b/arch/x86/config.mk
 > @@ -5,7 +5,6 @@
 >
 >  CONFIG_STANDALONE_LOAD_ADDR ?= 0x40000
 >
 > -PLATFORM_CPPFLAGS += -fno-strict-aliasing  PLATFORM_CPPFLAGS +=
 > -fomit-frame-pointer
 >  PF_CPPFLAGS_X86   := $(call cc-option, -fno-toplevel-reorder, \
 >                    $(call cc-option, -fno-unit-at-a-time))

[U-Boot] [RFC PATCH 1/2] Makefile: Use -fno-strict-aliasing globally

[Simon Glass]

On 10 September 2018 at 15:53, Bin Meng <bmeng.cn@gmail.com> wrote:
> The -fstrict-aliasing option is implicitly enabled at levels -O2,
> -O3, -Os by GCC. This option allows the compiler to assume the
> strictest aliasing rules applicable to the language being compiled.
> For example, the practice of reading from a different union member
> than the one most recently written to (called "type-punning") is
> common. In this case, "type-punning" only works if the memory is
> accessed through the union type, but might not work by taking the
> address, casting the resulting pointer and dereferencing the result,
> which is an undefined behavior per the "strict aliasing rules".
>
> GCC's -Wstrict-aliasing (included in -Wall) option does not catch
> all cases, but does attempt to catch the more common pitfalls. So
> there are cases that GCC does not report but the codes are violating
> the "strict aliasing rules".
>
> Given lots of codes that may be written to rely on "type-punning",
> and Linux kernel disables it by -fno-strict-aliasing globally, since
> U-Boot currently does this on nds32/riscv/x86 builds only, extend
> this for all architecture builds.
>
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> ---
>
>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Simon Glass <sjg@chromium.org>