On 5 April 2017 at 18:21, Robin Murphy <robin.murphy@xxxxxxx> wrote: > On 05/04/17 18:08, Ard Biesheuvel wrote: >> Hoi Matthias! >> >> On 5 April 2017 at 17:56, Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote: >>> From: Greg Hackmann <ghackmann@xxxxxxxxxx> >>> >>> The current definition of ASM_EXPORT doesn't work properly with clang, >>> according to https://bugs.llvm.org//show_bug.cgi?id=27250#c3 it relies on >>> gcc specific behavior. Change the constraint from an intermediate to an >>> output expression which works with both gcc and clang. >>> >>> From: Greg Hackmann <ghackmann@xxxxxxxxxx> >>> Commit-message-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> >>> Signed-off-by: Greg Hackmann <ghackmann@xxxxxxxxxx> >>> Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> >>> --- >>> arch/arm64/crypto/sha1-ce-glue.c | 2 +- >>> arch/arm64/crypto/sha2-ce-glue.c | 2 +- >>> 2 files changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c >>> index aefda9868627..c71e94ba0e43 100644 >>> --- a/arch/arm64/crypto/sha1-ce-glue.c >>> +++ b/arch/arm64/crypto/sha1-ce-glue.c >>> @@ -18,7 +18,7 @@ >>> #include <linux/module.h> >>> >>> #define ASM_EXPORT(sym, val) \ >>> - asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val)); >>> + asm(".globl " #sym "; .set " #sym ", %c0" :: "I"(val)); >>> >>> MODULE_DESCRIPTION("SHA1 secure hash using ARMv8 Crypto Extensions"); >>> MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>"); >>> diff --git a/arch/arm64/crypto/sha2-ce-glue.c b/arch/arm64/crypto/sha2-ce-glue.c >>> index 7cd587564a41..381b5fb2dcb2 100644 >>> --- a/arch/arm64/crypto/sha2-ce-glue.c >>> +++ b/arch/arm64/crypto/sha2-ce-glue.c >>> @@ -18,7 +18,7 @@ >>> #include <linux/module.h> >>> >>> #define ASM_EXPORT(sym, val) \ >>> - asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val)); >>> + asm(".globl " #sym "; .set " #sym ", %c0" :: "I"(val)); >>> >>> MODULE_DESCRIPTION("SHA-224/SHA-256 secure hash using ARMv8 Crypto Extensions"); >>> MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>"); >> >> I am fine with this change, although I would really like to add a >> better reference to the commit log. It is *very* difficult to find any >> documentation regarding non-trivial uses of inline asm constraints, >> and if %c0 is the correct syntax, surely we can quote something better >> than a LLVM bugzilla entry? Also, where does the distinction between >> 'intermediate' vs 'output' expression come from? > > FWIW, GCC docs do say (under the helpfully-obvious "x86 operand > modifiers" section[1]): > > c Require a constant operand and print the constant > expression with no punctuation. > > Which more or less makes sense in this this context too. As an aside, > though, since this is emitting a general integer argument to an > assembler directive, and not an operand to an ADD instruction, how come > we're using "I" and not "i" as the constraint in the first place? > No reason. "I" came to mind when writing the code, and worked as expected. Perhaps we should just fix that at the same time.
