The $(CPP) (do only preprocessing) macro is already defined in Makefile.
However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
in flags duplication. Which is not a big deal by itself except for
the flags which depend on other flags and the compiler checks them
as it parses the command line.
Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
If clang+llvm+sanitizer are enabled, this results in
-emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
-fsanitize=cfi-mfcall -fno-lto ...
in the clang command line and triggers error:
clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
This removes unnecessary CPP redefinition. Which works fine as in most
place KBUILD_CFLAGS is passed to $CPP except
arch/powerpc/kernel/vdso64/vdso(32|64).lds. To fix vdso, this does:
1. add -m(big|little)-endian to $CPP
2. add target to $KBUILD_CPPFLAGS as otherwise clang ignores -m(big|little)-endian if
the building platform does not support big endian (such as x86).
Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v3:
* moved vdso cleanup in a separate patch
* only add target to KBUILD_CPPFLAGS for CLANG
v2:
* fix KBUILD_CPPFLAGS
* add CLANG_FLAGS to CPPFLAGS
---
Makefile | 1 +
arch/powerpc/Makefile | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
The $(CPP) (do only preprocessing) macro is already defined in Makefile.
However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
in flags duplication. Which is not a big deal by itself except for
the flags which depend on other flags and the compiler checks them
as it parses the command line.
Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
If clang+llvm+sanitizer are enabled, this results in
-emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
-fsanitize=cfi-mfcall -fno-lto ...
in the clang command line and triggers error:
clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
This removes unnecessary CPP redefinition. Which works fine as in most
place KBUILD_CFLAGS is passed to $CPP except
arch/powerpc/kernel/vdso64/vdso(32|64).lds. To fix vdso, this does:
1. add -m(big|little)-endian to $CPP
2. add target to $KBUILD_CPPFLAGS as otherwise clang ignores -m(big|little)-endian if
the building platform does not support big endian (such as x86).
Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v3:
* moved vdso cleanup in a separate patch
* only add target to KBUILD_CPPFLAGS for CLANG
v2:
* fix KBUILD_CPPFLAGS
* add CLANG_FLAGS to CPPFLAGS
---
Makefile | 1 +
arch/powerpc/Makefile | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
You can avoid the duplication here by just doing:
KBUILD_CPPFLAGS += $(CLANG_FLAGS)
I am still not super happy about the flag duplication but I am not sure
I can think of a better solution. If KBUILD_CPPFLAGS are always included
when building .o files, maybe we should just add $(CLANG_FLAGS) to
KBUILD_CPPFLAGS instead of KBUILD_CFLAGS?
The $(CPP) (do only preprocessing) macro is already defined in Makefile.
However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
in flags duplication. Which is not a big deal by itself except for
the flags which depend on other flags and the compiler checks them
as it parses the command line.
Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
If clang+llvm+sanitizer are enabled, this results in
-emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
-fsanitize=cfi-mfcall -fno-lto ...
in the clang command line and triggers error:
clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed
with '-flto'
This removes unnecessary CPP redefinition. Which works fine as in most
place KBUILD_CFLAGS is passed to $CPP except
arch/powerpc/kernel/vdso64/vdso(32|64).lds. To fix vdso, this does:
1. add -m(big|little)-endian to $CPP
2. add target to $KBUILD_CPPFLAGS as otherwise clang ignores
-m(big|little)-endian if
the building platform does not support big endian (such as x86).
Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v3:
* moved vdso cleanup in a separate patch
* only add target to KBUILD_CPPFLAGS for CLANG
v2:
* fix KBUILD_CPPFLAGS
* add CLANG_FLAGS to CPPFLAGS
---
Makefile | 1 +
arch/powerpc/Makefile | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
You can avoid the duplication here by just doing:
KBUILD_CPPFLAGS += $(CLANG_FLAGS)
This has potential of duplicating even more flags which is exactly what
I am trying to avoid here.
I am still not super happy about the flag duplication but I am not sure
I can think of a better solution. If KBUILD_CPPFLAGS are always included
when building .o files,
My understanding is that KBUILD_CPPFLAGS should not be added for .o. Who
does know or decide for sure about what CPPFLAGS are for? :)
maybe we should just add $(CLANG_FLAGS) to
KBUILD_CPPFLAGS instead of KBUILD_CFLAGS?
On Fri, May 14, 2021 at 3:59 AM Nathan Chancellor [off-list ref] wrote:
On 5/13/2021 4:59 AM, Alexey Kardashevskiy wrote:
quoted
The $(CPP) (do only preprocessing) macro is already defined in Makefile.
However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
in flags duplication. Which is not a big deal by itself except for
the flags which depend on other flags and the compiler checks them
as it parses the command line.
Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
If clang+llvm+sanitizer are enabled, this results in
-emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
-fsanitize=cfi-mfcall -fno-lto ...
in the clang command line and triggers error:
I do not know how to reproduce this for powerpc.
Currently, only x86 and arm64 select
ARCH_SUPPORTS_LTO_CLANG.
Is this a fix for a potential issue?
quoted
clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
This removes unnecessary CPP redefinition. Which works fine as in most
place KBUILD_CFLAGS is passed to $CPP except
arch/powerpc/kernel/vdso64/vdso(32|64).lds. To fix vdso, this does:
1. add -m(big|little)-endian to $CPP
2. add target to $KBUILD_CPPFLAGS as otherwise clang ignores -m(big|little)-endian if
the building platform does not support big endian (such as x86).
Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v3:
* moved vdso cleanup in a separate patch
* only add target to KBUILD_CPPFLAGS for CLANG
v2:
* fix KBUILD_CPPFLAGS
* add CLANG_FLAGS to CPPFLAGS
---
Makefile | 1 +
arch/powerpc/Makefile | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
You can avoid the duplication here by just doing:
KBUILD_CPPFLAGS += $(CLANG_FLAGS)
I am still not super happy about the flag duplication but I am not sure
I can think of a better solution. If KBUILD_CPPFLAGS are always included
when building .o files, maybe we should just add $(CLANG_FLAGS) to
KBUILD_CPPFLAGS instead of KBUILD_CFLAGS?
Hmm, I think including --target=* in CPP flags is sensible,
but not all CLANG_FLAGS are CPP flags.
At least, -(no)-integrated-as is not a CPP flag.
We could introduce a separate CLANG_CPP_FLAGS, but
it would require more code changes...
So, I do not have a strong opinion either way.
BTW, another approach might be to modify the linker script.
In my best guess, the reason why powerpc adding the endian flag to CPP
is this line in arch/powerpc/kernel/vdso64/vdso64.lds.S
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#endif
You can use the CONFIG option to check the endian-ness.
#ifdef CONFIG_CPU_BIG_ENDIAN
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#else
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#endif
All the big endian arches define CONFIG_CPU_BIG_ENDIAN.
(but not all little endian arches define CONFIG_CPU_LITTLE_ENDIAN)
So,
#ifdef CONFIG_CPU_BIG_ENDIAN
< big endian code >
#else
< little endian code >
#endif
works for all architectures.
Only the exception is you cannot replace the one in uapi headers.
arch/powerpc/include/uapi/asm/byteorder.h: #ifdef __LITTLE_ENDIAN__
since it is exported to userspace, where CONFIG options are not available.
BTW, various flags are historically used.
- CONFIG_CPU_BIG_ENDIAN / CONFIG_CPU_LITTLE_ENDIAN
- __BIG_ENDIAN / __LITTLE_ENDIAN
- __LITTLE_ENDIAN__ (powerpc only)
__LITTLE_ENDIAN__ is defined by powerpc gcc and clang.
My experiments...
[1] powerpc-linux-gnu-gcc -> __BIG_ENDIAN__ is defined
masahiro@grover:~$ echo | powerpc-linux-gnu-gcc -E -dM -x c - | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __BIG_ENDIAN__ 1
#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define _BIG_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __VEC_ELEMENT_REG_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
[2] powerpc-linux-gnu-gcc + -mlittle-endian -> __LITTLE_ENDIAN__ is defined
masahiro@grover:~$ echo | powerpc-linux-gnu-gcc -E -dM -x c -
-mlittle-endian | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define _LITTLE_ENDIAN 1
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __LITTLE_ENDIAN__ 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __VEC_ELEMENT_REG_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
[3] other arch gcc -> neither of them is defined
masahiro@grover:~$ echo | gcc -E -dM -x c - | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __ORDER_BIG_ENDIAN__ 4321
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
masahiro@grover:~$ echo | arm-linux-gnueabihf-gcc -E -dM -x c -
-mlittle-endian | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
masahiro@grover:~$ echo | arm-linux-gnueabihf-gcc -E -dM -x c -
-mbig-endian | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __ARM_BIG_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
[4] Clang --target=powerpc-linux-gnu -> __BIG_ENDIAN__ is defined
masahiro@grover:~$ echo | ~/tools/clang-latest/bin/clang -E
--target=powerpc-linux-gnu -dM -x c - | grep ENDIAN
#define _BIG_ENDIAN 1
#define __BIG_ENDIAN__ 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
[5] very recent Clang understands --target=powerpcle-linux-gnu -->
__LITTLE_ENDIAN__ is defined
masahiro@grover:~$ echo | ~/tools/clang-latest/bin/clang -E
--target=powerpcle-linux-gnu -dM -x c - | grep ENDIAN
#define _LITTLE_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
[6] very recent Clang, --target=powerpc-linux-gnu + -mlittle-endian
--> __LITTLE_ENDIAN__ is defined
masahiro@grover:~$ echo | ~/tools/clang-latest/bin/clang -E
--target=powerpc-linux-gnu -dM -x c - -mlittle-endian | grep ENDIAN
#define _LITTLE_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
[7] Clang, target with little endian only , -mbig-endian is ignored
masahiro@grover:~$ echo | clang -E -dM -x c - | grep ENDIAN
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
masahiro@grover:~$ echo | clang -E -dM -x c - -mbig-endian | grep ENDIAN
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
--
Best Regards
Masahiro Yamada
On Fri, May 14, 2021 at 3:59 AM Nathan Chancellor [off-list ref] wrote:
quoted
On 5/13/2021 4:59 AM, Alexey Kardashevskiy wrote:
quoted
The $(CPP) (do only preprocessing) macro is already defined in Makefile.
However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
in flags duplication. Which is not a big deal by itself except for
the flags which depend on other flags and the compiler checks them
as it parses the command line.
Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
If clang+llvm+sanitizer are enabled, this results in
-emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
-fsanitize=cfi-mfcall -fno-lto ...
in the clang command line and triggers error:
I do not know how to reproduce this for powerpc.
Currently, only x86 and arm64 select
ARCH_SUPPORTS_LTO_CLANG.
Is this a fix for a potential issue?
clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
This removes unnecessary CPP redefinition. Which works fine as in most
place KBUILD_CFLAGS is passed to $CPP except
arch/powerpc/kernel/vdso64/vdso(32|64).lds. To fix vdso, this does:
1. add -m(big|little)-endian to $CPP
2. add target to $KBUILD_CPPFLAGS as otherwise clang ignores -m(big|little)-endian if
the building platform does not support big endian (such as x86).
Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v3:
* moved vdso cleanup in a separate patch
* only add target to KBUILD_CPPFLAGS for CLANG
v2:
* fix KBUILD_CPPFLAGS
* add CLANG_FLAGS to CPPFLAGS
---
Makefile | 1 +
arch/powerpc/Makefile | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
You can avoid the duplication here by just doing:
KBUILD_CPPFLAGS += $(CLANG_FLAGS)
I am still not super happy about the flag duplication but I am not sure
I can think of a better solution. If KBUILD_CPPFLAGS are always included
when building .o files, maybe we should just add $(CLANG_FLAGS) to
KBUILD_CPPFLAGS instead of KBUILD_CFLAGS?
Hmm, I think including --target=* in CPP flags is sensible,
but not all CLANG_FLAGS are CPP flags.
At least, -(no)-integrated-as is not a CPP flag.
We could introduce a separate CLANG_CPP_FLAGS, but
it would require more code changes...
So, I do not have a strong opinion either way.
BTW, another approach might be to modify the linker script.
In my best guess, the reason why powerpc adding the endian flag to CPP
is this line in arch/powerpc/kernel/vdso64/vdso64.lds.S
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#endif
You can use the CONFIG option to check the endian-ness.
#ifdef CONFIG_CPU_BIG_ENDIAN
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#else
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#endif
All the big endian arches define CONFIG_CPU_BIG_ENDIAN.
(but not all little endian arches define CONFIG_CPU_LITTLE_ENDIAN)
This should work with .lds. But missing --target=* might still hit us
somewhere else later, these include 3 header files each and there might
be endianness dependent stuff.
So,
#ifdef CONFIG_CPU_BIG_ENDIAN
< big endian code >
#else
< little endian code >
#endif
works for all architectures.
Only the exception is you cannot replace the one in uapi headers.
arch/powerpc/include/uapi/asm/byteorder.h: #ifdef __LITTLE_ENDIAN__
since it is exported to userspace, where CONFIG options are not available.
BTW, various flags are historically used.
- CONFIG_CPU_BIG_ENDIAN / CONFIG_CPU_LITTLE_ENDIAN
- __BIG_ENDIAN / __LITTLE_ENDIAN
- __LITTLE_ENDIAN__ (powerpc only)
__LITTLE_ENDIAN__ is defined by powerpc gcc and clang.
My experiments...
[1] powerpc-linux-gnu-gcc -> __BIG_ENDIAN__ is defined
masahiro@grover:~$ echo | powerpc-linux-gnu-gcc -E -dM -x c - | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __BIG_ENDIAN__ 1
#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define _BIG_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __VEC_ELEMENT_REG_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
[2] powerpc-linux-gnu-gcc + -mlittle-endian -> __LITTLE_ENDIAN__ is defined
masahiro@grover:~$ echo | powerpc-linux-gnu-gcc -E -dM -x c -
-mlittle-endian | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define _LITTLE_ENDIAN 1
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __LITTLE_ENDIAN__ 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __VEC_ELEMENT_REG_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
[3] other arch gcc -> neither of them is defined
masahiro@grover:~$ echo | gcc -E -dM -x c - | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __ORDER_BIG_ENDIAN__ 4321
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
masahiro@grover:~$ echo | arm-linux-gnueabihf-gcc -E -dM -x c -
-mlittle-endian | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
masahiro@grover:~$ echo | arm-linux-gnueabihf-gcc -E -dM -x c -
-mbig-endian | grep ENDIAN
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __ARM_BIG_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
[4] Clang --target=powerpc-linux-gnu -> __BIG_ENDIAN__ is defined
masahiro@grover:~$ echo | ~/tools/clang-latest/bin/clang -E
--target=powerpc-linux-gnu -dM -x c - | grep ENDIAN
#define _BIG_ENDIAN 1
#define __BIG_ENDIAN__ 1
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
[5] very recent Clang understands --target=powerpcle-linux-gnu -->
__LITTLE_ENDIAN__ is defined
masahiro@grover:~$ echo | ~/tools/clang-latest/bin/clang -E
--target=powerpcle-linux-gnu -dM -x c - | grep ENDIAN
#define _LITTLE_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
[6] very recent Clang, --target=powerpc-linux-gnu + -mlittle-endian
--> __LITTLE_ENDIAN__ is defined
masahiro@grover:~$ echo | ~/tools/clang-latest/bin/clang -E
--target=powerpc-linux-gnu -dM -x c - -mlittle-endian | grep ENDIAN
#define _LITTLE_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
[7] Clang, target with little endian only , -mbig-endian is ignored
masahiro@grover:~$ echo | clang -E -dM -x c - | grep ENDIAN
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
masahiro@grover:~$ echo | clang -E -dM -x c - -mbig-endian | grep ENDIAN
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
Hi!
On Fri, May 14, 2021 at 11:42:32AM +0900, Masahiro Yamada wrote:
In my best guess, the reason why powerpc adding the endian flag to CPP
is this line in arch/powerpc/kernel/vdso64/vdso64.lds.S
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#endif
Which is equivalent to
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc")
#endif
so please change that at the same time if you touch this :-)
__LITTLE_ENDIAN__ is defined by powerpc gcc and clang.
This predefined macro is required by the newer ABIs, but all older
compilers have it as well. _LITTLE_ENDIAN is not supported on all
platforms (but it is if your compiler targets Linux, which you cannot
necessarily rely on). These macros are PowerPC-specific.
For GCC, for all targets, you can say
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
You do not need any of the other *ORDER__ macros in most cases.
See "info cpp" for the sordid details.
[2] powerpc-linux-gnu-gcc + -mlittle-endian -> __LITTLE_ENDIAN__ is defined
You can just write -mbig and -mlittle btw. Those aren't available on
all targets, but neither are the long-winded -m{big,little}-endian
option names. Pet peeve, I know :-)
HtH,
Segher
Hi!
On Fri, May 14, 2021 at 11:42:32AM +0900, Masahiro Yamada wrote:
quoted
In my best guess, the reason why powerpc adding the endian flag to CPP
is this line in arch/powerpc/kernel/vdso64/vdso64.lds.S
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#endif
Which is equivalent to
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc")
#endif
so please change that at the same time if you touch this :-)
"If you touch this" approach did not work well with this patch so sorry
but no ;)
and for a separate patch, I'll have to dig since when it is equal, do
you know?
quoted
__LITTLE_ENDIAN__ is defined by powerpc gcc and clang.
This predefined macro is required by the newer ABIs, but all older
That's good so I'll stick to it.
compilers have it as well. _LITTLE_ENDIAN is not supported on all
platforms (but it is if your compiler targets Linux, which you cannot
necessarily rely on). These macros are PowerPC-specific.
For GCC, for all targets, you can say
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
You do not need any of the other *ORDER__ macros in most cases.
See "info cpp" for the sordid details.
quoted
[2] powerpc-linux-gnu-gcc + -mlittle-endian -> __LITTLE_ENDIAN__ is defined
You can just write -mbig and -mlittle btw. Those aren't available on
all targets, but neither are the long-winded -m{big,little}-endian
option names. Pet peeve, I know :-)
I am looking the same guarantees across modern enough gcc and clang and
I am not sure all of the above is valid for clang 10.0.something (or
whatever we say we support) ;)
--
Alexey
Hi!
On Mon, May 17, 2021 at 01:23:11PM +1000, Alexey Kardashevskiy wrote:
On 5/14/21 18:46, Segher Boessenkool wrote:
quoted
On Fri, May 14, 2021 at 11:42:32AM +0900, Masahiro Yamada wrote:
quoted
In my best guess, the reason why powerpc adding the endian flag to CPP
is this line in arch/powerpc/kernel/vdso64/vdso64.lds.S
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#endif
Which is equivalent to
#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc")
#endif
so please change that at the same time if you touch this :-)
"If you touch this" approach did not work well with this patch so sorry
but no ;)
and for a separate patch, I'll have to dig since when it is equal, do
you know?
Since 1994, when the three-arg version was introduced (the one-arg
version is from 1992).
quoted
quoted
__LITTLE_ENDIAN__ is defined by powerpc gcc and clang.
This predefined macro is required by the newer ABIs, but all older
That's good so I'll stick to it.
Great.
quoted
You can just write -mbig and -mlittle btw. Those aren't available on
all targets, but neither are the long-winded -m{big,little}-endian
option names. Pet peeve, I know :-)
I am looking the same guarantees across modern enough gcc and clang and
I am not sure all of the above is valid for clang 10.0.something (or
whatever we say we support) ;)
-mbig/-mlittle is supported in GCC since times immemorial. Whether LLVM
supports it as well just depends on how good their emulation is, I have
no idea.
Segher